Historical Developments In Polyurethane Foam Biology Essay

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Polyurethanes were studied first by Otto Bayer and his co-workers in Germany. Independently polyurethanes were studied by T. Hoshino and Y. Iwakura in Tokyo Institute of Technology in Japan. And also a research group started research in polyurethanes at DuPont de Nemours co. in United States. In case of foams the first invention in class of iso-cyanate foam is polyamide foam not polyurethane foam. Polyamide foam was formed by two step process in which first step was preparation of carboxyl terminated polyester oligomer and second step was the reaction of oligomer with isocyanate component. This method was invented in 1941.

First patent of flexible urethane foam came in 1942. It contains many reactions in one step process. TDI was used and polyurethane chains were formed by reaction of isocyanate group with hydroxyl group. Carbon dioxide was produced by the reaction of di-isocyanate with water. The reaction was highly exothermic.

Another important development was of polyether polyol before it polyester polyols are used but after appearance of polyether polyol it became major reactant of flexible foam. Development of silicone surfactant and silicone co-polymer which can be used as a surfactant is also important innovation in flexible urethane foams because use of silicone surfactant promotes foaming stability and if it is used in rigid foams it increases insulation properties of foam.

The debut of physical blowing agent CFC 11 also opened a new innovative approach in the field of urethane foams but due to some environmental considerations after some time it was banned to use in foaming systems. Then to tackle this problem research was being carried out which lead to the appearance of third generation blowing agents and these third generation blowing agents include C5 hydrocarbons, Halogen free azeotopes, liquefied carbon dioxide and water. Now a days water is used mostly as a blowing agent. Urethane foams both flexible and rigid can cause serious fire hazards and this problem highlited the importance of flame retardants in foaming processes. [2,3]

Research is still going on to improve the production and performance characteristics of the product and so far many different types of polols, catalysts, blowing agents and other chemicals are known which provide better foaming product with better characteristics than the previous ones. But still research is going on to improve the foaming products used commercially.

3.2 Production of polyurethanes by enzymes

Shuichi Matsumura, Yasuyuki Soeda, and Kazunobu Toshima worked on new perspective for synthesis of polyurethanes. As polyurethanes are produced by using polyols and toxic di-isocyanates which are produced from more toxic phosgene and due to this reason polyurethane produced is resistant to biodegradation. Enzyme-catalyzed polymerization and degradation is introduced by these researchers for synthesis of environmentally sustainable polyurethane. This is the new idea for production of polyurethane without using diisocyanate, the biodegradation of polyurethane, and the enzymatic synthesis and the chemical recycling of poly(ester-urethane) (PEU) and poly (carbonate-urethane) (PCU). The catalyzed polymerization of low molecular weight and biodegradable urethane diols with short-chain dialkyl carbonate and alkanedioates produced PCU and PEU, respectively. They were readily degraded in an organic solvent into the repolymerizable cyclic oligomers. These results will be applicable for the production strategies of green and sustainable polyurethanes. [4]

3.3 Castor Oil based polyurethanes

The use of renewable resources for synthesis of polyurethane is of larger interest. Muneera Begum and Siddaramaiah investigated that how castor oil is used to produce polyurethanes. Castor oil contains both unsaturated and conjugated hydroxyl groups. Castor oil reacts with di-isocyanates to form a pre-polymer which is pre-polyurethane. Pre-polyurethanes are linear block co-polymers. Poly Butyl methacrelate PBMA is also produced in this process. Chemicals used are TDI 80/20, Di butyl tin dilurate DBTA as catalyst and ethylene glycol as cross linker. [5]

3.4 Polyurethane foams with cellulose derivatives

J.L. Rivera-Armenta investigated about the new polyurethane foams prepared by using cellulose derivatives as raw materials by one shot process. Polyurethanes being used in agricultural and medicinal applications are discarded after being used and this causes a contamination due to difficulty in their disintegration and effect environment adversely. To solve this problem scientist proposed that cellulose derivatives can be used as raw materials in foam synthesis and cellulose derivatives used are carboxy methyl cellulose, cellulose sulphate, cellulose acetate and tri methysilyl cellulose. The use of these natural materials adds into the bio-degradation to flexible foams. [6]

3.5 Glycol influence on flexible foams

Carolina Molero and co-workers studied glycol influence on flexible foams in process of recovering polyol from foam by its re-cycling. Scrap of flexible polyurethane foams from slabstock manufacturing comprises about 10% of the total production, leading to not only an environmental problem but also an economic one. The general purpose of polyurethane chemical recycling is to recover a valuable constituent, the polyol. Research by scientist shows that glycolysis is best for recovering polyol. Glycolysis of flexible polyurethane foams in ''split phase'' was conducted with different glycols. Diethylene glycol is suitable glycol to obtain a high purity in the polyol phase. [7]

3.6 Polyurethane foam with semi fluorinated surfactants

Maarten J. Krupers, Camiel F. Bartelink and co-workers studied that rigid polyurethane foam is prepared when semi fluorinated di-block co-polymer is employed as a surfactant. These flourosurfactants include block of polymethyl meth acrelate PMMA which includes per flouro alkyl groups which are either hexyl or butyl. Sample of foams were also prepared using commercially available silicone surfactant and it is noted that foam samples in which fluorinated surfactant is used contain many small cells and finer surface than other samples. [8]

3.7 Polyurethane foams from micro-emulsions

Christian Ligoure studied the relationship between the degree of expansion of polyurethane foams and structure of premix. Polyurethane foams obtained from reacting premixes containing micro-emulsions are highly expanded. The expansion rate is proportional to the volume fraction of micro-emulsion in the premix. The stability of premixes with and without micro-emulsions is completely different showing distinct creaming mechanisms. Polyurethane foams are synthesized successfully from micro-emulsions and this idea can be applied to industrial foaming processes where large expansions are required. [9]

3.8 TDI based polyurethane foam

Mark F.Sonnenschein and Robbyn Prange studied about synthesis of polyurethane foam using TDI. Their work showed that TDI based polyurethane foams are prepared by taking polyol, surfactant, catalyst and water as a separate stream and it was stirred for 30 minutes at about 600 rpm. Then this mixture is transferred to polyol tank where it is circulated for more 30 minutes so that this mixture reaches thermal equilibrium. Then the polyol stream is mixed with TDI stream at very fast rate and foam is produced. Slab-stock foaming procedure is used in it. [10]

3.9 Orthogonal cutting of foam

Sharif F.F Malik introduced a new method in cutting of foam after its production this is orthogonal cutting. Orthogonal cutting experiments are performed on rigid polyurethane foams of various densities and cell sizes, to investigate chip formation and surface finish. An optical arrangement was used to visually record the cutting process, while horizontal and vertical cutting forces were measured. A total of 239 measurements were performed with tool rake angles of 23; 45 and 60; and depths of cut in the range of 0.1-3 mm. Continuous and various modes of discontinuous chip formation were identified. While continuous chip formation resulted in smooth surfaces, discontinuous chip formation was often associated with surface damage in the form of crate ring as a result of crack propagation. [11]

3.10 Structure-property relationship of foams

Garth L.Wilkes studied the relationship between structure and properties of flexible foam. Visco-elastic and compression set properties of flexible foams are studied as a function of temperature and humidity for different moulded foams based on TDI and glycerol and results are compared with the products of conventional slab-stock machine process having same TDI and glycerol. It was found that high temperature and humidity plasticizes the foams. [12]

3.11 Thermal Characteristics of polyurethane foams

Nihal Sarier studied thermal characteristics of polyurethane rigid foams that have been widely used for thermal insulation. Through a laboratory-scale work, two paraffin waxes acting as phase change materials, namely n-hexadecane and n-octadecane, each of which is capable of managing large heat storage/release, were directly incorporated into the polyurethane foams at different ratios. Polymerization modified by means of n-alkane addition could be achieved without any adverse effect. Results show that polyurethane foams can be designed as thermal insulators equipped with an improved buffering function against temperature changes. [13]

3.12 Bubble growth in two dimensional Visco-elastic foam

H.J Wilson and his co-workers studied bubble growth in visco-elastic foam. The effects of visco-elasticity on the expansion of gas bubbles arranged in a hexagonal array in a polymeric fluid are investigated. The expansion is driven by the diffusion of a soluble gas from the liquid phase, and the rate of expansion is controlled by a combination of gas diffusion, fluid rheology and surface tension. In the diffusion limited case, the initial growth rate is slow due to small surface area, whereas at high diffusivity initial growth is rapid and resisted only by background solvent viscosity. Beyond this time the bubble expansion is controlled by the relaxation of the polymer. It is also investigated that how visco-elasticity effect the shape of bubble in foaming systems. [14]

3.13 Fracture toughness of polyurethane foam

Liviu Marsavina, Tomasz Sadowski are first to study the fracture toughness of flexible foams. Effect of impregnation on fracture toughness is studied. Two resins i-e epoxy resin and polyester resins are used to impregnate foam samples to increase their durability. Impact tests are performed using notched specimens and the results show that impregnation increases fracture toughness by 27%. [15]

3.14 Visco-elastic properties of flexible foams

R.Singh, P. Davies, and A.K Bajaj studied Visco-elastic properties of flexible urethane foams by various mechanisms and then properties are reported and results are compared with the test results of flexible foam samples and it is found that flexible foam can also exhibit both viscous and elastic behavior under some conditions. [16]

3.15 Bio degradability of polyurethane foam

Meltem Urgun Demirtas studied the integrity of PU foam using short-term accelerated laboratory experiments including bioavailability assays, soil burial experiments, and accelerated bioreactors to determine the fate of PU foam in the soil where anaerobic processes are dominant. The experimental results have shown that the studied PU foam is likely not biodegradable under anaerobic conditions. Neither weight loss nor a change in the tensile strength of the PU material after biological exposure was observed. [17]

3.16 Thermal Expansion of polyurethane foam

Kit-Lun Yick and Long Wu studied and developed a model to study thermal expansion of polyurethane foam and its effects on the structure of foaming product experiments are performed by taking samples of flexible foam and its thermal behavior is studied. [18]

3.17 Visco-elastic foam

Richard S. Schmidt investigated about visco-elastic foam along with other scientists and showed that visco-elastic foam was commercialized by NASA and first used by NASA in space shuttle seats to provide comfort to astronauts. [20, 21, 22] It is used in large number of applications and now it has become major mattress industry of the world. Teodor Socaciu and Mihai Simon studied applications of VE foam in shoe industry and also research are carried on to improve the product. Visco-elastic foam is expensive foam and research is underway to make it cost effective. [21]

3.18 Flexible foams with soybean polyol

According to new research by Ling Zhang and Hyun K.Jeon polyether polyol is now replaced in flexible foams and flexible foams can be synthesized using soybean polyol with Styrene acrylo nitrile co-polymer poyol. Increase in compression modulus is observed for this foam as compared to the foam produced by polyether polyol. [23]

3.19 Flexible foams with palm oil polyol

Ryohei Tanaka, Shigeo Hirose and Hyoe Hatakeyama studied another latest advancementin urethane foams which is the use of palm oil polyol in flexible urethane foams, in this process first palm oil polyol is converted to mono glycerides by glycerolisis and then foam is prepared by mixing polyol with polyethylene glycol PEG or di-ethylene glycol DEG which is used as isocyanate compound. This is the latest development in flexible foams. [24]

3.19 Rigid foam by soybean polyol and sugar cane bagasse polyol

Suqin Tan, Tim Abraham and Don Ference carried out research on use of soybean polyol for production of rigid polyurethane foam. [25]

3.20 Rigid foam by sugar cane bagasse polyol

A.A Abdel Hakim, Mona Nassar, Aisha Emam and Maha Sultan synthesized rigid polyurethane foam using a bio-polyol which is prepared from sugar cane bagasse with MDI. Results are better than the other reactants used for rigid foam. This is the latest development in rigid polyurethane foam. [26]