Study on Foaming Quality and Impact Property of Foamed Polypropylene Composites

Influence of temperature distribution on the foaming quality of foamed polypropylene composites

The foamed polypropylene (PP) composites were prepared by injection molding process. Fourier’s law and software were used to calculate and simulate the internal temperature distribution of PP composites, respectively, and the influence of the temperature distribution on the foaming quality of foamed PP composites was further analyzed. The result showed that the calculative and simulated results of temperature distribution in different thermal transfer directions had great reproducibility. In different isothermal planes, the temperature from the nozzle to the dynamic mold gradually decreased. The isothermal plane with a temperature of 370.36 K had a better foaming quality, average diameter of cell and cell density were 28.46 µm and 3.7 × 1010 cells·cm−3, respectively. In different regions of the same isothermal plane, the temperature gradually decreased from the center to the edge. The foaming quality in the region (c) at a temperature of 335.86 K was ideal, and the average diameter of cell and the cell density were 26.5 µm and 2.39 × 1010 cells·cm−3, respectively. This work could provide prediction for improving the foaming quality of foamed polyolefin composites.

Mechanical and Adsorptive Properties of Foamed EVA-Modified Polypropylene/Bamboo Charcoal Composites

Due to its excellent adsorption and humidity control function, bamboo charcoal (BC) has often been mixed with polypropylene (PP) to produce PP/BC composites for interior paneling applications. However, due to the poor foaming quality of PP, PP/BC composites suffer as a result of their high density, which limits their scope of use. Here, to improve its foaming quality, PP was modified with ethylene vinyl acetate (EVA), and then the EVA-modified PP (E-PP) was mixed with different contents of BC (0 wt.%–50 wt.%), as well as foaming agent (Azodicarbonamide, AC) and its auxiliaries (ZnO, Znst), in a twin-screw extruder, followed by hot-pressing at high temperature to obtain foamed E-PP/BC composites. The resulting composites showed good porosity and pore distribution with an increase of BC content by up to 20%. Further increase in the BC content seemed to cause the foaming performance to decrease significantly. The product density and adsorption rate increased, while the mechanical strength decreased with increasing BC content. At a BC content of 40 wt.%, the foamed E-PP/BC composite showed the best combined performance, with a density of 0.90 g/cm³, 24-h formaldehyde adsorption rate of 0.48, and bending strength of 11.59 MPa.

Injection Molded PP Foams Using Food Ingredients for Food Packaging Applications

A new approach to the creation of polypropylene (PP) based foaming materials was developed using food grade foaming agents that were coated on the PP pellets. More specifically, sodium bicarbonate and organic acids were used to coat PP pellets using either polyethyleneoxide (PEO) or lipid esters as coating stabilizers. In order to overcome the problem of the thermal decomposition of sodium bicarbonate at temperatures lower than the PP melting temperature, which makes the direct foaming during melt mixing impossible, the proposed methodology was proved quite efficient. Thus, new PP masterbatches were prepared, where the foaming agents were incorporated as coating at PP pellets at contents up to 10%, and initially used in Lab scale injection machines in order to find the best combination of materials that resulted in the production of foamed articles. Subsequently selected material combinations were tested in an industrial scale injection molding machine, where an optimization of the injection parameters was attempted. The outcome of this was the production of PP articles with significantly increased void fraction, up to 14%, decreased thermal conductivity, up to 20%, and various pore sizes as was observed via microscopic examination using SEM and CLSM.

Polymeric foams from recycled thermoplastic poly(ethylene terephthalate)

With the increase use of plastics, there is currently a concern with the waste of materials, resulting in a series of challenges and opportunities for the waste management sector. In the present work, poly(ethylene terephthalate) (PET) foam was produced from recycled PET (RPET) from used water bottles. The recycled material was manually prepared and foamed in batches with the assistance of nitrogen gas as the physical blowing agent. RPET was characterized using Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). The influence of the pressure on the foam formation was studied and the results obtained showed that this variable influences the final product characteristics. To evaluate the behavior of the foams, their morphology, response to deformation when subject to compression and their thermal conductivities were studied. The morphology analysis showed that operating at higher-pressure results in bigger pore size but also in an increased pore size heterogeneous distribution, and foams that exhibit a higher thermal conductivity.

Characterization and Model Validation for Large Format Chopped Fiber, Foamed, Composite Structures Made from Recycled Olefin Based Polymers

The purpose of this research is to predict the material performance of large format foamed core composite structures, such as crossties or structural timbers, using only constitutive properties. These structures are fabricated from recycled post-consumer/post-industrial waste composed of High-Density Polyethylene (HDPE) and Glass Filled Polypropylene (GFPP). A technical challenge in predicting the final part performance is the mathematical correlation between the microstructural variations and the macroscopic responses as a function of fiber aspect ratio, cell density, and constitutive properties of the polymer blend. The structures investigated have a dense and consolidated outer shell and a closed cell foamed core. The non-linear shell and the foamed core material properties are analyzed with micromechanics models, and the reference stress of the shell and core is predicted using a modified Rule of Mixtures model. The predicted properties are used as the inputs for a Finite Element Analysis (FEA) model, and the computational results are compared to experimental four-point bend test results for sixteen samples performed on a 120-kip compression stage. The results show that the mean of the characterized deflections from the four-point bend tests did not show any variations for an isotropic and transversely isotropic model using a linear analysis. This model was then extended to a non-linear analysis using the Ramberg–Osgood model to predict the full crosstie four-point bend test behavior. The FEA model results show a deviation of 2.45 kN compared to the experimental variation of 3.58 kN between the samples measured.

High-Performance Polymer Foams by Thermally Induced Phase Separation

Macroporous, low-density polyetheretherketone, polyetherketoneketone, and polyetherimide foams are produced using a high-temperature, thermally induced phase separation method. A high-boiling-point solvent, which is suitable to dissolve at least 20 wt% of these high-performance polymers at temperatures above 250 °C, is identified. The foam morphology is controlled by the cooling procedure. The resulting polymer foams have porosities close to 80% with surface areas up to 140 m² g^-1 and elastic moduli up to 97 MPa.

Foams with Enhanced Ductility and Impact Behavior Based on Polypropylene Composites

In this work, formulations based on composites of a linear polypropylene (L-PP), a long-chain branched polypropylene (LCB-PP), a polypropylene-graft-maleic anhydride (PP-MA), a styrene-ethylene-butylene-styrene copolymer (SEBS), glass fibers (GF), and halloysite nanotubes (HNT-QM) have been foamed by using the improved compression molding route (ICM), obtaining relative densities of about 0.62. The combination of the inclusion of elastomer and rigid phases with the use of the LCB-PP led to foams with a better cellular structure, an improved ductility, and considerable values of the elastic modulus. Consequently, the produced foams presented simultaneously an excellent impact performance and a high stiffness with respect to their corresponding solid counterparts.

Graphene Foam Cantilever Produced via Simultaneous Foaming and Doping Effect of an Organic Coagulant

Inspired by the role of cellular structures, which give three-dimensional robustness to graphene structures, a new type of graphene cantilever with mechanical resilience is introduced. Here, NH₄SCN is incorporated into graphene oxide (GO) gel using it as a coagulant for GO fiber self-assembly, a foaming agent, and a dopant. Subsequent thermal treatment of the GO fiber at 600 °C results in the evolution of gaseous species from NH₄SCN, yielding internally porous graphene cantilevers (NS-GF cantilevers). The results reveal that NS-GF cantilevers are doped with N and S and thus exhibit higher electrical conductivity (150 S cm^-1) than that of their nonporous counterparts (38.4 S cm^-1). Unlike conventional fibers, the NS-GF cantilevers exhibit mechanical resilience by bending under applied mechanical force but reverting to the original position upon release. The tip of the NS-GF cantilevers is coated with magnetic Fe₃O₄ particles, and fast mechanical movement is achieved by applying the magnetic field. Since the NS-GF cantilevers are highly conductive and elastic, they are employed as bendable, magnetodriven electrical switches that could precisely read on/off signals for >10 000 cycles. Our approach suggests a robust fabrication strategy to prepare highly electroconductive and mechanically elastic foam structures by introducing unique organic foaming agents.

Cellulose Acetate and Supercritical Carbon Dioxide: Membranes, Nanoparticles, Microparticles and Nanostructured Filaments

Cellulose acetate (CA) is a very versatile biocompatible polymer used in various industrial sectors. Therefore, depending on the application, different morphologies are required. Different processes at industrial scale are commonly employed to obtain CA micro or nanoparticles (discontinuous structures) or CA membranes (continuous structures with discontinuities). In this work, two supercritical carbon dioxide (scCO₂) based techniques, such as the semi-continuous supercritical antisolvent process (SAS) and the supercritical fluid phase inversion process, in which scCO₂ plays the role of antisolvent, were employed. Varying the kind of organic solvent used to prepare the polymeric solution, the polymer concentration, and operating pressure and temperature, it was possible to tune the characteristics of the obtained material. In particular, using acetone as the organic solvent, filaments constituted by nanoparticles, expanded microparticles, nanoparticles with a mean diameter lower than 80 nm, and microporous membranes were obtained, varying the operating conditions. The attainment of spherical micron-sized particles was instead achieved using a mixture of acetone and DMSO as the organic solvent. Therefore, the versatility of the supercritical carbon dioxide-based techniques has been confirmed, and it was possible to obtain, using a single experimental plant, various morphologies of cellulose acetate (with controllable particles' or pores' diameters) by varying the operating conditions.

Polymeric Foams

Advances in nanotechnology have boosted the development of more efficient materials, with emerging sectors (electronics, energy, aerospace, among others) demanding novel materials to fulfill the complex technical requirements of their products [...].

Investigation of the Constitutive Model of W/PMMA Composite Microcellular Foams

Investigating the constitutive relationship of a material can provide better understanding of the mechanical properties of a material and has an irreplaceable effect on optimizing the performance of a material. This paper investigated a constitutive model for tungsten/polymethyl-methacrylate (W/PMMA) composite microcellular foams prepared by using melt mixing and supercritical carbon dioxide foaming. The stress-strain relationships of these foams with different W contents were measured under static compression. The elastic modulus and compressive strength values of the foams were remarkably greater than those of the pure PMMA foams: at a W content of 20 wt %, these values were increased by 269.1% and 123.9%, respectively. Based on the Maxwell constitutive model, the relevant coefficients were fitted according to the experimental data of different relative densities and W contents in quasi-static compression. According to the numerical relationships between the relevant coefficients and the relative densities and W contents, the quasi-static mechanical constitutive model of W/PMMA composite microcellular foams with W contents of 0~60 wt % and relative densities of 0.15~0.55 were predicted. This study provided basic data for the optimal design of the W/PMMA composite microcellular foams and proposed a method for investigating the mechanical properties of composite microcellular foam materials.

Recent Trends of Foaming in Polymer Processing: A Review

Polymer foams have low density, good heat insulation, good sound insulation effects, high specific strength, and high corrosion resistance, and are widely used in civil and industrial applications. In this paper, the classification of polymer foams, principles of the foaming process, types of blowing agents, and raw materials of polymer foams are reviewed. The research progress of various foaming methods and the current problems and possible solutions are discussed in detail.

Effect of Mold Temperature on the Impact Behavior and Morphology of Injection Molded Foams Based on Polypropylene Polyethylene⁻Octene Copolymer Blends

In this work, an isotactic polypropylene (PP) and a polyethylene–octene copolymer (POE) have been blended and injection-molded, obtaining solids and foamed samples with a relative density of 0.76. Different mold temperature and injection temperature were used. The Izod impact strength was measured. For solids, higher mold temperature increased the impact resistance, whereas in foams, the opposite trend was observed. In order to understand the reasons of this behavior, the morphology of the elastomeric phase, the crystalline morphology and the cellular structure have been studied. The presence of the elastomer near the skin in the case of high mold temperature can explain the improvement produced with a high mold temperature in solids. For foams, aspects as the elastomer coarsening in the core of the sample or the presence of a thicker solid skin are the critical parameters that justify the improved behavior of the materials produced with a lower mold temperature.