Development and investigation of the applicability of computed tomography data-based modelling technique for polymeric high-density foams

As foams have become very important in several areas and since characterizing their properties is a crucial task, a finite element simulation model for high-density closed cell foams based on computed tomography (CT) measurements is developed. The model includes realistic microstructural features like cell size distribution due to the utilization of CT data. Moreover, a ‘skin-core-skin’ microstructure resulting from the manufacturing process (injection moulding) of the foams is also considered in the model. The mechanical behaviour of the foam’s core layer under tension and compression load is characterized based on the microstructural model to develop constitutive material models of the foam. These constitutive models enable further mechanical characterization of the foam with less computational effort. Compression and bending test simulations of injection moulded foams with three different densities are validated with corresponding experimental results. Thus, conclusions can be drawn regarding the reliability, applicability and possible further extensions of the high-density foam model.

Effect of rare earth nucleating agent on supercritical CO2 foaming behavior of block copolymerized polypropylene

The rare earth nucleating agent was used to modify block copolymerized polypropylene (PPB) in foaming process. The results show that the crystallization of PPB and the melting temperature of β-crystal increased gradually with increased β-crystal nucleating agent content. The total crystallinity decreased with amount of addition increasing, and the relative content of β-crystal increased first and then decreased. When β-crystal nucleating agent content was 0.4 wt%, the relative β-crystal content reached the maximum value of 95.27%, and the final crystal grain refinement significantly. The addition of rare earth β-crystal nucleating agent has a good effect on improving the uniformity of foam cells. Under the same content of β-crystal nucleating agent and pressure, the average cell diameter and expansion ratio increased with the saturation temperature increasing. After the foaming temperature reaches 155°C, the expansion ratio began to decrease, which was also consistent with the changed trend of relative β-crystal content. At the same content of temperature and relative β-crystal, as the foaming pressure increased, the cell diameter decreased gradually, and the expansion ratio increased first, and then decreased.

Theoretical modeling of longitudinal piezoelectric characteristic for cellular polymers

Efficient energy harvesting is a difficult challenge that consists in the development of systems allowing charging autonomous and low-power devices. In addition to traditional piezoelectric polymers, mono-crystals, and ceramics, cellular electrets offer consistent solutions by converting wasted vibration energy from the environment to usable electrical energy. This paper presents an electromechanical model to study the energy harvesting capability of cellular polymers. The theoretical study models the response of these materials to investigate the effect of different parameters on the piezoelectric coefficient d33, particularly. The model considers the percentage of porosity, surface charge density in each polymer–gas surface, the properties of the polymer matrix and the gas encapsulated in the pores, and the Young’s modulus of the porous film. For poly(ethylene-co-vinyl acetate), the results showed that the piezoelectric performance of the film declines with the increase of the film thickness. However, the variation of the d33 as a function of the percentage of porosity is exponential and can achieve 4.24 pC/N for a porosity of 80%. Compared to a previously published experiment, the theoretical results have proven a good agreement with only 3.3% error.

Preparation and properties of high melt strength PBS and its environmentally friendly foaming materials

In order to improve the melt strength of Poly(butylene succinate) (PBS) resin, the silane graft-crosslinked PBS copolyester materials were prepared by melt blending method with vinyltriethyl silane as graft material and benzyl peroxide (BPO) as initiator. At the same time, the environmentally friendly compound foaming agent (citric acid and sodium bicarbonate) was used as foaming agent. The results showed that the tensile properties and melt strength of PBS resin were greatly improved after silane grafting and cross-linking, and the graft and cross-linking reaction between PBS resin and silane occurred, forming a three-dimensional space network structure, and the viscosity and elasticity of polymer melt was changed, which increased the entropy elasticity of the material and strengthened the polymer melt strength. The additional amount of compound foaming agent and the cross-linking degree of material had important influence on the diameter and distribution of PBS foaming material.

Optimization of structural parameters on hollow spherical cells manufactured by Fused Deposition Modeling (FDM) using Taguchi method

There is a growing need for 3D printing of polymer structures in a cost-effective way and green. This study presents an experimental approach to investigate structural parameters effects on mechanical properties of polylactic acid (PLA) hollow-sphere structures manufactured with fused deposition modeling (FDM). The mechanical behavior characteristics of square_hexagonal stacking, closed_open porosity and parallel_perpendicular compression direction compared to the direction of manufacture under quasi-static uniaxial compression are examined using Taguchi method. The S/N ratio analysis and the Analysis of Variance (ANOVA) were used to find the optimal parameters that improve the mechanical properties (Young modulus, yield strength) and to provide a significant ranking of the different parameters analyzed in this paper. It was found that the optimum level and significance of each process parameter vary for “hexagonal cells,” “open porosity” and “parallel direction.” The optimal values of the results give a Young modulus E of 90.12 MPa and a yield strength [Formula: see text] of 3 MPa. Furthermore, the experimental results further reveal that the porous structure with the loading direction that is parallel to the direction of manufacture, has a higher strength and a progressive collapse of the cells to those with a perpendicular direction.

Morphological evaluation of microcellular foamed composites developed through gas batch foaming integrating Fused Deposition Modeling (FDM) 3D printing technique

In this article, the development of microcellular structure foams has developed by integrating the two successful and existing technologies, namely CO2 gas batch foaming and Fused Deposition Modeling (FDM) 3D printing technique. It is a novel approach to manufacture complex design porous products for customized applications. The eventual cell morphologies of the extruded 3D printing filament depends on the process parameters pertaining to both microcellular foaming and 3D printing processes. Further, morphological study has been conducted to evaluate the cell morphologies of the 3D printing filament developed through customized FDM setup. During this process, the significance of various process parameters including saturation pressure, saturation time, desorption time, feed rate and extrusion temperature were thoroughly studied. To pursue this study base material used was acrylonitrile butadiene styrene (ABS). The 3D printed filaments consisted of cells with an average cell size in the range of 2.3–276 µm and the average cell density in the range of 4.7 × 104 to 4.3 × 109 cells/cm3. Finally, it has found that by controlling the process parameters different cell morphologies can be developed as per the end application.

Development and investigation of the applicability of microstructural models for polymeric low density foams directly obtained from computed tomography data

Nowadays, there are several methods to obtain simulation models for foams which consider important microstructural features. This research study presents a method to obtain low density foam models directly from computed tomography (CT) data. Finite element meshes are created from CT measurement results of a polypropylene extrusion foam with two different densities. Sensitivity studies with regard to the tension behaviour are performed with the microstructural models. The study shows that the tension behaviour highly depends on the examined area of the foam because the microstructure and density vary through the foam. Furthermore, the simulation results are validated with experimental results. The validation shows that the tension behaviour of the investigated foams characterised by the simulation approach is in good agreement with the experimentally observed behaviour and that specific microstructural characteristics (e.g. anisotropic cell shapes) are captured in the model.

A study on fabrication of nanocomposite polyethylene foam through extrusion foaming procedure

Foaming a polymer not only turns it into a lightweight material but also gives some special properties to it. However, the most important issue is controlling the foaming process to achieve a desirable structure with high cell density and low relative density. In the present study, the extrusion foaming process of polyethylene was studied through stepwise amendments. An innovative extrusion system was designed and implemented to produce extrusion foams under different material and process conditions using N2 as blowing agent. In the first step, the final cooling condition was investigated. The air-cooling condition led to a higher cell density/lower cell size compared to the water-cooling condition although a higher relative density was obtained. In the second step, the effects of the addition of talc and the synergetic effect of talc/nanoclay at different contents were investigated in detail. The hybrid of talc/nanoclay had a noticeably improving effect on the cellular structure. In the third step, the effects of processing parameters including the die temperature and screw speed were studied on the foam properties. Finally, up to 49.4% decrease in the relative density of samples was observed, also cell densities up to 2.5 × 104 cell/cm3 and cell sizes as small as 280 µm were achieved.

An efficient and environment friendly bio-based polyols through liquefaction: Liquefaction temperature and catalyst concentration optimization and utilized for rigid polyurethane foams

Aiming towards the liquefaction of paddy straw was accumulation as well as providing a technically viable route leading to preservation of the natural resources and environment, the paddy straw was chemically liquefied. Paddy straw were liquefied into bio-based polyol in the presence of castor oil and blend of castor and karanja oil as depolymerizing agent and P-Toluene sulfonic acid as catalyst. Liquefied product was characterized by chemical as well as analytical techniques. The agricultural waste base paddy straw was eventually converted into polymeric precursor (polyol) monomer with nearly 80 to 95% yield by employing 2% catalyst concentration and at optimized temperature of 180°C. Synthesized polyol can be utilized further in formulating high quality rigid polyurethane foams. The foams were characterized in terms of their physical, mechanical, thermal and morphological properties. All foams exhibit good compressive strengths and thermal stability. Thermal conductivity of foams varied between 0.012 and 0.023 Kcal/mh°C, with the lowest being of foam from liquefied (LP), making it suitable for utilization as an insulation material.

Morphological, thermal and mechanical properties of polypropylene foams via rotational molding

In this work, polypropylene (PP) was foamed via rotational molding using a chemical blowing agent (CBA) based on azodicarbonamide over a range of concentration (0 to 0.5% wt.). The samples were then analyzed in terms of morphological, thermal and mechanical properties. The morphological analysis showed a continuous increase in the average cell size and cell density with increasing CBA content. Increasing the CBA content also led to lower foam density and thermal conductivity. Similarly, all the mechanical properties (tension, flexion and impact) were found to decrease with increasing CBA content. Finally, the efficiency of the rotomolding process was assessed by producing neat PP samples via compression molding. The results showed negligible differences between the rotomolded and compression molded properties at low deformation and rate of deformation indicating that optimal rotomolding conditions were selected.