Properties of polyurethane foam with fourth-generation blowing agent

Climate change makes it imperative to use materials with minimum global warming potential. The fourth-generation blowing agent HCFO-1233zd-E is one of them. The use of HCFO allows the production of polyurethane foam with low thermal conductivity. Thermal conductivity, like other foam properties, depends not only on the density but also on the cellular structure of the foam. The cellular structure, in turn, depends on the technological parameters of foam production. A comparison of pouring and spray foams of the same low density has shown that the cellular structure of spray foam consists of cells with much less sizes than pouring foam. Due to the small size of cells, spray foam has a lower radiative constituent in the foam conductivity and, as a result, a lower overall thermal conductivity than pouring foam. The water absorption of spray foam, due to the fine cellular structure, also is lower than that of pouring foam. Pouring foam with bigger cells has higher compressive strength and modulus of elasticity in the foam rise direction. On the contrary, spray foam with a fine cellular structure has higher strength and modulus in the perpendicular direction. The effect of foam aging on thermal conductivity was also studied.

Failure strength predictions for closed-cell polyvinyl chloride foams

This paper describes an effort to model mechanical strength of closed-cell polyvinyl chloride foams under static loading. The study presented here is a continuation of an earlier study to model elastic stiffness of closed-cell polyvinyl chloride foams as effective transversely isotropic materials. An engineering approach is used in the study and governing equations are developed for predicting the strength of polyvinyl chloride foams. To account for foam microstructure and cell-shape anisotropy on foam strength, a unit cell representation of the polyvinyl chloride foam microstructure is used to derive equations to assess tensile and shear strengths of polyvinyl chloride foams. The differential stretching of polyvinyl chloride foam cell walls (in the rise direction and in the in-plane directions) on the strength of the foam-matrix polymer is also taken into account in modeling the mechanical strength of polyvinyl chloride closed-cell foams. The behavior of closed-cell polyvinyl chloride foams under compression is different from that under tension. In the paper, the equations for predicting compressive strength of closed-cell polyvinyl chloride foams are based on an approximate theory developed in an earlier study of compressive strength of unidirectional composites. The validity of the foam strength predictive equations, derived in the paper, is first demonstrated through comparison of the predictions with the results on Divinycell H (DIAB) foams obtained from a systematic in-house test program. A comparison is also carried out between the strength predictions and the test results published by two polyvinyl chloride foam manufacturers for different density polyvinyl chloride foams. Good agreements are found for all the different density foams studied.

Energy - Absorption and Efficiency Diagrams of Rigid PUR Foams

Polyurethane (PUR) foam materials represent a class of materials widely used for impact protection and energy absorption. This paper presents a characterization of different rigid PUR foams under compressive impact loading by means of energy absorption and efficiency diagrams. Compressive properties were investigated on cubic specimens on the foams’ rise direction at room temperature with a loading rate of 3.09 m/s for three different closed-cell foams with densities of 100 kg/m3, 160 kg/m3 and 300 kg/m3 respectively. Experimental results show that the compression modulus, yield stress and plateau stress increase with density. Most of the energy is absorbed in the plateau region because of the cell deformation associated with this phenomenon, allowing greater absorption of impact energy at nearly constant load. Authors have found that both the energy absorption and efficiency diagrams are consistent and present similar results for studied foams.

Fracture Toughness of PIR Foams Produced from Renewable Resources

Rigid low-density closed-cell polyisocyanurate (PIR) foams are used primarily as a thermal insulation material. Traditionally, they are manufactured from constituents produced by petrochemical industry. Introducing renewable materials in PIR formulation brings definite economical and environmental benefits. Fracture toughness of PIR foams obtained from renewable resources (with the polyol system comprising up to 80% of rapeseed oil esters) and petrochemical PIR foams has been characterized experimentally, by compact tension tests, for mode I crack propagation along the rise direction of the foams.

Experiments on Elastic Polyether Polyurethane Foams Under Multiaxial Loading: Mechanical Response and Strain Fields

We study experimentally the mechanical response of elastic polyether polyurethane (EPP) foams up to large strains over the range of commercially available densities and for a variety of loading conditions. To this end, we subject the foams in a set of EPP foams to five different tests, namely, compression along the rise direction, compression along a transverse direction, tension along the rise direction, simple shear combined with compression along the rise direction, and hydrostatic pressure combined with compression along the rise direction. The set of EPP foams consists of foams of five apparent densities ranging from 50.3 kg/m3 to 221 kg/m3. For each test and foam density, we report the mechanical response in the form of a stress-strain curve or a force-displacement curve. For some tests and foam densities, we use a digital image correlation method to measure the strain field on the surface of the foam. In a discussion of our experimental results, we put emphasis on the relation between the stress-strain or force-displacement curve recorded in a test and the attendant strain fields.

Development and Characterization of Novel Interpenetrating Network (IPN) Foams from Epoxy Ester and Aliphatic Epoxy Resin

Diglycidyl ether of bisphenol-A (DGEBA) was reacted with acrylate monomer at variable molar ratios. The reaction between glycerine and epichlorohydrine form glycidyl ether of polyol aliphatic epoxy resin. The resultant resins were characterized duly. Both the resins were mixed at different ratios with constant high shear stirring. The obtained mixture and suitable additives were heated at 150oC for one and half hour. The so called Interpenetrating Network (IPN) transformed into foams. The performance of foams was evaluated by testing for compression in both parallel and perpendicular to rise direction. The tests were carried out at room temperature and at the elevated temperature. The compression properties showed a decreasing trend for increasing amounts of glycerine resin. The density and thermal properties of epoxy foams were also evaluated. The relation between the composition, density and properties of the foam was analyzed.