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Polyurethane

2009-04-14 18:39:25  
The M/T Haven (formerly Amoco Milford Haven), was a VLCC (Very Large Crude Carrier), leased to Troodos Shipping (a company ran by Lucas Haji-Ioannou and his son Stelios Haji-Ioannou). In 1991, while loaded with 144,000 tonnes (1 million barrels) of crude oil, the ship exploded, caught fire and sank off the coast of Genoa, Italy, killing six Cypriot crew and flooding the Merranean with up to 50,000 tonnes of crude oil.1 It broke in two and sank after burning for three days, and for the next 12 years the Merranean coast of Italy and France was polluted, especially around Genoa and southern France.

 

 

History

The Amoco Milford Haven was built by Astilleros Espanoles S.A in Cadiz, Spain, the twin sister ship to the Amoco Cadiz, which itself sank in 1978. Launched in 1973, she worked various routes shipping crude oil from the middle east gulf. In 1987 she was hit by a missile in the Persian Gulf during the Iran-Iraq War. Extensively refitted in Singapore, she was sold to ship brokers who leased her to Troodos Shipping, for whom she ran from Iran's Kharg Island to the Merranean.

 

Accident

On 11 April 1991, the Haven was unloading a cargo of 230,000 tonnes of crude oil to the Multedo floating platform, seven miles off of the coast of Genoa, Italy. Having transferred 80,000 tonnes, she disconnected from the platform for a routine internal transfer operation, to allow oil to be pumped from two side-holds into a central one.

In later testimony, First Officer Donatos Lilis said: "I heard a very loud noise, like iron bars beating against each other. Perhaps the cover of a pump had broken. Then there was an awful explosion." Five crewmen died immediately, as fire broke out and oil started leaking from the hull as the plates overheated. As the fire engulfed the ship, flames rose 100m high, and after a series of further explosions occurred between 30-40,000 tons of oil poured into the sea.

The Italian authorities acted quickly, with hundreds of men fighting a fire which was difficult to access, and distributing more than six miles ofinflatablebarriers, submerged a metre below the surface, around the vessel to control the spillage. On day two, the Haven was to be towed close to the coast, in a bid to reduce the coastal area affected and make intervention easier. As the bow slipped beneath the surface, a steel cable was passed around the rudder and tugs applied towing pressure. But it was quickly clear that the ship had broken its keel, and the bow section came to rest in 450m of water. On 14 April, the 250m-long main body sank a mile and a half from the coast, between Arenzano and Varazze.

After the wreck was declared safe, a mini sub diver found that the stern section had grazed a rocky spur, though fortunately not hard enough to open any new holes in the hull, and come to rest at an angle on the flat, sandy seabed. He reported that most of the remaining 80,000 tons of crude had burnt or was at the surface. Most of the oil on the surface was able to be sucked up, and what remained below was in a solid state. For the next 12 years the Merranean coast of Italy and France was polluted, especially around Genoa and southern France.

 

Court Case

 

Background and Allegations

At the centre of the case was the allegation that Stelios Haji-Ioannou and his father Lucas Haji-Ioannou had kept their vessel, the Troodos-owned Cyprus-flagged Haven, in such disrepair that it blew up. According to news items it is also alleged that the tanker was scrapped after being hit by an Exocet missile during the Iran??raq War and should not have been put back into operation.2 Prosecutors had asked for seven-year sentences for manslaughter against both father and son. Christos Dovles, former director of the shipping firm for whom prosecutors had sought a sentence of two years and four months.

 

Charges

Lucas Haji-Ioannou, and his son Stelios Haji-Ioannou, faced charges of the manslaughter of the six killed, extortion and intimidating and attempting to bribe witnesses. Both denied the charges and pleaded not guilty.

 

Outcome

Despite the heavy charges levied against them, Stelios Haji-Ioannou and his father were later acquitted after three retrials (of which 2002 was the last) and much controversy, with subsequent appeals and demands for compensation were also thrown out.3 Stelios Hadjioannou was quoted after the trial: "My main comment is to ask why it took so long to clear innocent people of these terrible charges."4

 

Reception

Italy's Environment Ministry under-secretary at the time said he was "greatly embittered" by the verdict saying "The victims, the relatives and the marine environment that were all seriously damaged are left without convincing answers.1

The Italian president of the World Wildlife Fund (WWF), Grazia Francescato said in a statement that he was disgusted with Mr Haji-Ioannou's conduct and drew similarities with the then recent Moby Prince disaster and the acquittal of four men on charges of manslaughter in the ferry disaster off the Tuscan city of Livorno that killed 140 people in the same day of Haven's accident. 2

NUMAST, the union which represents merchant officers, described the acquittal as "depressing", a sentiment also expressed by the International Transport Workers' Federation (ITF). Only by making ship owners accountable for the state of vessels under their control would substandard ships be eliminated, Andrew Linington, head of communications at NUMAST said. "Even when ship owners were clearly linked with a ship that did not meet acceptable standards it seems no action will be taken," Linington said.3

 

Shipwreck

The Haven now lies at a depth of 33 to 83m off the coast of Genoa. It is claimed to be the largest shipwreck in the world and as with many old wrecks it is a popular tourist attraction with deep sea divers. 5

Whale Wars is a one-hour weekly American reality television series that premiered on November 7, 2008 on Animal Planet. The program follows Captain Paul Watson, founder of the Sea Shepherd Conservation Society, as he and his crew aboard the MV Steve Irwin attempt to deter Japanese ships that hunt minke and fin whales in the Southern Ocean Whale Sanctuary in the name of research.1

 

The theme song in the introduction is "Bullet with Butterfly Wings" by The Smashing Pumpkins.

 

Featured cast

The featured cast is mostly made up of officers and crew of the Sea Shepherd ship the MV Steve Irwin from the 2007/08 campaign in the Antarctic.

Name Position Notes
Paul Watson Captain Founder of the Sea Shepherd Conservation Society and co-founder of Greenpeace.
Peter Brown Officer - First Mate  
Peter Hammarstedt Officer - Second Mate  
Benjamin "Pottsy" Potts Chief Cook, Helicopter Assistant One of the two crewmembers who boarded a Japanese whaling vessel as part of an attempt to deliver a letter.
Dr. Scott Bell Doctor Treated two severe injuries.
Chris Aultman Recon Helicopter Pilot Left the mission before the second leg of the operation due to helicopter corrosion.
Giles Lane   Crewmember who accompanied Pottsy in boarding the Yushin Maru â„– 2 to deliver a letter.

 

Season synopsis

 

Animal Planet disclaimer

At the beginning of each episode and at times after breaks during the show, the following disclaimer from Animal Planet is displayed on screen to viewers:

The following program contains commentary and opinions that do not necessarily reflect the opinions of Animal Planet.

 

Season One

Season One consisted of seven episodes and aired from November 7, 2008 to December 19, 2008. Each episode premiered on Fridays at 9 PM E/P on Animal Planet.2 Much of the action depicted in this season occurred between January and March 2008. Season One is now available on DVD.3 In one commercial advertisement announcing the season premiere of the series on November 7 on Animal Planet, Sea Shepherd members on the shore of a beach parody the style of the 2008 presidential candidates' campaign ads, including the line "I'm Paul Watson, and I approve this message."


Episode # Episode Title Original U.S. Airdate
1 "Needle in a Haystack" November 7, 2008
Captain Paul Watson is allegedly shot by the Japanese whaling crew during a confrontation between the whaling factory ship Nisshin Maru and the Sea Shepherd vessel MV Steve Irwin. The episode then flashes back to the maiden launching and departure of the vessel from homeport three months earlier. 
2 "Nothing's Ideal" November 14, 2008
Giles Lane and Benjamin "Pottsy" Potts volunteer to board the Japanese whale catcher Yushin Maru â„– 2 without permission and were temporarily detained on the ship by the whaling crew. The incident received immediate attention from the international media. The MV Steve Irwin radios the Australian Federal Police under a charge of kidnapping, even though Lane and Potts boarded the vessel voluntarily and without permission. 
3 "International Incidents R Us" November 21, 2008
Without negotiation and confrontation with the MV Steve Irwin, the Yushin Maru â„– 2 agreed to transfer Pottsy and Giles to a government ship that would then meet with the Steve Irwin at a rendezvous point to return the two members. A leader decides to launch an attack on the Yushin Maru â„– 2 at dusk. Four crewmembers are sent on the Zodiacinflatable boatDelta to carry out the risky mission. After losing radio contact with them, recon pilot Chris Aultman, who was sent too late to survey the situation, reports that they are heading in the wrong direction and must return as night falls. The lone Delta was feared to be forever lost out in the middle of the dark, frigid, vast Antarctic Ocean. Fortunately, contact was finally made with the Delta, which eventually returns to the MV Steve Irwin over two hours later and behind schedule to retrieve Pottsy and Giles. 
4 "We Are Hooligans" November 28, 2008
Giles Lane and Ben Potts safely return to the MV Steve Irwin. The crew then discovers that an unknown ship, which was allegedly spying for the Japanese whaling fleet, has been following them, decides to recon it from behind a tabletop iceberg for any military personnel aboard, and temporarily drives it away after seeing no sign of illegal military activity. The crew later plans to ambush the mystery ship, soon identified as the Fukuyoshi â„– 68, to prevent information about the Steve Irwin's whereabouts from being given to the rest of the whaling fleet. They plan to do this by boarding the vessel and sabotaging its communication equipment, shutting off any communication with anyone. Before the mission, a hydraulic crane used to launch the motor rafts somehow got damaged, jeopardizing the Sea Shepherd's mission. 
5 "Doors Slamming and Things Breaking" December 5, 2008
The MV Steve Irwin experiences several technical difficulties, including a damaged engine, hydraulic crane, and helicopter. Running on only one engine, the ship must return to port at Melbourne, Australia to make repairs while the whaling continues. Some crewmembers decide to party and leave the operation. Upon arrival, they were welcomely greeted and cheered by the citizens, and by the police. Pottsy and Giles become instant celebrities on homecoming. After recruiting new members, the crew travels without its recon chopper and returns to the Southern Ocean only to shamefully find that the spy ship is still following them. 
6 "Ladies First" December 12, 2008
After noticing that the spy ship Fukuyoshi Maru â„– 68 has found and followed the MV Steve Irwin again, Captain Watson unsuccessfully attempts to send four female crewmembers to board the vessel to deliver a warrant. This leads to a man's injured thumb and a woman's injured pelvis. The Steve Irwin detects the Nisshin Maru on radar. At dusk, the entire ship experiences a power outage, leaving it drifting through an iceberg field without operating engines. 
7 "Boiling Point" December 19, 2008
After power was restored to part of the ship, the MV Steve Irwin finally finds, follows, and comes face to face two times with the Japanese whaling factory ship Nisshin Maru, which Watson considers the "most evil" vessel in international waters. A pod of whales swims between the two "warring" ships, which eventually engage in a ship-to-ship "battle." The captain of the Nisshin Maru warned on a recorded message sent multiple times through a horn that "If you dare board this vessel, you will be taken into custody." Recruited Sea Shepherds are the first to strike, throwing stink bombs with Butyric acid onto the decks of the Nisshin Maru, which dwarfed the Steve Irwin in size, while its crew watches and films the Steve Irwin. The Japanese whalers claim that three of their crewmembers were injured by the stink bombs. When the two ships meet the second time, the Steve Irwin crew strikes first again while the Nisshin Maru crew, in return, threatens to use tear gas grenades and throws flash bombs. Captain Watson allegedly survives a gunshot wound, in which he alleged that a bullet pierced his badge and was stopped by his bulletproof vest. The opposing sides each stand by and defend its own version of the incident. As the captain concluded that the second leg of the mission was successful, the Sea Shepherds claimed that they have saved about 500 whales. The Steve Irwin returns to Melbourne again before running out of fuel. 

 

Upcoming: Season Two

Animal Planet has announced that Season Two, called Whale Wars 2, will premiere in the summer of 2009. It is currently being filmed.

 

Critical reception

The critical reception has been generally positive for the show. Among adults aged 25-54, the series scored the highest viewer ratings in Animal Planet's history. 4

Review aggregation site MetaCritic has scored Whale Wars 71 out of 100 based on 6 reviews.5 Users of MetaCritic gave an average score of 5.6 out of 10.

Neil Genzlinger of the New York Times wrote 6:

Whale Wars splashes across the increasingly exhausted genre of people-at-work reality series like icy seawater, jolting you awake with a frothy, briny burst of―well, you get the idea. This is one spunky show.

Nancy Dewolf Smith of The Wall Street Journal wrote7 about Whale Wars:

What is shocking at first is how unprepared most of these people are for their self-appointed mission as planet savers. Although the word "deadly" is used often to underscore the risks the crew face, alone out in the wild Antarctic seas―their own incompetence can seem the most frightening.

Mary McNamara of The Los Angeles Times wrote8:

What makes Whale Wars different from a normal extreme career path-type show, is of course, the cause it is promoting. But more interesting is that murmuring beneath all the action is that age-old philosophic question: How far is too far in an undeniably just cause?

Criticism of the show has come largely from parties normally critical of Sea Shepherd. Specifically, the show has been criticized for not including a Japanese rebuttal to the claims of the Sea Shepherds.citation needed

 

Controversy

  Wikinews has related news: Protester_says_Japanese_whalers_shot_him
Further information: Paul Watson#Alleged shooting and Sea Shepherd Conservation Society#Operation Migaloo

Captain Paul Watson was allegedly shot by the Japanese crew or coast guard personnel during the campaign. The incident is heavily documented during the show in the final episode, and the first six episodes are covered as a buildup to what is portrayed as the major incident during the campaign.

The footage in Whale Wars shows Captain Watson standing on the deck of the Steve Irwin while Sea Shepherd crew throw stink bombs at the Nisshin Maru whaling vessel, while the Japanese respond by throwing Flashbang devices. Captain Watson is then shown reaching inside his jacket and bullet-proof vest and remarking "I've been hit."

Back inside the bridge of the Steve Irwin, a metal fragment is pulled from the vest, and the viewer is lead to believe that the bullet was stopped because of a vest, and a badge that the captain was wearing underneath it.910

Critics argue that Watson is extremely aware of the media war against the Japanese whalers, and just as the media reaction was his major justification for the earlier boarding of another Japanese ship by two of the Sea Shepherd crew members, the shooting incident had the same motive (ie. again being used as a tool to criticize the actions of the Japanese in the media).

According to an interview with Paul Watson11, it was reported by Reuters that Japan had informed Australia shots were fired during the standoff, but Japanese spokesmen later recanted the statement and denied any shots were fired while confirming that three "warning devices" (being the flashbangs) were thrown. 12 The Japanese later claimed that Paul Watson, the captain of the Steve Irwin, staged the incident in an attempt to win public and government sympathy and approval for the Sea Shepherd campaign.

 

See also

  • Southern Ocean Whale Sanctuary
  • Whaling in Japan
  • MV Steve Irwin
  • Nisshin Maru
  • Yushin Maru â„– 2
  • Operation Migaloo
  • Sea Shepherd Conservation Society
  • Greenpeace

 

 

A polyurethane, commonly abbreviated PU, is any polymer consisting of a chain of organic units joined by urethane (carbamate) links. Polyurethane polymers are formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst.

 

Polyurethane formulations cover an extremely wide range of stiffness, hardness, and densities. These materials include:

  • low density flexible foam used in upholstery and bedding,
  • low density rigid foam used for thermal insulation and e.g. automobile dashboards,
  • soft solid elastomers used for gel pads and print rollers, and
  • hard solid plastics used as electronic instrument bezels and structural parts.


Polyurethanes are widely used in high resiliency flexible foam seating, rigid foam insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and tires, automotive suspension bushings, electrical potting compounds, high performance adhesives and sealants e.g during asbestos removal works, Spandex fibres, seals, gaskets, carpet underlay, and hard plastic parts.

Polyurethane products are often called "urethanes". They should not be confused with the specific substance urethane, also known as ethyl carbamate. Polyurethanes are not produced from ethyl carbamate, nor do they contain it.

 

History

The pioneering work on polyurethane polymers was conducted by Otto Bayer and his coworkers in 1937 at the laboratories of I.G. Farben in Leverkusen, Germany.1 They recognized that using the polyaddition principle to produce polyurethanes from liquid diisocyanates and liquid polyether or polyester diols seemed to point to special opportunities, especially when compared to already existing plastics that were made by polymerizing olefins, or by polycondensation. The new monomer combination also circumvented existing patents obtained by Wallace Carothers on polyesters.2 Initially, work focused on the production of fibres and flexible foams. With development constrained by World War II (when PUs were applied on a limited scale as aircraft coating2), it was not until 1952 that polyisocyanates became commercially available. Commercial production of flexible polyurethane foam began in 1954, based on toluene diisocyanate (TDI) and polyester polyols. The invention of these foams (initially called imitation swiss cheese by the inventors2) was thanks to water accidentally introduced in the reaction mix. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibres were produced from hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO).

The first commercially available polyether polyol, poly(tetramethylene ether) glycol, was introduced by DuPont in 1956 by polymerizing tetrahydrofuran. Less expensive polyalkylene glycols were introduced by BASF and Dow Chemical the following year, 1957. These polyether polyols offered technical and commercial advantages such as low cost, ease of handling, and better hydrolytic stability; and quickly supplanted polyester polyols in the manufacture of polyurethane goods. Another early pioneer in PUs was the Mobay corporation.2 In 1960 more than 45,000 tons of flexible polyurethane foams were produced. As the decade progressed, the availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) heralded the development and use of polyurethane rigid foams as high performance insulation materials. Rigid foams based on polymeric MDI (PMDI) offered better thermal stability and combustion characteristics than those based on TDI. In 1967, urethane modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance to low density insulation products. Also during the 1960s, automotive interior safety components such as instrument and door panels were produced by back-filling thermoplastic skins with semi-rigid foam.

In 1969, Bayer AG exhibited an all plastic car in Dusseldorf, Germany. Parts of this car were manufactured using a new process called RIM, Reaction Injection Molding. RIM technology uses high-pressure impingement of liquid components followed by the rapid flow of the reaction mixture into a mold cavity. Large parts, such as automotive fascia and body panels, can be molded in this manner. Polyurethane RIM evolved into a number of different products and processes. Using diamine chain extenders and trimerization technology gave poly(urethane urea), poly(urethane isocyanurate), and polyurea RIM. The addition of fillers, such as milled glass, mica, and processed mineral fibres gave arise to RRIM, reinforced RIM, which provided improvements in flexural modulus (stiffness) and thermal stability. This technology allowed production of the first plastic-body automobile in the United Sates, the Pontiac Fiero, in 1983. Further improvements in flexural modulus were obtained by incorporating preplaced glass mats into the RIM mold cavity, also known as SRIM, or structural RIM.

Starting in the early 1980s, water-blown microcellular flexible foam was used to mold gaskets for panel and radial seal air filters in the automotive industry. Since then, increasing energy prices and the desire to eliminate PVC plastisol from automotive applications have greatly increased market share. Costlier raw materials are offset by a significant decrease in part weight and in some cases, the elimination of metal end caps and filter housings. Highly filled polyurethane elastomers, and more recently unfilled polyurethane foams are now used in high-temperature oil filter applications.

Polyurethane foam (including foam rubber) is often made by adding small amounts of volatile materials, so-called blowing agents, to the reaction mixture. These simple volatile chemicals yield important performance characteristics, primarily thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol led to the greatly reduced use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). Other haloalkanes, such as the hydrochlorofluorocarbon 1,1-dichloro-1-fluoroethane (HCFC-141b), were used as interim replacements until their phase out under the IPPC directive on greenhouse gases in 1994 and by the Volatile Organic Compounds (VOC) directive of the EU in 1997 (See: Haloalkanes). By the late 1990s, the use of blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) became more widespread in North America and the EU, although chlorinated blowing agents remained in use in many developing countries.3

Building on existing polyurethane spray coating technology and polyetheramine chemistry, extensive development of two-component polyurea spray elastomers took place in the 1990s. Their fast reactivity and relative insensitivity to moisture make them useful coatings for large surface area projects, such as secondary containment, manhole and tunnel coatings, and tank liners. Excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. During the same period, new two-component polyurethane and hybrid polyurethane-polyurea elastomer technology was used to enter the marketplace of spray-in-place load bed liners. This technique for coating pickup truck beds and other cargo bays creates a durable, abrasion resistant composite with the metal substrate, and eliminates corrosion and brittleness associated with drop-in thermoplastic bed liners.

The use of polyols derived from vegetable oils to make polyurethane products began garnering attention beginning around 2004, partly due to the rising costs of petrochemical feedstocks and partially due to an enhanced public desire for environmentally friendly green products.4 One of the most vocal supporters of these polyurethanes made using natural oil polyols is the Ford Motor Company.5

 

Chemistry

generalized polyurethane reaction
 

Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, and phenolics.678910 A urethane linkage is produced by reacting an isocyanate group, -N=C=O with a hydroxyl (alcohol) group, -OH. Polyurethanes are produced by the polyaddition reaction of a polyisocyanate with a polyalcohol (polyol) in the presence of a catalyst and other additives. In this case, a polyisocyanate is a molecule with two or more isocyanate functional groups, R-(N=C=O)n ≥ 2 and a polyol is a molecule with two or more hydroxyl functional groups, R'-(OH)n ≥ 2. The reaction product is a polymer containing the urethane linkage, -RNHCOOR'-. Isocyanates will react with any molecule that contains an active hydrogen. Importantly, isocyanates react with water to form a urea linkage and carbon dioxide gas; they also react with polyetheramines to form polyureas. Commercially, polyurethanes are produced by reacting a liquid isocyanate with a liquid blend of polyols, catalyst, and other additives. These two components are referred to as a polyurethane system, or simply a system. The isocyanate is commonly referred to in North America as the 'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as the 'B-side' or as the 'poly'. This mixture might also be called a 'resin' or 'resin blend'. In Europe the meanings for 'A-side' and 'B-side' are reversed. Resin blend additives may include chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and fillers.

The first essential component of a polyurethane polymer is the isocyanate. Molecules that contain two isocyanate groups are called diisocyanates. These molecules are also referred to as monomers or monomer units, since they themselves are used to produce polymeric isocyanates that contain three or more isocyanate functional groups. Isocyanates can be classed as aromatic, such as diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI); or aliphatic, such as hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). An example of a polymeric isocyanate is polymeric diphenylmethane diisocyanate, which is a blend of molecules with two-, three-, and four- or more isocyanate groups, with an average functionality of 2.7. Isocyanates can be further modified by partially reacting them with a polyol to form a prepolymer. A quasi-prepolymer is formed when the stoichiometric ratio of isocyanate to hydroxyl groups is greater than 2:1. A true prepolymer is formed when the stoichiometric ratio is equal to 2:1. Important characteristics of isocyanates are their molecular backbone, % NCO content, functionality, and viscosity.

The second essential component of a polyurethane polymer is the polyol. Molecules that contain two hydroxyl groups are called diols, those with three hydroxyl groups are called triols, et cetera. In practice, polyols are distinguished from short chain or low-molecular weight glycol chain extenders and cross linkers such as ethylene glycol (EG), 1,4-butanediol (BDO), diethylene glycol (DEG), glycerine, and trimethylol propane (TMP). Polyols are polymers in their own right. They are formed by base-catalyzed addition of propylene oxide (PO), ethylene oxide (EO) onto a hydroxyl or amine containing initiator, or by polyesterification of a di-acid, such as adipic acid, with glycols, such as ethylene glycol or dipropylene glycol (DPG). Polyols extended with PO or EO are polyether polyols. Polyols formed by polyesterification are polyester polyols. The choice of initiator, extender, and molecular weight of the polyol greatly affect its physical state, and the physical properties of the polyurethane polymer. Important characteristics of polyols are their molecular backbone, initiator, molecular weight, % primary hydroxyl groups, functionality, and viscosity.

PU reaction mechanism catalyzed by a tertiary amine
 
carbon dioxide gas formed by reacting water and isocyanate
 

The polymerization reaction is catalyzed by tertiary amines, such as dimethylcyclohexylamine, and organometallic compounds, such as dibutyltin dilaurate or bismuth octanoate. Furthermore, catalysts can be chosen based on whether they favor the urethane (gel) reaction, such as 1,4-diazabicyclo2.2.2octane (also called DABCO or TEDA), or the urea (blow) reaction, such as bis-(2-dimethylaminoethyl)ether, or specifically drive the isocyanate trimerization reaction, such as potassium octoate.

One of the most desirable attributes of polyurethanes is their ability to be turned into foam. Blowing agents such as water, certain halocarbons such as HFC-245fa (1,1,1,3,3-pentafluoropropane) and HFC-134a (1,1,1,2-tetrafluoroethane), and hydrocarbons such as n-pentane, can be incorporated into the poly side or added as an auxiliary stream. Water reacts with the isocyanate to create carbon dioxide gas, which fills and expands cells created during the mixing process. The reaction is a three step process. A water molecule reacts with an isocyanate group to form a carbamic acid. Carbamic acids are unstable, and decompose forming carbon dioxide and an amine. The amine reacts with more isocyanate to give a substituted urea. Water has a very low molecular weight, so even though the weight percent of water may be small, the molar proportion of water may be high and considerable amounts of urea produced. The urea is not very soluble in the reaction mixture and tends to form separate "hard segment" phases consisting mostly of polyurea. The concentration and organization of these polyurea phases can have a significant impact on the properties of the polyurethane foam.11 Halocarbons and hydrocarbons are chosen such that they have boiling points at or near room temperature. Since the polymerization reaction is exothermic, these blowing agents volatilize into a gas during the reaction process. They fill and expand the cellular polymer matrix, creating a foam. It is important to know that the blowing gas does not create the cells of a foam. Rather, foam cells are a result of blowing gas diffusing into bubbles that are nucleated or stirred into the system at the time of mixing. In fact, high density microcellular foams can be formed without the addition of blowing agents by mechanically frothing or nucleating the polyol component prior to use.

Surfactants are used to modify the characteristics of the polymer during the foaming process. They are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and surface defects. Rigid foam surfactants are designed to produce very fine cells and a very high closed cell content. Flexible foam surfactants are designed to stabilize the reaction mass while at the same time maximizing open cell content to prevent the foam from shrinking. The need for surfactant can be affected by choice of isocyanate, polyol, component compatibility, system reactivity, process conditions and equipment, tooling, part shape, and shot weight.

 

Raw materials

For the manufacture of polyurethane polymers, two groups of at least bifunctional substances are needed as reactants; compounds with isocyanate groups, and compounds with active hydrogen atoms. The physical and chemical character, structure, and molecular size of these compounds influence the polymerization reaction, as well as ease of processing and final physical properties of the finished polyurethane. In addition, additive such as catalysts, surfactants, blowing agents, cross linkers, flame retardants, light stabilizers, and fillers are used to control and modify the reaction process and performance characteristics of the polymer.

 

Isocyanates

Isocyanates with two or more functional groups are required for the formation of polyurethane polymers. Volume wise, aromatic isocyanates account for the vast majority of global diisocyanate production. Aliphatic and cycloaliphatic isocyanates are also important building blocks for polyurethane materials, but in much smaller volumes. There are a number of reasons for this. First, the aromatically linked isocyanate group is much more reactive than the aliphatic one. Second, aromatic isocyanates are more economical to use. Aliphatic isocyanates are used only if special properties are required for the final product. For example, light stable coatings and elastomers can only be obtained with aliphatic isocyanates. Even within the same class of isocyanates, there is a significant difference in reactivity of the functional groups based on steric hindrance. In the case of 2,4-toluene diisocyanate, the isocyanate group in the para position to the methyl group is much more reactive than the isocyanate group in the ortho position.

Phosgenation of corresponding amines is the main technical process for the manufacture of isocyanates. The amine raw materials are generally manufactured by the hydrogenation of corresponding nitro compounds. For example, toluenediamine (TDA) is manufactured from dinitrotoluene, which then converted to toluene diisocyanate (TDI). Diamino diphenylmethane or methylenedianiline (MDA) is manufactured from nitrobenzene via aniline, which is then converted to diphenylmethane diisocyanate (MDI).

The two most important aromatic isocyanates are toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). TDI consists of a mixture of the 2,4- and 2,6-diisocyanatotoluene isomers. The most important product is TDI-80 (TD-80), consisting of 80% of the 2,4-isomer and 20% of the 2,6-isomer. This blend is used extensively in the manufacture of polyurethane flexible slabstock and molded foam.12 TDI, and especially crude TDI and TDI/MDI blends can be used in rigid foam applications, but have been supplanted by polymeric MDI. TDI-polyether and TDI-polyester prepolymers are used in high performance coating and elastomer applications. Prepolymers are available that have been vacuum stripped of TDI monomer, which greatly reduces their toxicity. Diphenylmethane diisocyanate (MDI) has three isomers, 4,4'-MDI, 2,4'-MDI, and 2,2'-MDI, and is also polymerized to provide oligomers of functionality three and higher.

Only the 4,4'-MDI monomer is sold commercially as a single isomer. It is provided either as a frozen solid or flake, or in molten form, and is used to manufacture high performance prepolymers. Monomer blends, consisting of approximately 50% of the 4,4'-isomer and 50% of the 2,4'-isomer, are liquid at room temperature and are used to manufacture prepolymers for polyurea spray elastomer applications. 4,4'-MDI blends containing MDI uretonimine, carbodiimide, and allophonate moieties are also liquid at room temperature, and are used in the manufacture of integral skin and microcellular foams. 4,4'-MDI-glycol prepolymers offer increased mechanical properties in the same applications, but are prone to freezing at temperatures below 20°C. Polymeric MDI (PMDI) is used in rigid pour-in-place, spray foam, and molded foam applications. Polymeric MDI that contains a very high portion of high-functionality oligomers is used to manufacture polyurethane and polyisocyanurate rigid insulation boardstock. Modified PMDI, which contains high levels of MDI monomer, is used in the production of polyurethane flexible molded and microcellular foam. The relative percentage of the 4,4'- and 2,4'- isomers is adjusted to change the reactivity and storage stability of the isocyanate blend, as well as the firmness and other physical properties of the finished goods. Other aromatic isocyanate include p-phenylene diisocyante (PPDI), naphthalene diisocyanate (NDI), and o-tolidine diisocyanate (TODI).

The most important aliphatic and cycloaliphatic isocyanates are 1,6-hexamethylene diisocyanate (HDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), and 4,4'-diisocyanato dicyclohexylmethane (H12MDI). They are used to produce light stable, non-yellowing polyurethane coatings and elastomers. Because of their toxicity, aliphatic isocyanate monomers are converted into prepolymers, biurets, dimers, and trimers for commercial use. HDI adducts are used extensively for weather and abrasion resistant coatings and lacquers. IPDI is used in the manufacture of coatings, elastomeric adhesives and sealants. H12MDI prepolymers are used to produce high performance coatings and elastomers with optical clarity and hydrolysis resistance. Other aliphatic isocyanates include cyclohexane diisocyanate (CHDI), tetramethylxylene diisocyanate (TMXDI), and 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI).

 

Polyols

Polyols are higher molecular weight materials manufactured from an initiator and monomeric building blocks. They are most easily classified as polyether polyols, which are made by the reaction of epoxides (oxiranes) with an active hydrogen containing starter compounds, or polyester polyols, which are made by the polycondensation of multifunctional carboxylic acids and hydroxyl compounds. They can be further classified according to their end use as flexible or rigid polyols, depending on the functionality of the initiator and their molecular weight. Taking into account functionality, flexible polyols have molecular weights from 2,000 to 10,000 (OH# from 18 to 56). Rigid polyols have molecular weights from 250 to 700 (OH# from 300 to 700). Polyols with molecular weights from 700 to 2,000 (OH# 60 to 280) are used to add stiffness or flexibility to base systems, as well as increase solubility of low molecular weight glycols in high molecular weight polyols.

Polyether polyols come in a wide variety of grades based on their end use, but are all constructed in a similar manner. Polyols for flexible applications use low functionality initiators such as dipropylene glycol (f=2) or glycerine (f=3). Polyols for rigid applications use high functionality initiators such sucrose (f=8), sorbitol (f=6), toluenediamine (f=4), and Mannich bases (f=4). Propylene oxide is then added to the initiators until the desired molecular weight is achieved. Polyols extended with propylene oxide are terminated with secondary hydroxyl groups. In order to change the compatibility, rheological properties, and reactivity of a polyol, ethylene oxide is used as a co-reactant to create random or mixed block heteropolymers. Polyols capped with ethylene oxide contain a high percentage of primary hydroxyl groups, which are more reactive than secondary hydroxyl groups. Because of their high viscosity (470 OH# sucrose polyol, 33,000 cps at 25°C), carbohydrate initiated polyols often use glycerine or diethylene glycol as a co-initiate in order to lower the viscosity to ease handling and processing (490 OH# sucrose-glycerine polyol, 5,500 cps at 25°C). Graft polyols (also called filled polyols or polymer polyols) contain finely dispersed styrene-acrylonitrile, acrylonitrile, or polyurea (PHD) polymer solids chemically grafted to a high molecular weight polyether backbone. They are used to increase the load bearing properties of low density high-resiliency (HR) foam, as well as add toughness to microcellular foams and cast elastomers. PHD polyols are also used to modify the combustion properties of HR flexible foam. Solids content ranges from 14% to 50%, with 22% and 43% being typical. Initiators such as ethylenediamine and triethanolamine are used to make low molecular weight rigid foam polyols that have built-in catalytic activity due to the presence of nitrogen atoms in the backbone. They are used to increase system reactivity and physical property build, and to reduce the friability of rigid foam molded parts. A special class of polyether polyols, poly(tetramethylene ether) glycols are made by polymerizing tetrahydrofuran. They are used in high performance coating and elastomer applications.

Polyester polyols fall into two distinct categories according to composition and application. Conventional polyester polyols are based on virgin raw materials and are manufactured by the direct polyesterification of high-purity diacids and glycols, such as adipic acid and 1,4-butanediol. They are distinguished by the choice of monomers, molecular weight, and degree of branching. While costly and difficult to handle because of their high viscosity, they offer physical properties not obtainable with polyether polyols, including superior solvent, abrasion, and cut resistance. Other polyester polyols are based on reclaimed raw materials. They are manufactured by transesterification (glycolysis) of recycled poly(ethyleneterephthalate) (PET) or dimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol. These low molecular weight, aromatic polyester polyols are used in the manufacture of rigid foam, and bring low cost and excellent flammability characteristics to polyisocyanurate (PIR) boardstock and polyurethane spray foam insulation.

Specialty polyols include polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols, and polysulfide polyols. The materials are used in elastomer, sealant, and adhesive applications that require superior weatherability, and resistance to chemical and environmental attack. Natural oil polyols derived from castor oil and other vegetable oils are used to make elastomers, flexible bunstock, and flexible molded foam.

 

Chain extenders and cross linkers

Chain extenders (f=2) and cross linkers (f=3 or greater) are low molecular weight hydroxyl and amine terminated compounds that play an important role in the polymer morphology of polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams. The elastomeric properties of these materials are derived from the phase separation of the hard and soft copolymer segments of the polymer, such that the urethane hard segment domains serve as cross-links between the amorphous polyether (or polyester) soft segment domains. This phase separation occurs because the mainly non-polar, low melting soft segments are incompatible with the polar, high melting hard segments. The soft segments, which are formed from high molecular weight polyols, are mobile and are normally present in coiled formation, while the hard segments, which are formed from the isocyanate and chain extenders, are stiff and immobile. Because the hard segments are covalently coupled to the soft segments, they inhibit plastic flow of the polymer chains, thus creating elastomeric resiliency. Upon mechanical deformation, a portion of the soft segments are stressed by uncoiling, and the hard segments become aligned in the stress direction. This reorientation of the hard segments and consequent powerful hydrogen bonding contributes to high tensile strength, elongation, and tear resistance values.1314151617 The choice of chain extender also determines flexural, heat, and chemical resistance properties. The most important chain extenders are ethylene glycol, 1,4-butanediol (1,4-BDO or BDO), 1,6-hexanediol, cyclohexane dimethanol and hydroquinone bis(2-hydroxyethyl) ether (HQEE). All of these glycols form polyurethanes that phase separate well and form well defined hard segment domains, and are melt processable. They are all suitable for thermoplastic polyurethanes with the exception of ethylene glycol, since its derived bis-phenyl urethane undergoes unfavorable degradation at high hard segment levels.18 Diethanolamine and triethanolamine are used in flex molded foams to build firmness and add catalytic activity. Diethyltoluenediamine is used extensively in RIM, and in polyurethane and polyurea elastomer formulations.

table of chain extenders and cross linkers 19
hydroxyl compounds ? difunctional molecules
  MW s.g. m.p. °C b.p. °C
ethylene glycol 62.1 1.110 -13.4 197.4
diethylene glycol 106.1 1.111 -8.7 245.5
triethylene glycol 150.2 1.120 -7.2 287.8
tetraethylene glycol 194.2 1.123 -9.4 325.6
propylene glycol 76.1 1.032 supercools 187.4
dipropylene glycol 134.2 1.022 supercools 232.2
tripropylene glycol 192.3 1.110 supercools 265.1
1,3-propanediol 76.1 1.060 -28 210
1,3-butanediol 92.1 1.005 - 207.5
1,4-butanediol 92.1 1.017 20.1 235
neopentyl glycol 104.2 - 130 206
1,6-hexanediol 118.2 1.017 43 250
1,4-cyclohexanedimethanol - - - -
HQEE - - - -
ethanolamine 61.1 1.018 10.3 170
diethanolamine 105.1 1.097 28 271
methyldiethanolamine 119.1 1.043 -21 242
phenyldiethanolamine 181.2 - 58 228
hydroxyl compounds ? trifunctional molecules
  MW s.g. f.p. °C b.p. °C
glycerol 92.1 1.261 18.0 290
trimethylolpropane - - - -
1,2,6-hexanetriol - - - -
triethanolamine 149.2 1.124 21 -
hydroxyl compounds ? tetrafunctional molecules
  MW s.g. m.p. °C b.p. °C
pentaerythritol 136.2 - 260.5 -
N,N,N',N'-tetrakis
(2-hydroxypropyl)
ethylenediamine
- - - -
amine compounds ? difunctional molecules
  MW s.g. m.p. °C b.p. °C
diethyltoluenediamine 178.3 1.022 - 308
dimethylthiotoluenediamine 214.0 1.208 - -

 

Catalysts

Polyurethane catalysts can be classified into two broad categories, amine compounds and organometallic complexes. They can be further classified as to their specificity, balance, and relative power or efficiency. Traditional amine catalysts have been tertiary amines such as triethylenediamine (TEDA, also known as 1,4-diazabicyclo2.2.2octane or DABCO), dimethylcyclohexylamine (DMCHA), and dimethylethanolamine (DMEA). Tertiary amine catalysts are selected based on whether they drive the urethane (polyol+isocyanate, or gel) reaction, the urea (water+isocyanate, or blow) reaction, or the isocyanate trimerization reaction. Since most tertiary amine catalysts will drive all three reactions to some extent, they are also selected based on how much they favor one reaction over another. For example, tetramethylbutanediamine (TMBDA) preferentially drives the gel reaction over the blow reaction. On the other hand, both pentamethyldipropylenetriamine and N-(3-dimethylaminopropyl)-N,N-diisopropanolamine balance the blow and gel reactions, although the former is more potent than the later on a weight basis. 1,3,5-(tris(3-dimethylamino)propyl)-hexahydro-s-triazine is a trimerization catalyst that also strongly drives the blow reaction. Molecular structure gives some clue to the strength and selectivity of the catalyst. Blow catalysts generally have an ether linkage two carbons away from a tertiary nitrogen. Examples include bis-(2-dimethylaminoethyl)ether and N-ethylmorpholine. Strong gel catalysts contain alkyl-substituted nitrogens, such as triethylamine (TEA), 1,8-diazabicyclo5.4.0undecene-7 (DBU), and pentamethyldiethylenetriamine (PMDETA). Weaker gel catalysts contain ring-substituted nitrogens, such as benzyldimethylamine (BDMA). Trimerization catalysts contain the triazine structure, or are quaternary ammonium salts. Two trends have emerged since the late 1980s. The requirement to fill large, complex tooling with increasing production rates has led to the use of blocked catalysts to delay front end reactivity while maintaining back end cure. In the United States, acid- and quaternary ammonium salt-blocked TEDA and bis-(2-dimethylaminoethyl)ether are common blocked catalysts used in molded flexible foam and microcellular integral skin foam applications. Increasing aesthetic and environmental awareness has led to the use of non-fugitive catalysts for vehicle interior and furnishing applications in order to reduce odor, fogging, and the staining of vinyl coverings. Catalysts that contain a hydroxyl group or an active amino hydrogen, such as N,N,N'-trimethyl-N'-hydroxyethyl-bis(aminoethyl)ether and N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine that react into the polymer matrix can replace traditional catalysts in these applications.2021

Organometallic compounds based on mercury, lead, tin (dibutyltin dilaurate), bismuth (bismuth octanoate), and zinc are used as polyurethane catalysts. Mercury carboxylates, such as phenylmercuric neodeconate, are particularly effective catalysts for polyurethane elastomer, coating and sealant applications, since they are very highly selective towards the polyol+isocyanate reaction. Mercury catalysts can be used at low levels to give systems a long pot life while still giving excellent back-end cure. Lead catalysts are used in highly reactive rigid spray foam insulation applications, since they maintain their potency in low-temperature and high-humidity conditions. Due to their toxicity and the necessity to dispose of mercury and lead catalysts and catalyzed material as hazardous waste in the United States, formulators have been searching for suitable replacements. Since the 1990s, bismuth and zinc carboxylates have been used as alternatives but have short comings of their own. In elastomer applications, long pot life systems do not build green strength as fast as mercury catalyzed systems. In spray foam applications, bismuth and zinc do not drive the front end fast enough in cold weather conditions and must be otherwise augmented to replace lead. Alkyl tin carboxylates, oxides and mercaptides oxides are used in all types of polyurethane applications. For example, dibutyltin dilaurate is a standard catalyst for polyurethane adhesives and sealants, dioctyltin mercaptide is used in microcellular elastomer applications, and dibutyltin oxide is used in polyurethane paint and coating applications. Tin mercaptides are used in formulations that contain water, as tin carboxylates are susceptible to degradation from hydrolysis.2223

 

Surfactants

Surfactants are used to modify the characteristics of both foam and non-foam polyurethane polymers. They take the form of polydimethylsiloxane-polyoxyalkylene block copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. In foams, they are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and sub-surface voids. In non-foam applications they are used as air release and anti-foaming agents, as wetting agents, and are used to eliminate surface defects such as pin holes, orange peel, and sink marks.

 

Production

The main polyurethane producing reaction is between a diisocyanate (aromatic and aliphatic types are available) and a polyol, typically a polypropylene glycol or polyester polyol, in the presence of catalysts and materials for controlling the cell structure, (surfactants) in the case of foams. Polyurethane can be made in a variety of densities and hardnesses by varying the type of monomer(s) used and adding other substances to modify their characteristics, notably density, or enhance their performance. Other additives can be used to improve the fire performance, stability in difficult chemical environments and other properties of the polyurethane products.

Though the properties of the polyurethane are determined mainly by the choice of polyol, the diisocyanate exerts some influence, and must be suited to the application. The cure rate is influenced by the functional group reactivity and the number of functional isocyanate groups. The mechanical properties are influenced by the functionality and the molecular shape. The choice of diisocyanate also affects the stability of the polyurethane upon exposure to light. Polyurethanes made with aromatic diisocyanates yellow with exposure to light, whereas those made with aliphatic diisocyanates are stable.24

Softer, elastic, and more flexible polyurethanes result when linear difunctional polyethylene glycol segments, commonly called polyether polyols, are used to create the urethane links. This strategy is used to make spandex elastomeric fibers and soft rubber parts, as well as foam rubber. More rigid products result if polyfunctional polyols are used, as these create a three-dimensional cross-linked structure which, again, can be in the form of a low-density foam.

An even more rigid foam can be made with the use of specialty trimerization catalysts which create cyclic structures within the foam matrix, giving a harder, more thermally stable structure, designated as polyisocyanurate foams. Such properties are desired in rigid foam products used in the construction sector.

Careful control of viscoelastic properties ― by modifying the catalysts and polyols used ―can lead to memory foam, which is much softer at skin temperature than at room temperature.

There are then two main foam variants: one in which most of the foam bubbles (cells) remain closed, and the gas(es) remains trapped, the other being systems which have mostly open cells, resulting after a critical stage in the foam-making process (if cells did not form, or became open too soon, foam would not be created). This is a vitally important process: if the flexible foams have closed cells, their softness is severely compromised, they become pneumatic in feel, rather than soft; so, generally speaking, flexible foams are required to be open-celled.

The opposite is the case with most rigid foams. Here, retention of the cell gas is desired since this gas (especially the fluorocarbons referred to above) gives the foams their key characteristic: high thermal insulation performance.

A third foam variant, called microcellular foam, yields the tough elastomeric materials typically experienced in the coverings of car steering wheels and other interior automotive components.

 

Health and safety

Fully reacted polyurethane polymer, CAS # 9009-54-5 (CAS registry number), is chemically inert. In the United States, no exposure limits have been established by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA for carcinogenicity. Polyurethane polymer is a combustible solid and will ignite if exposed to an open flame for a sufficient period of time. Decomposition products include carbon monoxide, oxides of nitrogen, and hydrogen cyanide. Firefighters should wear self-contained breathing apparatus in enclosed areas. When heated above about 200°C the PU polymer will thermally degrade and emit not only the isocyanates it was made from but also a number of mono isocyanates like methyl isocyanate (MIC) and isocyanic acid (ICA), depending on the type of PU being heated. Heating of any PU material (e. g. soft foam, paint dust after sanding, textiles, PU painted flooring etc.) should be avoided at any cost. Polyurethane polymer dust can cause mechanical irritation to the eyes and lungs. Proper hygiene controls and personal protective equipment (PPE), such as gloves, dust masks, respirators, mechanical ventilation, and protective clothing and eye wear should be used. Clothes should be changed and hands, hair and face should be cleaned before smoking.

Liquid resin blends and isocyanates may contain hazardous or regulated components. They should be handled in accordance with manufacturer recommendations found on product labels, and in MSDS (Material Safety Data Sheet) and product technical literature. Isocyanates are known skin and respiratory sensitizers, and proper engineering controls should be in place to prevent exposure to isocyanate liquid and vapor.

In the United States, additional health and safety information can be found through organizations such as the Polyurethane Manufacturers Association (PMA) and the Center for the Polyurethanes Industry (CPI), as well as from polyurethane system and raw material manufacturers. In Europe, health and safety information is available from ISOPA25, the European Diisocyanate and Polyol Producers Association. Regulatory information can be found in the Code of Federal Regulations Title 21 (Food and Drugs) and Title 40 (Protection of the Environment).

 

Uses

characteristics of polyurethane materials
 

Polyurethane products have many uses. Over three quarters of the global consumption of polyurethane products is in the form of foams, with flexible and rigid types being roughly equal in market size. In both cases, the foam is usually behind other materials: flexible foams are behind upholstery fabrics in commercial and domestic furniture; rigid foams are inside the metal and plastic walls of most refrigerators and freezers, or behind paper, metals and other surface materials in the case of thermal insulation panels in the construction sector. Its use in garments is growing: for example, in lining the cups of brassieres. Polyurethane is also used for moldings which include door frames, columns, balusters, window headers, pediments, medallions and rosettes.

Polyurethane is also used in the concrete construction industry to create formliners. Polyurethane formliners serves as a mold for concrete, creating a variety of textures and art.

The precursors of expanding polyurethane foam are available in many forms, for use in insulation, sound deadening, flotation, industrial coatings, packing material, and even cast-in-place upholstery padding. Since they adhere to most surfaces and automatically fill voids, they have become quite popular in these applications.

The following table shows how polyurethanes are used (US data from 2004):26.

Application Amount of polyurethane used

(millions of pounds)

Percentage of total
Building & Construction 1,459 26.8%
Transportation 1,298 23.8%
Furniture & Bedding 1,127 20.7%
Appliances 278 5.1%
Packaging 251 4.6%
Textiles, Fibers & Apparel 181 3.3%
Machinery & Foundry 178 3.3%
Electronics 75 1.4%
Footwear 39 0.7%
Other uses 558 10.2%
Total 5,444 100.0%

In 2007, the global consumption of polyurethane raw materials was above 12 million metric tons, the average annual growth rate is about 5%. 27

 

Varnish

Polyurethane materials are commonly formulated as paints and varnishes for finishing coats to protect or seal wood. This use results in a hard, abrasion-resistant, and durable coating that is popular for hardwood floors, but considered by some to be difficult or unsuitable for finishing furniture or other detailed pieces. Relative to oil or shellac varnishes, polyurethane varnish forms a harder film which tends to de-laminate if subjected to heat or shock, fracturing the film and leaving white patches. This tendency increases when it is applied over softer woods like pine. This is also in part due to polyurethane's lesser penetration into the wood. Various priming techniques are employed to overcome this problem, including the use of certain oil varnishes, specified "dewaxed" shellac, clear penetrating epoxy, or "oil-modified" polyurethane designed for the purpose. Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher "build" of film, accomplishing in two coats what may require multiple applications of oil. Polyurethane may also be applied over a straight oil finish, but because of the relatively slow curing time of oils, the presence of volatile byproducts of curing, and the need for extended exposure of the oil to oxygen, care must be taken that the oils are sufficiently cured to accept the polyurethane.

Unlike drying oils and alkyds which cure, after evaporation of the solvent, upon reaction with oxygen from the air, polyurethane coatings cure after evaporation of the solvent by a variety of reactions of chemicals within the original mix, or by reaction with moisture from the air. Certain products are "hybrids" and combine different aspects of their parent components. "Oil-modified" polyurethanes, whether water-borne or solvent-borne, are currently the most widely used wood floor finishes.

Exterior use of polyurethane varnish may be problematic due to its susceptibility to deterioration through ultra-violet light exposure. It must be noted, however, that all clear or transluscent varnishes, and indeed all film-polymer coatings (i.e.paint, stain, epoxy, synthetic plastic, etc.) are susceptible to this damage in varying degrees. Pigments in paints and stains protect against UV damage, while UV-absorbers are added to polyurethane and other varnishes (in particular "spar" varnish) to work against UV damage. Polyurethanes are typically the most resistant to water exposure, high humidity, temperature extremes, and fungus or mildew, which also adversely affect varnish and paint performance.

 

Wheels

Polyurethane is also used in making solid tires. Industrial applications include forklift drive and load wheels, grocery cart and, rollercoaster wheels. Modern roller blading and skateboarding became economical only with the introduction of tough, abrasion-resistant polyurethane parts, helping to usher in the permanent popularity of what had once been an obscure 60s craze. The durability of Polyurethane wheel allowed the range of tricks and stunts performed on skateboards to expand considerably. Other constructions have been developed for pneumatic tires, and microcellular foam variants are widely used in tires on wheelchairs, bicycles and other such uses. These latter foam types are also widely encountered in car steering wheels and other interior and exterior automotive parts, including bumpers and fenders.

Industrial Polyurethane Applications

 

Furniture

Open cell flexible polyurethane foam (FPF) is made by mixing polyols, diisocyanates, catalysts, auxiliary blowing agents and other additives and allowing the resulting foam to rise freely. Most FPF is manufactured using continuous processing technology and also can be produced in batches where relatively small blocks of foam are made in open-topped molds, boxes, or other suitable enclosurers. The foam is then cut to the desired shape and size for use in a variety of furniture and furnishings applications.

Applications for flexible polyurethane foam include upholstered furniture cushions, automotive seat cushions and interior trim, carpet cushion, and mattress padding and solid-core mattress cores.

Flexible polyurethane foam is a recyclable product. 28

 

Automobile seats

Flexible and semi-flexible polyurethane foams are used extensively for interior components of automobiles, in seats, headrests, armrests, roof liners, dashboards and instrument panels.

Polyurethane foam in the lower half of the mold in which it was made. When assembled into a car seat, this foam makes up the seat back. The forward-facing part of the seat back is the surface of the foam which is face-down in the mold. The two holes in the foam at the top of the picture are for the headrest posts.
Foam after removal from the mold.

Polyurethanes are used to make automobile seats in a remarkable manner. The seat manufacturer has a mold for each seat model. The mold is a closeable "clamshell" sort of structure that will allow quick casting of the seat cushion, so-called molded flexible foam, which is then upholstered after removal from the mold.

It is possible to combine these two steps, so-called in-situ, foam-in-fabric or direct moulding. A complete, fully-assembled seat cover is placed in the mold and held in place by vacuum drawn through small holes in the mold. Sometimes a thin pliable plastic film backing on the fabric is used to help the vacuum work more effectively. The metal seat frame is placed into the mold and the mold closed. At this point the mold contains what could be visualized as a "hollow seat", a seat fabric held in the correct position by the vacuum and containing a space with the metal frame in place.

Polyurethane chemicals are injected by a mixing head into the mold cavity. Then the mold is held at a preset reaction temperature until the chemical mixture has foamed, filled the mold, and formed a stable soft foam. The time required is two to three minutes, depending on the size of the seat and the precise formulation and operating conditions. Then the mold is usually opened slightly for a minute or two for an additional cure time, before the fully upholstered seat is removed.

 

Houses, sculptures, and decorations

The walls and ceiling (not just the insulation) of the futuristic Xanadu House were built out of polyurethane foam. Domed ceilings and other odd shapes are easier to make with foam than with wood. Foam was used to build oddly-shaped buildings, statues, and decorations in the Seuss Landing section of the Islands of Adventure theme park. Speciality rigid foam manufactures sell foam that replace wood in carved sign and 3D topography industries. PU foam is also used as a thermal insulator in many houses.

Polyurethane resin is used as an aesthetic floor solution. Being seamless and water resistant, it is gaining interest for use in (modern) interiors, especially in Western Europe.

Polyurethane being used as an insulator in house construction.

Polyurethane used as a flooring solution.

Being poured as a liquid after which it hardens out, polyurethane is a floor solution that can be applied seamlessly.

 

Construction sealants and firestopping

Head-of-Wall Firestop Joint: the presence of penetrants demonstrates the need to have both operational and fire-tested compatibility between the joint sealant and mechanical/electrical through-penetrations. In other words, it is easier to insist on the use of joint firestops that can also be used for penetration seals, as otherwise penetrants may be run by mechanical and electrical subtrades that unintentionally void the fire-resistance rating of the wall, which jeopardises the entire fire safety plan in place for a building.
Head-of-Wall Firestop Joint penetrated by both electrical and mechanical services, demonstrating the need for operational and fire-tested compatibility between the joint firestop system and penetrants, be they electrical, mechanical or structural.

Polyurethane sealants are available in 1, 2 and even 3 part systems, either in cartridge, bucket or drum format. Polyurethane sealants are also sold for firestopping applications. Obviously, the sealant by itself provides no serious hindrance to fire, as its hydrocarbon bonds readily support combustion. However, when backed by inorganic insulation, such as rockwool or ceramic fibres, it can act as an effective seal to thwart smoke and hose-stream passage, particularly in inorganic joints. It is, however, advisable to avoid direct contact with metallic penetrants and through-penetrating cables, as the heat carried by the penetrants may jeopardise the sealant. This, however, requires a lot of vigilance. In concrete to concrete, or concrete to masonry joints, however, that are free of mechanical or electrical penetrants, it works well and dependably.

 

Surfboards

Some surfboards are made with a solid polyurethane core. A rigid foam blank is molded, shaped to specification, then covered with fiberglass cloth and polyester resin.

 

Rigid-hulled boats

The hull of the Boston Whaler motorboat is polyurethane foam sandwiched in a fiberglass skin. The foam provides strength, buoyancy, and sound deadening.

 

Inflatable boats

Some raft manufacturers use urethane for the construction ofinflatableboats. AIRE uses urethane membrane material as an air-retentive bladder inside a PVC shell, whereas SOTAR uses urethane membrane materials as a coating on some boats. Maravia uses a liquid urethane material which is spray-coated over PVC to enhance air retention and increase abrasion resistance.

 

Tennis grips

Polyurethane has been used to make several Tennis Overgrips such as Yonex Supergrap, Wilson Pro Overgrip and many other grips. These grips are highly stretchable to ensure the grip wraps neatly around the racquet's handle.

 

Electronic components

Often electronic components are protected from environmental influence and mechanical shock by enclosing them in polyurethane. Typically polyurethanes are selected for the excellent abrasion resistances, good electrical properties, excellent adhesion, impact strength,and low temperature flexibility. The disadvantage of polyurethanes is the limited upper service temperature (typically 250 °F (121 °C)). In production the electronic manufacture would purchase a two part urethane (resin and catalyst) that would be mixed and poured onto the circuit assembly (see Resin casting). In most cases, the final circuit board assembly would be unrepairable after the urethane has cured. Because of its physical properties and low cost, polyurethane encapsulation (potting) is a popular option in the automotive manufacturing sector for automotive circuits and sensors.

 

Adhesives

Polyurethane is used as an adhesive, especially as a woodworking glue. Its main advantage over more traditional wood glues is its water resistance. It was introduced in the general North American market in the 1990s as Gorilla Glue and Excel, but has been used much longer in Europe.

On the way to a new and better glue for bookbinders, a new adhesive system was introduced for the first time in 1985. The base for this system is polyether or polyester, whereas polyurethane (PUR) is used as prepolymer. Its special feature is the coagulation at room temperature and the reacting to moisture.

First generation (1988 at the drupa)

  • Low starting solidity
  • High viscosity
  • Cure time of more than 3 days

Second generation (1996 at the drupa)

  • Low starting solidity
  • High viscosity
  • Cure time of less than 3 days

Third generation (2000 at the drupa)

  • Good starting solidity
  • Low viscosity
  • Cure time between 6 and 16 hours

Fourth generation (present)

  • Good starting solidity
  • Very low viscosity
  • Cure reached within a few seconds due to dual-core systems

Advantages of polyurethane glue in the bookbinding industry:

  • PUR is real wonder compared to hotmelt and cold glue. Because of the missing moisture in the glue, papers with wrong grain direction can be processed without problems. Even printed and supercalandered paper can be bound without problems. It is the most economical glue with an application thickness of theoretical 0.01 mm. But in reality it is not possible to apply less than 0.03 mm.
  • PUR glue is very weather-proof and stable at temperatures from -40 °C to 100 °C.citation needed

 

Watch-band wrapping

Polyurethane is used as a black wrapping for timepiece bracelets over the main material which is generally stainless steel. It is used for comfort, style, and durability.

 

Abrasion resistance

Thermoset polyurethanes are also used as a protective coating against abrasion. Cast polyurethane over materials such as steel will absorb particle impact more efficiently. Polyurethanes have been proven to last in excess of 25 years in abrasive environments where non-coated steel would erode in less than 8 years. Polyurethanes are used in industries such as:

  • Mining and mineral processing
  • Aggregate
  • Transportation
  • Concrete
  • Paper processing
  • Power
  • Inflatable boat manufacture

 

Filling of spaces and cavities

Two Binary liquids, one of which is a polyurethane (either T6 or 16), when mixed and aerated, expand into a hard, space-filling aerosolid.

 

Textiles

A thin film of polyurethane is added to a polyester weave to create polyurethane laminate (PUL), which is used for its waterproof and windproof properties in outerwear, diapers, shower curtains, and so forth.

 

Testing

 

Effects of visible light

Polyurethanes, especially those made using aromatic isocyanates, contain chromophores which interact with light. This is of particular interest in the area of polyurethane coatings, where light stability is a critical factor and is the main reason that aliphatic isocyanates are used in making polyurethane coatings. When PU foam, which is made using aromatic isocyanates, is exposed to visible light it discolors, turning from off-white to yellow to reddish brown. It has been generally accepted that apart from yellowing, visible light has little effect on foam properties.29 30 This is especially the case if the yellowing happens on the outer portions of a large foam, as the deterioration of properties in the outer portion has little effect on the overall bulk properties of the foam itself.

It has been reported that exposure to visible light can affect the variability of some physical property test results.31 Increasing exposure time and/or light intensity during the storage of foam samples under ambient laboratory conditions increased the amount of permanent set induced in some compression set tests (the samples did not fully return to their original size and/or shape). Variability resulted from uncontrolled light exposure of cut samples prior to being compressed. Other foam properties were not substantively affected. It was recommended that specimen preparation and testing be done rapidly to minimize variation in results or if specimens are prepared but not tested for a week or more, that the samples should be protected from light exposure.

Higher-energy UV radiation promotes chemical reactions in foam, some of which are detrimental to the foam structure.

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