Showing papers in "Cellular Polymers in 1994"

MDI comfort cushioning for automotive applications

Abstract: This paper seeks to investigate the dynamic aspects of seat comfort which are known to be strongly influenced by the intrinsic properties of the flexible foam used. Within this framework, a comparative analysis of the dynamic comfort performance of conventional seating foam and ICI's new comfort foam technology is presented

Relating the properties of foam to the properties of the solid from which it is made

Abstract: Properties of foam and the solid (neat resin) from which it was derived were compared experimentally for polymethacrylimide (PMI). Viscoelastic properties of the foam and neat resin differed significantly in the range 50 Hz to 5 kHz. No significant differences in thermal properties were observed in differential scanning calorimetry. However, it was observed that the stiffness of the solid material from which the foam was made was increased after heat treatments. It is therefore likely that the properties of the solid material in the foam are changed by the foaming process, which involves elevated temperature. The properties of the solid material in the foam were also inferred from the measured foam properties substituted into the given foam structure-property relations

Inherently flame retardant rigid polyurethane foams based on new triazinic polyether polyols

Abstract: The synthesis of new triazinic polyols by oxyalkylation with the propyleneoxide of some well known condensation products derived from melamine (2,4,6triamino-1,3,5-triazine), a heteroaromatic chain initiator, has been studied. By using the synthesized aromatic triazinic polyols in conventional foaming processes, rigid polyurethane foams with excellent physico-mechanical properties and inherent flame retardancy are obtained, better than those of rigid polyurethane foams derived from conventional aliphatic polyols based on sucrose. A new additive flame retardant with a similar heteroaromatic triazinic structure (1,3,5-trichlormethylisocyanurate) was also successfully evaluated. The non expensive and accessible raw materials, the facility of the reactions involved in this kind of synthesis, make the studied method very attractive from technological points of view

Development of crosslinked flexible PVC foam formulations

Abstract: Experiments were carried out to develop a peroxide based plasticised PVC formulation from which a crosslinked foam could be produced. Thermal analysis was used to investigate the reactions which occurred during crosslinking and blowing, and to select a suitable peroxide and crosslinking temperature. Solvent extraction was used to assess the amount of crosslinked material (gel content), and thermomechanical analysis was used to measure softening temperature of the foams produced. For selected samples, the reaction was scaled up so that tensile properties could be measured. Providing that a suitable peroxide was well dispersed in the plastisol, and in the presence of a crosslinking monomer, uniform crosslinked foams could be produced when a suitable spreading temperature was used

Experimental study of size effects and surface damage in closed-cell polymethacrylimide and open-cell copper foams

Abstract: This article describes experimental investigations of size effects in torsion and bending of lathe cut closed-cell polymethacrylimide and open cell copper foams. Slender specimens were found to have a slightly smaller effective stiffness than thick ones. This behaviour is consistent with a model of surface damage to the outermost cells of the foam. The surface damage layer was inferred to be from 0.13 to 0.37 cell diameters for the polymethacrylimide, depending on the grade of foam, and from 0.3 to O.4 cells in the copper foam. Effects of Cosserat (micropolar) elasticity, which would give rise to an effective stiffening of slender specimens, were not observed

Latest manufacturing solutions for slabstock foams

Abstract: As environmental pressure increases worldwide, it is becoming necessary for foamers to eliminate chlorinated products - such as chloro fluoro carbons (CFCs), methylene chloride, 1.1.1 trichloroethane - or any type of volatile organic compounds (VOC's) from their production. In some countries these additives have already been banned: the impact on the flexible foam industries would be to increase foam prices and to eliminate certain soft grades. The use of liquid carbon dioxide (CO 2 ) as an expanding agent in a polyurethane foam is a good and well accepted idea. Handling this liquid, which gasses off at room temperature, has always been one of the main problems

Graft polyether polyols based on α-methylstyrene and acrylonitrile for flexible polyurethane foams

Abstract: The radical grafting copolymerisation reaction of α-Methylstyrene (α-MeSt) and Acrylonitrile (AN) as compared with the usual grafting copolymerisation reaction of Styrene (St) and AN on the polyetheric chains of polyether polyols for polyurethanes, homopolymers of propyleneoxide (PO) or copolymers PO-ethyleneoxide (EO), has been studied. The effect of St substitution by α-MeSt, another cheap and accessible vinylic monomer, has been investigated, concerning the properties of the resultant graft polyethers and the physico-mechanical properties of the resultant flexible polyurethane foams. Special attention was paid to the solid fractions isolated from the polymer polyols proving that the the synthesized products are true graft copolymers and not a physical mixture between vinyl copolymers and polyether polyols

Friction and the dynamic mechanical and thermal properties of polyurethane elastomers. II: Microcellular polyurethanes

Abstract: The results reported indicate that the properties of polyurethanes elastomers can be tailored to serve a wide variety of applications, for low temperature uses as well. The glass transition temperatures of the soft segments (T gs ) which control the low temperature properties of polyurethane elastomers, ranged from -79°C to -27°C (DSC onset values). The transitions observed in the range 75 to 125°C were attributed to hard segment glass transitions. The transitions at temperatures from 140 to 170°C, which were identified especially in the samples of over stoichiometric diisocyanate concentration, evidently arose from the dissociation of allophanate crosslinks and successive ordering processes. The low temperature β and γ transitions were observed at temperatures from -70°C to -125°C. In addition to the obvious Schatzki crankshaft mechanism, allophanate crosslinking may influence these transitions. Samples that were annealed over the crystal melting temperature and subsequently quenched exhibited higher glass transition temperatures than the samples kept for a long time at room temperature. These results can be explained in terms of better phase separation in annealing and formation of small soft segment crystallites in quenching, in contrast to the formation of large crystalline and amorphous phases in the RT samples

CFC-free rigid polyurethane foam insulation products

Abstract: This paper provides an overview of the commercially successful CFC-free rigid polyurethane insulating products now established in the UK market, which have been made available because of the need to move away from the use of potent ozone depleting CFC blowing agents used for the past 35 years. Detailed evidence is included to support the claim that the performance of these new products and their life expectancy is equal to that of their CFC based counterparts. It shows that because of the great diversity of products and applications, that currently five different blowing agents are used since whilst many ozone benign blowing agents exist, none matches the other unique features of the CFCs R11 and R12 entirely. Nevertheless it is demonstrated that the products now in use in the UK, by comparison with their CFC counterparts, are playing a significant part in eliminating the threat to the ozone layer, whilst at the same time being able to continue to make their significant contribution to the reduction of CO 2 emissions, believed to be the main cause of global warming

The Use of Pentanes As Blowing Agent in Rigid Polyurethane Foam for Lamination

Abstract: Pentanes tend to be considered as long-term alternative blowing agents for rigid polyurethane foams. They are environmentally friendly, non-toxic and economically feasible. A major drawback of the use of pentanes is their flammability and their relatively high thermal conductivity, compared to CFC-11. As pentane processing techniques have improved considerably, safety can now be insured at a reasonable price. In this paper the overall performance of pentane blow laminates in terms of processing, insulation value, mechanical properties and flammability is demonstrated. The ageing characteristics are compared to those of CFC-11 blown foams. The low vapour pressure of both n-pentane and cyclopentane is shown to induce condensation effects. The consequences of condensation in terms of thermal conductivity and dimensional stability are discussed. The problem of pentane solubility in the polymer matrix and its influence on the long-term foam performance is addressed. Possible solutions are presented.