微孔塑料性能及制备

本文介绍了微孔塑料的设计思想、优异性能及其制备技术的发展情况 ,并着重分析了微孔塑料发泡成型的原理、技术关键及难点。     

一种打微孔改进结构的塑料编织袋

本文介绍了一种打微孔改进结构的塑料编织袋,包括依次由外至内设置的薄膜层、胶水层及塑料编织层,所述薄膜层、胶水层及塑料编织层的中部均阵列设有若干对应的第一微孔、第二微孔及第三微孔,所述第一微孔、第二微孔及第三微孔的分布密度均为2500个/m2,所述塑料编织层的左右两侧均阵列设有若干第四微孔,所述第四微孔的分布密度为2500个/m2。本技术打微孔改进结构的塑料编织袋容易生产、拉力强度高。     

微孔塑料性能及制备

本文介绍了微孔塑料的设计思想、优异性能及其制备技术的发展情况，并着重分析了微孔塑料发泡成型的原理、技术关键及难点。     

超临界二氧化碳发泡制备可控形貌的聚乳酸微孔材料

应用超临界CO2制备微孔聚乳酸,研究发泡条件和结晶度对微孔形貌的影响。结果表明,固定饱和压力与降压速率,升高温度有利于泡孔的生成;超过聚乳酸(PLA)完全熔融温度,无法生成泡孔;固定发泡温度与降压速率,提高压力有与温度类似的作用;由于PLA较低的熔体强度,降压速率的提高增大了生成泡孔之间的竞争,可形成孔道连通的微孔形貌;而PLA本身的结晶度很大程度上影响了PLA可发泡的区间,结晶不利于发泡。     

新型包装材料微孔塑料的研究

介绍了一种新型包装材料－－微孔塑料的两种成型方法：间歇成型法和连续挤出型法，并比较了各自的优缺点；对以ＣＯ２等惰性气体作为发泡剂的微孔塑料的加工过程中的各个阶段即气泡的成核、长大和定型进行了研究。     

全降解聚乳酸阻燃母料开发成功

我国在全生物降解聚乳酸（PLA）塑料阻燃技术开发上取得突破。记者2008年12月17日在石家庄金迪化工科技有限公司看到，全生物降解PLA塑料添加了该公司新研发的阻燃母料后，具有良好的耐热、难燃和低烟雾性能。这项阻燃技术的开发将提升聚乳酸的使用性能，为PLA生物降解塑料扩大应用领域创造了条件。     

国际要闻

全球塑料降解,回收技术层出不穷,1．生物降解增塑剂,2．法国采用PLA生物降解包装材料用于茶叶包装,3．英国公司塑料推出PLA薄膜制纸卡包装。     

聚乳酸超临界CO_2珠粒发泡研究进展

聚乳酸(PLA)是一种性能良好的新型环保塑料,而其发泡珠粒不仅具有PLA原料来源广、完全可降解、综合力学性能优良等优点,而且通过其微孔泡沫结构能满足高性能高级应用标准要求,同时减少材料使用、节约能源、环境友好和许多其他优势。文中综述了国内外聚乳酸珠粒的可发泡性能、泡孔调节、结晶调控和工艺条件等进展,总结并归纳了聚乳酸可完全降解和不可完全降解体系的复合改性方法,提出了目前存在的问题并比较了不同工艺条件的优缺点,对未来聚乳酸珠粒发泡技术的研究进行了展望。     

聚乳酸/酯化纤维素纳米晶体共混膜性能研究

以聚乳酸(PLA)为基体,酯化纤维素纳米晶体(ECNC)为添加剂,制备了PLA/ ECNC共混膜。探讨了原始纤维素纳米晶体(CNC)与ECNC对PLA膜的透光率、表面形貌、热稳定性、亲疏水性及力学性能的影响。结果表明,与CNC相比,ECNC与PLA的相容性提高,透光率、热稳定性及力学性能也显著增强;经酯化的纤维素纳米晶体能降低CNC的亲水性,从而增强与PLA的界面黏合力,使CNC在PLA共混膜中的质量分数由小于1%提高到5%。该PLA/ECNC共混膜在包装塑料领域具有潜力,为制备出性能更加优良的可降解包装用塑料提供了一种简单可行的方法。     

食品接触用聚乳酸降解性及其中的化学物质迁移

目的 介绍食品接触用聚乳酸(PLA)的降解行为及其中的化学物质的迁移情况,为食品接触用PLA的安全性和环保性,以及完善相关法规提供资料.方法 对PLA的特性,食品接触用PLA中重金属、添加剂和低聚物的迁移,PLA及其复合材料的降解等方面进行分析和总结.结果 PLA不仅有与传统塑料一样的安全隐患,还具有其自身降解产物迁移带来的安全问题.PLA的降解性受到多种因素的影响,除了受到自身性质的影响,还与共聚物的性质有关.结论 目前食品接触用PLA仍存在多种挑战,随着食品接触用PLA越来越广泛的应用,对其安全性和环保性进行深入研究非常必要.     

Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/PHBV) blends and PLA/PHBV/Clay nanocomposites

The morphology, microstructure, tensile properties, and dynamic mechanical properties of solid and microcellular poly(lactic acid) (PLA)/polyhydroxybutyrate-valerate (PHBV) blends, as well as PLA/PHBV/clay nanocomposites, together with the thermal and rheological properties of solid PLA/PHBV blends and PLA/PHBV/clay nanocomposites, were investigated. Conventional and microcellular injection-molding processes were used to produce solid and microcellular specimens in the form of ASTM tensile test bars. Nitrogen in the supercritical state was used as the physical blowing agent in the microcellular injection molding experiments. In terms of rheology, the PLA/PHBV blends exhibited a Newtonian fluid behavior, and their nanocomposite counterparts showed a strong shear-thinning behavior, over the full frequency range. An obvious pseudo-solid-like behavior over a wide range of frequencies in the PLA/PHBV/clay nanocomposites suggested a strong interaction between the PLA/PHBV blend and the nanoclay that restricted the relaxation of the polymer chains. PLA/PHBV/clay nanocomposites possess a higher modulus and greater melt strength than PLA/PHBV blends. The addition of nanoclay also decreased the average cell size and increased the cell density of microcellular PLA/PHBV specimens. As a crystalline nucleating agent, nanoclay significantly improved the crystallinity of PHBV in the blend, thus leading to a relatively high modulus for both solid and microcellular specimens. However, the addition of nanoclay had less of an effect on the tensile strength and strain-at-break.     

Microcellular injection-molding of polylactide with chain-extender

The effects of adding an epoxy-based chain-extender (CE) on the properties of injection-molded solid and microcellular polylactide (PLA) were studied. PLA and PLA with 8 wt.% CE (PLA-CE) were melt-compounded using a twin-screw extruder. Solid and microcellular specimens were produced via a conventional and microcellular injection-molding process, respectively. Various characterization techniques including gel permeation chromatography, tensile testing and dynamic mechanical analysis, scanning electron microscopy and differential scanning calorimetry were applied to study the molecular weight, static and dynamic mechanical properties, cell morphology, and crystallization behavior, respectively. The addition of CE enhanced the molecular weight but decreased the crystallinity of PLA. The addition of CE also reduced the cell size and increased the cell density. Furthermore, the decomposition temperatures and several tensile properties, including specific strength, specific toughness, and strain-at-break of both solid and microcellular PLA specimens, increased with the addition of CE.     

Development of PLA/cellulosic fiber composite foams using injection molding: Crystallization and foaming behaviors

Poly(lactic acid) (PLA) and northern bleached softwood kraft (NBSK) or black spruce medium density fiberboard (MDF) fibers were melt compounded using a co-rotating twin screw extruder and subsequently microcellular injection molded. Poly(ethlylene glycol) (PEG) was used as a lubricant. The microcellular structure, thermal properties, and crystallization behaviors were characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and wide angle X-ray diffraction. Results show that cellulosic fibers, acting as crystal nucleating agents, increased the crystallization temperature and the crystallinity and decreased the crystallization half time. The dissolved N₂, the shear stress, and biaxial stretching during foaming also enhanced the crystallinity of PLA. Compared to PLA/PEG, a finer and more uniform cell structure was achieved in the cellulosic fiber composite foams. The improved foam morphology was attributed to the cell nucleating effects of the fibers and the increased melt strength by the addition of cellulosic fibers and by the gas- and fiber- induced crystallization.     

Microcellular processing of polylactide–hyperbranched polyester–nanoclay composites

The effects of addition of hyperbranched polyesters (HBPs) and nanoclay on the material properties of both solid and microcellular polylactide (PLA) produced via a conventional and microcellular injection-molding process, respectively, were investigated. The effects of two different types of HBPs (i.e., Boltorn H2004^? and Boltorn H20^?) at the same loading level (i.e., 12%), and the same type of HBP at different loading levels (i.e., Boltorn H2004^? at 6 and 12%), as well as the simultaneous addition of 12% Boltorn H2004^? and 2% Cloisite^?30B nanoclay (i.e., HBP–nanoclay) on the thermal and mechanical properties (both static and dynamic), and the cell morphology of the microcellular components were noted. The addition of HBPs and/or HBP with nanoclay decreased the average cell size, and increased the cell density. The stress–strain plots of all the solid and microcellular PLA-H2004 blends showed considerable strain softening and cold drawing, indicating a ductile fracture mode. Among the two HBPs, samples with Boltorn H2004^? showed higher strain-at-break and specific toughness compared to Boltorn H20^?. Moreover, the sample with Boltorn H2004^? and nanoclay exhibited the highest strain-at-break (626% for solid and 406% for microcellular) and specific toughness (405% for solid and 334% for microcellular). Finally, the specific toughness, strain-at-break, and specific strength of microcellular samples were found to be lower than their solid counterparts.     

A novel technology to manufacture biodegradable polylactide bead foam products

Bead foaming technology with double crystal melting peak structure has been recognized as a promising method to produce high-performance low-density foams with complex geometries. Polylactide (PLA) bead foaming has been of the great interest of researchers due to its origin from renewal resources and biodegradability. However, due to the PLA’s low melt strength and slow crystallization kinetics, the attempts have been limited to the manufacturing methods used for expanded polystyrene (EPS). In this study, we developed microcellular PLA bead foams with double crystal melting peak structure in a large content using a lab-scale autoclave system followed by molding of the beads. PLA bead foams were produced with expansion ratios and average cell sizes ranging from 6 to 31-fold and 6 to 50 μm, respectively. The high-melting point crystals generated during gas-saturation significantly affected the expansion ratio and cell density of the PLA bead foams by enhancing the PLA’s melt strength and promoting cell nucleation around the crystals. The tensile properties of the molded EPLA bead foams showed that EPLA bead foams with double crystal melting peak can be a promising substitute not only for EPS but also for expanded polypropylene (EPP) bead foams.     

Characterization of thermoplastic polyurethane/polylactic acid (TPU/PLA) tissue engineering scaffolds fabricated by microcellular injection molding

Polylactic acid (PLA) and thermoplastic polyurethane (TPU) are two kinds of biocompatible and biodegradable polymers that can be used in biomedical applications. PLA has rigid mechanical properties while TPU possesses flexible mechanical properties. Blended TPU/PLA tissue engineering scaffolds at different ratios for tunable properties were fabricated via twin screw extrusion and microcellular injection molding techniques for the first time. Multiple test methods were used to characterize these materials. Fourier transform infrared spectroscopy (FTIR) confirmed the existence of the two components in the blends; differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirmed the immiscibility between the TPU and PLA. Scanning electron microscopy (SEM) images verified that, at the composition ratios studied, PLA was dispersed as spheres or islands inside the TPU matrix and that this phase morphology further influenced the scaffold's microstructure and surface roughness. The blends exhibited a large range of mechanical properties that covered several human tissue requirements. 3T3 fibroblast cell culture showed that the scaffolds supported cell proliferation and migration properly. Most importantly, this study demonstrated the feasibility of mass producing biocompatible PLA/TPU scaffolds with tunable microstructures, surface roughnesses, and mechanical properties that have the potential to be used as artificial scaffolds in multiple tissue engineering applications.     

Microcellular extrusion foaming of poly(lactide)/poly(butylene adipate-co-terephthalate) blends

Foamed poly(lactide) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were processed via the microcellular extrusion process using CO₂ as a blowing agent. Talc has been added to promote heterogeneous nucleation. Two types of PLA/PBAT blend systems were investigated: Ecovio, which is a commercially available compatibilized PLA/PBAT blend; and a non-compatibilized PLA/PBAT blend at the same PLA/PBAT ratio (i.e., 45:55 by weight percent). Six different formulations were investigated: pure PLA, PLA-talc, Ecovio, Ecovio-talc, non-compatibilized PLA/PBAT blend, and non-compatibilized PLA/PBAT-talc. The effects of various processing parameters such as die temperature, talc and compatibilization on various foaming properties such as cell morphology, volume expansion ratio (VER), open cell content (OCC) and crystallinity were investigated. As per the DSC thermograms, it was observed that compatibilization has merged the two distinctive melting peaks of PLA and PBAT into a single peak while lowering the peak temperature. In general, the addition of talc has decreased the average cell size and VER and increased the cell density and crystallinity; however, it has varying effects on the open cell content. Compatibilization has reduced the average cell size and volume expansion but increased the cell density and had varying and no effects on the OCC and crystallinity, respectively. Similar to compatibilization, the die temperature was found to have varying and no effects on the OCC and crystallinity, respectively. Except for PLA and non-compatibilized PLA/PBAT blend, the cell size and VER of all other formulations did not vary much throughout the entire temperature range (130–150 °C). The cell density was found to be insensitive to die temperatures except for Ecovio and Ecovio-talc.     

Processing of microcellular preceramics using carbon dioxide

An innovative processing route for developing microcellular ceramics has been developed. This newly designed technology relies on the implementation of the principle of inducing a thermodynamic instability in the production process for microcellular preceramic polymers that are further transformed into microcellular ceramics using pyrolysis. In this work, we have particularly focused on studying the feasibility of fabricating microcellular ceramics and the processing parameter-cell density relationships in the processing of microcellular preceramic polymers. The presented results indicate that the proposed novel processing method is suitable for the manufacture of porous ceramics with high uniformity of the cell size, shape, and volume.     

Fabrication of cellular and microcellular ceramics with controllable open-cell content from polysiloxane-LDPE blends: I. Compounding and Foaming

A novel processing route for fabricating cellular and microcellular ceramics with controllable open-cell content has been developed. The proposed strategy for producing cellular and microcellular ceramics involves: (i) development of desired foamable polysiloxane–polyolefin blends by using a compounder element, in which the polyolefin phase is uniformly dispersed in the polysiloxane matrix, (ii) foaming the obtained blends by implementing the thermodynamic instability principle to produce a cellular or microcellular ceramic precursor structure, and (iii) completing the organic–inorganic transition without sacrificing the obtained cellular or microcellular structure and inducing open-channels in the cell walls by burning out the sacrificial dispersed polyolefin phase at elevated temperatures. By controlling the viscosity of the dispersed polyolefin phase, the polyolefin concentration and compounding parameters, the polysiloxane–polyolefin blend morphology can be varied. Furthermore, plus a deliberate control of foaming and pyrolyzing parameters, the foam morphology and open-cell content of produced cellular and microcellular ceramics can be adjusted. In this paper, the technique to get a desired cellular and microcellular ceramic precursor structure is demonstrated. The deliberate pyrolysis technique to complete the organic–inorganic transition and the mechanical properties of the obtained microcellular ceramics will be discussed in another paper.