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This paper presents the foaming behaviors of high-density polyethylene (HDPE)-based and polypropylene (PP)-based wood fiber composites with a small amount of nanosized clay. Melt compounding was used to prepare various types of clay-filled, wood fiber composites, such as intercalated and exfoliated clay composites. Their morphology was determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The extrusion foaming was conducted using N2 as the blowing agent. The cell nucleation and growth behaviors of composite foams were studied while varying temperature, pressure, wood fiber content, and clay content. The effects of clay content and exfoliation degree on the final cell morphology of wood fiber/polyolefin/clay nanocomposite foams were identified.

Polymers are often blended to create compounds with new or enhanced properties in order to compensate for an individual polymer's weakness or lack of inherent properties. In the field of polymer foaming, polymer blends are also used to generate fine-cell structures via heterogeneous nucleation. Recently, an interest in physical blowing agents, such CO2 and N2, has increased because of their low impact on the environment. It has thus become additionally important to pursue research on the foaming of polymer blends employing these particular physical blowing agents in an effort to keep up with the demand for environmentally friendly products. In this study, thermoplastic polyolefin (TPO) blends were prepared with polypropylene (PP) and a metallocene-based polyolefin elastomer (POE) using twin-screw extruders and a batch mixer.

This research presents a fundamental study of the interaction between chemically modified wood fibers and high density polyethylene (HDPE) to develop wood fiber/HDPE composites with satisfactory performance. This paper investigates the effects of the interfacial properties of HDPE and wood fibers on the rheological properties and foaming behavior of the composites. The surface characteristics of wood fiber were modified by treating the fiber with trialkoxy silane. The effectiveness of chemical surface modifications of wood fiber was characterized using FT-IR. The effect of the interfacial interaction on the foaming behavior was studied via extrusion foaming with a physical blowing agent. The rheological property of the composites with a different interfacial structure were also evaluated by using dynamic oscillatory rheometer.

This study compared the mechanical properties of rice hull/high density polyethylene composites with those of maple wood-based counterparts. In addition, the effects of maleated polymers on the mechanical properties of rice hull and maple wood composites were investigated. Six types of maleated polymers (coupling agents) were used to improve mechanical properties, of the composites, especially notched Izod impact strength. The results suggested that the maple wood composites showed higher strength, modulus and impact strength than the rice hull composites. The results also indicated that maleated thermoplastic elastomers increased notched Izod impact strength of both composites dramatically. However, it was found that Maleated metallocene polyethylene was the most effective coupling agent that increased notched impact strength without sacrificing tensile and flexural strength.

Thermoplastic Vulcanizate (TPV) is a special class of Thermoplastic Elastomers (TPEs) made of a rubber/plastic polymer mixture in which the rubber phase is highly vulcanized. It is prepared by melt mixing a thermoplastic with an elastomer and by in-situ crosslinking of the rubber phase. Currently, TPV is replacing EPDM rubber dramatically because of the impressive advantages for automotive sealing applications. Some of the advantages of TPV compared to that of EPDM rubber are good gloss, recyclability, improved colorability, shorter cycle time and design flexibility. The development of TPV foaming technology is to fulfill the requirement of achieving lower cost, lighter weight and better fuel economy. Foaming of TPV has not been investigated extensively.

TPO is being used to make automotive parts for its number of advantages: i) low temperature flexibility and ductility, ii) excellent impact/stiffness/flow balance, iii) excellent weatherability, and iv) free-flowing pellet form for easy processing, storage, and handling. However, by foaming TPO, due to its higher rigidity-to-weigh ratio, it would offer additional advantages over the solid counterparts in terms of reduced weight, reduced material cost, and decreased fuel usage without compromising their performance. Since a major component in TPO is polypropylene (PP), understanding PP foaming behaviours is an important step towards understanding TPO foaming. For foam materials, cell density and cell size are two significant parameters that affect their material properties. In this research, we observed the cell nucleation and initial growth behaviours of PP foams blown with CO2 under various experimental conditions in a batch foaming simulation system.

Foaming of a thermoplastic polyolefin (TPO) is gaining interests because of its superior mechanical properties of foamed automotive parts, such as lightweight and high performance to weight ratio, etc. In this context, understanding of the thermophysical properties of PP/gas and TPO/gas mixtures is critically important. This paper will present the newly developed experimental technique to accurately measure the swelling of PP and TPO due to gas dissolution at elevated temperatures and pressures. Our technique measures the geometry of the pendent drop accurately from the captured images to obtain the volume swelling data. It determines the boundary location of the polymer/gas sample accurately by magnifying the sample drop locally along its edge before capturing the image. The automated high-precision XY stage is chosen as the platform to control the motion of the CCD camera.

This research investigates the foaming behaviors of polypropylene (PP) and PP/clay nanocomposites blown with supercritical CO2. In this context, special attention is paid to the effects of varied clay content on the foamed structures. First, a master batch of nanocomposites with 1% and 5% clay are prepared; the nanocomposites are then characterized using X-Ray Diffraction (XRD) prior to and after their subjection to the foaming process. Subsequently, foaming experiments are conducted using supercritical CO2 as a blowing agent. The cell nucleation and expansion behaviors of the PP-based nanocomposite foams are studied at various clay contents and die temperatures. Finally, the effects of the clay content on the cell morphology, the cell density, and the expansion ratio of the PP/clay nanocomposite foams are identified.

Determination of the solubility of a blowing agent, i.e. supercritical N2, in polypropylene (PP) and elastomer material is crucial for achieving high-quality thermoplastic polyolefin (TPO) foams in automotive industry. A magnetic suspension balance (MSB) was employed in the experiments to measure the apparent solubility, while the swollen volume predicted by the Sanchez-Lacombe (SL) equation of state (EOS) was used to account for the buoyancy effect. The volume swelling of the polymer/gas mixture and the gas solubilities for both PP and polyolefin elastomer were discussed.

This paper discusses the development of lighter weight, superior acoustic performance and cost effective viscoelastic microcellular foams for the use in automotive passive noise control panels. The study incorporates the control of the foaming process for production of variable microcellular structures and morphologies for the novel foams under investigation. For that purpose, the foaming process was controlled for production of foam samples with various microcellular structures. Cross linked LDPE was used as a base material for the produced foams. Very high open-cell content (ranging between 43 - 95%), high microcellular cell densities (9E108 - 1.6E109 cells/cm3) and desired expansion ratios (3 - 9 folds) were successfully obtained. While the material is overly porous, it is noted that the unfoamed skins on the outer surfaces of the samples have prevented sound waves from penetrating the samples. Manual skin removal resulted in slight improvement in sound absorption testing.

Foaming of thermoplastic polyolefins (TPO) and thermoplastic elastomers (TPE) is gaining interest because of the lightweight and high performance to weight ratio of foamed automotive parts. Since foaming will occur mainly in the PP matrix in these PP-based automotive materials, understanding of the thermophysical properties of PP/gas mixtures is critically important. This paper will present a proposed methodology for measuring the swelling of polymer/gas mixtures. The preliminary experimental measurement of PP/N2 swelling at elevated temperatures and pressures will be discussed.

This paper demonstrates the effects of nano-clay on the microcellular foam processing of nylon. First, Nylon 6 nanocomposites with 1 wt% clay were prepared by a twin screw extruder. The nanocomposite structures were characterized by XRD and TEM. Nylon and its nanocomposites were foamed in extrusion using CO2. The cell morphologies of nylon and its nanocomposite foams were investigated. It appeared that the nano-clay not only enhanced cell nucleation, but also suppressed cell deterioration in the microcellular foaming of nylon.

Determination of the solubility of a blowing agent, i.e. supercritical CO2 or N2, in polypropylene (PP) is crucial for achieving high-quality PP and thermoplastic polyolefin (TPO) foams. A magnetic suspension balance (MSB) was employed in the experiments to measure the apparent solubility, while the swollen volume predicted by the Sanchez-Lacombe (SL) equation of state (EOS) and Simha-Somcynsky (SS) EOS was used to account for the buoyancy effect. The gas solubilities for both linear and branched PP were calculated and the effects of branching on the swollen volume and gas solubility were discussed.