Showing papers in "Cellular Polymers in 2023"

Role of hemp fiber addition on thermal stability, heat insulation, air permeability and cellular structural features of rigid polyurethane foam

Abstract: In this current study, rigid polyurethane foams (RPUFs) composites were prepared using different percentage (3, 6, 9 and 12%) of the hemp fibers via one-shut one-step polymerization method. The influences of the hemp fiber addition on the RPUFs were investigated meticulously by means of Fourier-transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), thermal conductivity measurement and scanning electron microscopy (SEM) techniques by evaluating the alternations in the chemical structures of the component, thermal stability, apparent density, insulation performance and cellular topology of the produced samples. The structural analysis revealed that there existed the strong secondary chemical bonds between the functional groups belonging to the components and, depending on that, the improvement in the thermal stability of the foam samples was recorded accompanied by the formation of the better interfacial adhesion. Furthermore, thermal conductivity values of the hemp fiber-loaded RPUFs were observed to increase regularly with the increasing of the content level of the hemp fibers. This was explained by enhancement in the bulk phase conduction level depending of the apparent density rising, reduction in CO2 concentration inside cells as well as the formation of the distorted cellular structures. The obtained air permeability results displayed that the hemp fibers incorporated successfully with RPUF structure, which provides the occurrence of the novel micro barriers and pathways limiting the passage of the air throughout the matrix. The taken scanning electron microscopy images also indicated that the cellular morphology and dimensional stability of the produced foams affected negatively by the hemp fiber addition. At high contents, the wrinkled, non-uniform and irregular cellular structures were observed with ruptured and collapsed walls and struts.

Influence of particle geometry and size on the cell morphology of vacuum assisted rotationally molded foam

Abstract: An increased awareness of sustainability among the population leads, from an industrial point of view, to efforts to act more ecologically as well as to the aim for lower production costs and an increased efficiency. With this in mind, a new process has been developed for foaming without blowing agents in rotational molding. Process related air inclusions in the polymer melt are expanded to form the cell structure by means of vacuum application. In the presented study, the influence of different particle sizes as well as the arising potential of deploying microgranules in the otherwise powder-based process is investigated with regard to the resulting foam cells. The results confirm that particle size and form greatly influence the existence and size of air inclusions in the polymer melt. It could be proven that these differences, caused by the particle characteristics, propagate during the foaming process and lead to different cell morphologies in the resultant foam. Furthermore, it is indicated that qualitative predictions of the resulting cell dimensions can be made on the basis of bulk density measurements and the analysis of the sintering behaviour of the initial particles.

A study of the cell morphology and mechanical properties of bumper material PP-T-EPDM composite foam

Abstract: In this study, cellular polypropylene based composite foams were prepared using an universal injection moulding machine. The chemical foaming agent was added to neat polypropylene (PP) polymer, talc filled polypropylene (PP-T) composite and talc filled polypropylene/ethylene-propylene-diene blend (PP-T-EPDM) composite materials at the ratio of 1% and 2% by weight. The influence of foaming agent content on the mechanical and cellular properties of both neat PP polymer and PP composites was investigated. The results showed that the tensile strength, tensile modulus, impact strength, hardness, cell diameter, foam density and viscosity values and skin layer thickness decreased while volume expansion ratio increased with the increment in chemical blowing agent content.

Natural rubber/wood composite foam: Thermal insulation and acoustic isolation materials for construction

Abstract: With the advances in the field of civil construction and the world population growth, the development of policies is necessary for the management and reuse of generated residue. Thus, the present work proposes the use of expanded natural rubber as a polymeric matrix incorporated with eucalyptus filler as a reinforcing filler for the production of composites. Thermal insulation capacity was determined by the transient plane source and acoustic method by impedance tube. NR/W40 foam showed enhanced the acoustic insulation capacity. The maximum absorption of NR/W40 was 0.83, at 3257 Hz, which is three times higher than natural rubber foam. Highly inhomogeneous cell structures were observed with large, interconnected pores, improving the acoustic performance. Sound absorption coefficient for natural rubber foam with 40% wood (0.83 ± 0.046) was similar to PU foam (0.97 ± 0.009) with 20 mm in thickness, a density of 47 kg/m3 and 98% open cell content it is a well-known acoustic absorbent in the building sector. The NR/W40 sample recorded the best acoustic performance among the NR foams analyzed in this work, maintaining good sound absorption above 1500 Hz, demonstrating a possibility of wood reuse as a filler in based-rubber foam for acustic insulation.