Cellular Polymers

Polyurethane-polyisocyanurate rigid (PIR) foams are used as thermal insulation materials in a wide range of applications such as construction and pipe insulation. Some of the utilizations require the maximum operating temperature of these materials to reach extremely high temperatures. This work is devoted to the study of changes in the chemical composition and the main physical-mechanical and thermophysical characteristics of PIR foams subjected to prolonged extreme heating in the presence of the material direct contact with air and in its absence. Based on the results obtained, prolonged extreme heating of such materials leads to a significant change in their chemical composition, mainly due to the thermal decomposition of allophanate, urethane and urea linkages, as well as the gradual formation of uretidione, linear carbodiimide polymer and the oxidation of ethers to esters. The relative compressive strength of these materials changes only to a small extent, while the thermal conductivity of these materials increases significantly during heating.

Silica aerogel (SA) was functionalized by γ-amino propyl triethoxy silane (APTES) with long chain amino groups, and this surface-functional SA was filled into rigid polyurethane (PU) foams to enhanced mechanical property and thermal insulation. It was proved that the active functional groups and different content of SA (0.3, 0.5, 0.7 and 0.9 wt%) played important roles in controlling cellular structure of PU foams. The results of the scanning electron microscopy (SEM) and water absorption showed that the surface-functionalized SA made the cell uniformly and reduced the number of damage cells. The surface-functionalized SA had a positive effect on the hardness and density of the foams. Moreover, the thermal conductivity of PU foams was reduced by 17.60% and the compressive strength was increased by 43.27% at 0.5 wt% filler of surface-functional SA. The active functional groups (amino groups) of surface-functional SA could take place PU foaming reaction and enhance the interactions and compatibility between SA and matrix. Thus, these foams with small amounts of filler would find vast applications in the thermal insulation sectors.

In this study, montmorillonite (MMT) clay was utilized as solid particle contributing to stabilize high internal phase emulsions (HIPEs) for the production of polyHIPE foam composites. Cetyltrimethylammonium bromide (CTAB) immobilization onto the MMT surface was carried out using cryoscopic expansion (C-XP) and physical adsorption in solution (SOL) techniques. A series of experiments were conducted to determine the amounts of clay and surfactant that provide the stability of HIPE. In addition, the morphologies, surface areas, dye adsorption capacities and glass transition temperatures together with heat capacity differences of the PolyHIPE materials were investigated in terms of nanoclay modification techniques and surfactant and MMT clay amounts. It was found that minimum 5% (vol.) of surfactant was needed to maintain the stability of neat HIPE whereas the surfactant requirement to ensure emulsion stability decreased to 1 vol in presence of the clays in quite low amounts (0.25 to 1.00 wt%). In all composites, polyHIPE morphology was preserved, predominantly resulting in open-cell structures. In fixed amounts of both clays, decreasing surfactant concentration reduced homogeneity of pore size distribution and caused pores in different sizes. An opposite effect was observed with increasing clay content at a fixed surfactant concentration, leading to a reduction in pore sizes and homogenization of pore size distribution. The cationic dye (Nile Blue) adsorption capacity of the composites was evaluated and the highest adsorption capacity among them was exhibited by the composite containing 0.75% CTAB-XP-MMT, which adsorbed 589% more dye compared to neat polyHIPE foam. Moreover, helping to ensure the emulsion stability of the clays, they also benefit in terms of taking an active role in the adsorption of the dye from water.

To reduce the dependency of human life and industrial materials on petroleum, developing renewable and environmentally friendly materials has become one of the research hotspots. In this paper, Soy-DGP was synthesized through a ring-opening reaction between epoxy soybean oil (ESO) and diethylene glycol (DG), followed by a reaction with phenylphosphonyl dichloride(PPDC). Flame-retardant polyurethane foam (RPUF-DGP) was then produced by reacting various amounts of Soy-DGP with isocyanate (p-MDI). It was observed that the addition of Soy-DGP led to a reduction in the mechanical properties due to a decrease in the apparent density of RPUF-DGP. Microscopically, as Soy-DGP was added, the bubble pore size did not change significantly, but the uniformity of the aperture size was decreased. Additionally, the limiting oxygen index (LOI) of RPUF-DGP improved from 19.2% to 22.6% upon adding 80 wt% Soy-DGP. Both the time to ignition (TTI) and time to peak heat release rate (TTP) for RPUF-DGP decreased with increasing Soy-DGP content, shortening the continuous burning time of samples. Examination of the residual carbon structure showed that higher quantities of Soy-DGP resulted in thicker carbon layers on the surface of RPUF-DGP, along with bead-like phosphoric acid formation within the system, which delayed degradation.

Foamed materials are used in many everyday objects, including hot and cold beverage cups. In this research study, the compression behaviour of foamed polypropylene sheet samples used for thermoformed cups is investigated using finite element simulations. Computed tomography (CT) is utilised to examine the microstructure of two extrusion foam sheet samples prior to thermoforming. The samples consist of highly non-uniform cells. Therefore, finite element meshes are created directly from the CT measurements to reproduce the microstructure in detail. The meshes can be used for the mechanical characterisation. In order to validate the simulation models, experimental tensile tests are carried out, as compressive tests are not possible experimentally due to the small thickness of the samples. The validation shows that the tension behaviour in extrusion direction can be well depicted by the microstructural models. One validated model is then used to evaluate the compression behaviour at different stretching degrees to replicate the mechanical behaviour after the thermoforming process. The results show that the stretching of the foam highly affects the compression properties, so the higher the stretching, the lower the compressive strength.