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To increase the degradation rate of poly(lactic acid) (PLA), soy protein concentrate (SPC) was introduced via melt compounding using a self-developed, co-rotating, non-twin-screw extruder. Poly(2-ethyl-2-oxazoline) (PEOX) and diphenyl methane diisocyanate (MDI) were added to plasticize the melt and improve the compatibility between PLA and SPC. The PLA/SPC blends were subsequently foamed using supercritical carbon dioxide (C[O.sub.2]) as a blowing agent to produce porous composites. The involvement of SPC promoted cold crystallization of PLA but reduced the thermal stability of the blends. PLA showed a strong interfacial bonding with modified SPC, and the SPC formed continuous three-dimensional networks when its proportion reached 30 wt%. In the foaming process, SPC domains acted as heterogeneous nucleation sites, which resulted in enhanced cell densities and reduced cell diameters. The PLA/SPC (70:30) sample showed the finest cell structure due to the presence of the SPC network. For the same blends, increasing the foaming pressure from 16 to 20 MPa enhanced the cell density by about 5 times. The water absorption rate and the biodegradation rate of the PLA/SPC foams were much higher than that of neat PLA due to the hydrophilicity of SPC and the porous structure of the foams., INTRODUCTION In the recent years, biobased polymers have received great interest as renewable plastics because of their biodegradability and biocompatibility [1-4]. PLA, which is a compostable polymer derived from renewable [...]

Microcellular injection molding can fabricate lightweight, dimensionally stable plastic parts while using less material and energy. This article investigates a new process using water vapor as the physical blowing agent and comparing two kinds of nucleating agents, namely, cubic sodium chloride (NaCl) and non-uniform active carbon (AC). The effects of different nucleating agents on the surface roughness, mechanical properties, and microstructure of solid and foamed parts were characterized. Compared with typical microcellular injection molded parts, water vapor-foamed polycarbonate (PC)/NaCl had a smooth surface comparable to that of solid parts, whereas foamed PC/AC had desirable specific mechanical properties as well as an attractive average weight reduction of 16.4 wt%. Low density and non-uniform AC particles, used as a nucleating agent and reinforcement, improved the microcellular structure. Based on PC molecular weight measurement, the melt processing and water vapor-foaming processes did induce a slight amount of thermal degradation and hydrolytic degradation, respectively., INTRODUCTION The commercially available microcellular injection molding process blends supercritical fluids (SCF; usually nitrogen or carbon dioxide) with polymer melts in the injection molding machine barrel to create a single-phase [...]

PLA/PEG/NaCl blends were melt-blended followed by gas foaming and particle leaching process to fabricate porous scaffold with high porosity and interconnectivity. A homemade triple-screw compounding extruder was used to intensify the mixability and dispersion of NaCl and PEG in the PLA matrix. Supercritical carbon dioxide was used as physical blowing agent for the microcellular foaming process. Sodium chloride (NaCl) was used as the porogen to further improve the porosity of PLA scaffold. This study investigated the effects of PEG and NaCl on the structure and properties of the PLA-based blend, as well as the porosity, pore size, interconnectivity, and hydrophilicity of porous scaffolds. It was found that the incorporation of PEG and NaCl significantly improved the crystallization rate and reduced viscoelasticity of PLA. Moreover, scaffolds obtained from PLA/PEG/NaCl blends had an interconnected bimodal porous structure with the open-pore content about 86% and the highest porosity of 80%. And the presence of PEG in PLA/NaCl composite improved the extraction ability of NaCl particles during leaching process, which resulted in a well-interconnected structure. The biocompatibility of the porous scaffolds fabricated was verified by culturing fibroblast cells for 10 days., INTRODUCTION Tissue engineering, an interdisciplinary field that aims to provide therapeutic treatments to maintain, restore, or replace damaged tissues and organs, has been a focus of intense research over the [...]

Biodegradable polylactic acid (PLA) was compounded with thermoplastic polyurethane (TPU) by twin-screw extrusion at weight ratios of 90/10, 80/20, 70/30, and 60/ 40. The blends were investigated based on their phase morphology, thermal and mechanical properties, and shape memory properties. The tensile results showed that PLA was successfully toughened by TPU. When the TPU content was 40%, the elongation-at-break increased to 400%. The SEM morphology showed that TPU was dispersed uniformly in the PLA matrix; DMA and DSC results indicated that the two polymers were immiscible. Most interestingly, it was found that the blends exhibited a shape memory behavior and, unlike most of the existing shape memory polymers (SMPs), the PLA/TPU blends could be deformed at room temperature without an extra heating and cooling step. During the deformation process, TPU acted as a toughening agent that prevented the PLA/ TPU blends from breaking; thus, the temporary shape could be kept and internal stress was stored in the blends. Upon heating to above the glass transition temperature of PLA (about 60°C), the deformed parts regained their original shapes quickly along with the release of the stress., INTRODUCTION Polylactic acid (PLA), an aliphatic polyester, is a biodegradable polymer derived from renewable resources such as com and sugar beets. It has attracted great interest in both academia and [...]

Injection foaming is an method for mass producing lightweight, foamed plastic components with excellent dimensional stability while using less material and energy. In this study, a novel injection foaming method employing supercritical C[O.sub.2] (scC[O.sub.2]) and water as coblowing agents was developed to produce thermoplastic polyurethane (TPU) components with a uniform porous structure and no solid skin. Various characterization techniques were employed to investigate the cell morphology, crystallization behavior, and static and dynamic mechanical properties of solid injection molded samples, foamed samples using C[O.sub.2] or water as a single blowing agent, and foamed samples using both C[O.sub.2] and water as coblowing agents. When compared with C[O.sub.2] foamed samples, samples produced by the coblowing method exhibited much more uniform cell morphologies without a noticeable reduction in mechanical properties. Moreover, these TPU samples had almost no skin layer, which permitted the free transport of nutrients and waste throughout the samples. Such a mass-produced, skin-free structure is desirable in tissue engineering. In this study, the biocompatibility of the scaffolds was confirmed and the effect of these blowing agents on the TPU foaming behavior was studied., INTRODUCTION Synthetic and natural polymers have been used in tissue engineering to prepare temporary scaffolds for transplanted cells for tissue recovery and organ replacement. A wide variety of fabrication methods [...]

This article presents a new process for producing microcellular injection molded plastic parts using water as the physical blowing agent and microscaled particles as the cell nucleating agents. Distilled water with dissolved salt were fed through the hopper of an injection molding machine at a preset rate and mixed with polycarbonate (PC) in the machine barrel. Microcellular PC tensile bars were then injection molded with different shot volumes, water/salt solution feed rates, and salt concentrations. Tiny salt crystals of 10-20 µm recrystallized during molding acted as nucleating agents in the PC foamed parts. The surface roughness, mechanical properties, and microstructure of the solid and foamed parts were measured and compared with microcellular injection molded parts using supercritical fluid (SCF) nitrogen as the physical blowing agent. At a similar weight reduction of about 10%, the water foamed PC parts have a smooth surface comparable to that of solid injection molded parts. They also possess similar, if not better, mechanical properties compared to SCF nitrogen foamed PC parts. Without the nucleating agent, PC/water foamed parts exhibit much larger and fewer bubbles within the molded parts. POLYM. ENG. SCI., 52:1464-1473, 2012. [C] 2012 Society of Plastics Engineers, INTRODUCTION Microcellular injection molding is capable of fabricating lightweight. dimensionally stable plastic parts while using less material and saving energy. In the most widely used commercial microcellular injection molding process. [...]

To increase the degradation rate of poly(lactic acid) (PLA), soy protein concentrate (SPC) was introduced via melt compounding using a self‐developed, co‐rotating, non‐twin‐screw extruder. Poly(2‐ethyl‐2‐oxazoline) (PEOX) and diphenyl methane diisocyanate (MDI) were added to plasticize the melt and improve the compatibility between PLA and SPC. The PLA/SPC blends were subsequently foamed using supercritical carbon dioxide (CO2) as a blowing agent to produce porous composites. The involvement of SPC promoted cold crystallization of PLA but reduced the thermal stability of the blends. PLA showed a strong interfacial bonding with modified SPC, and the SPC formed continuous three‐dimensional networks when its proportion reached 30 wt%. In the foaming process, SPC domains acted as heterogeneous nucleation sites, which resulted in enhanced cell densities and reduced cell diameters. The PLA/SPC (70:30) sample showed the finest cell structure due to the presence of the SPC network. For the same blends, increasing the foaming pressure from 16 to 20 MPa enhanced the cell density by about 5 times. The water absorption rate and the biodegradation rate of the PLA/SPC foams were much higher than that of neat PLA due to the hydrophilicity of SPC and the porous structure of the foams. POLYM. ENG. SCI., 59:1753–1762, 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Polystyrene/multi-wall carbon nanotube composite with an interconnected honeycomblike structure was prepared by firstly coating the surface of the polystyrene pellets with multi-wall carbon nanotube, and sequentially welded through an ultrasound vibration technique. The mechanical and morphological properties of as-prepared composite were investigated in various measurements. It was found that an aggregative and honeycomb-like morphology of multi-wall carbon nanotube existed in the polystyrene/multi-wall carbon nanotube composite according to the polarized optical microscopic and scanning electron microscopic results; the ultrasound vibration could benefit to the performance of flexural strength. Furthermore, different composite foams were studied in this work, employing supercritical carbon dioxide as a blowing agent. Compared to other foams prepared by the conventional methods, the compressive strength of the foams derived from as-described novel method, was significantly improved. Also, being ascribed to this interconnected structure by coating carbon nanotube on polystyrene pellets, good electrical conductivity of 0.05-0.11 S/m was achieved in the novel composite foams. [ABSTRACT FROM AUTHOR]