【作者】 彭军；

【导师】 彭响方；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2011， 博士

【摘要】 微孔发泡注射成型技术是近年发展起来的一种新型聚合物成型加工方法,此种法可以降低加工温度、降低注射压力、减小对锁模力、缩短成型周期和节约能耗。微孔气泡在制品内部均匀分布,泡孔的内压可以抵抗塑料制品成型过程中的冷却收缩,使制品具有尺寸稳定性好及质量轻的特点。然而,这项技术也存在一些限制,最突出的是微孔发泡注射成型制品的表面质量不够好,经常伴有气穴和银纹等表面缺陷。当制品对外观有严格要求时,微孔发泡注射成型技术的应用就受到限制。因此,如何改善微孔发泡注射成型制品的表面质量对于微孔发泡注射成型技术的发展具有重要意义。进而如何在促进微孔发泡注射成型技术发展的同时,可以降低设备成本和简化流程,并且从根本上解决微孔制品表面质量不好的难题,对微孔发泡注射成型技术提出新的挑战。不仅如此,在对微孔发泡注射成型技术研究的基础上,促进其在其他领域,特别是在医疗领域的应用,为微孔发泡注射成型技术指出新的发展方向。本课题系统的研究了应用滑移作用和应用可膨胀热塑性微球(ETM)做为发泡剂的两种方法对改善微孔发泡注射成型制品表面质量的作用。研究发现,应用滑移作用,通过在聚合物基体中添加外润滑剂可以有效增强滑移作用,从而改善发泡制品的表面质量。定义滑移速度定量表征滑移作用,滑移速度是外润滑剂添加量和加工参数(注射速度、模具温度)的函数。第二种方法,应用可膨胀热塑性微球(ETM)做为发泡剂提高微孔发泡注射成型制品的表面质量。应用ETM做为发泡剂,在常规注射机上实现制备微孔塑料制品,由于微球本身的皮层结构能够限制气体的溢出而使微孔制品具有较好的表面形态。实验结果表明应用滑移作用和应用ETM做为发泡剂的方法可以有效的降低微孔发泡注射成型制品的表面粗糙度。随着微孔发泡注射成型技术的发展,现在的研究热点和难点集中于如何在保持微孔塑料众多优点的基础上,可以节约设备成本和原材料成本,同时还可以改善微孔制品的表面质量。本文研制成功以水做为发泡剂的新型微孔发泡注射成型技术,并且在自行搭建的实验平台上实现制备微孔发泡注射成型聚碳酸酯制品。在制品重量降低10%时,以水做为发泡剂的微孔制品(如聚碳酸酯)比以超临界流体作为发泡剂的制品具有更好的表面质量,几乎媲美于固体注射制品。新型微孔发泡注射成型技术:把盐水泵入到料筒中,水作为物理发泡剂,重结晶的盐粒子(10~20微米)作为成核剂。此过程不需要复杂的超临界流体控制单元和注气单元,从而大幅度节约设备成本。本论文不仅深入探讨微孔发泡注射成型技术本身,还进一步研究了微孔发泡注射成型技术的应用,特别是在制备组织工程多孔支架领域的应用。在微孔发泡注射成型混合物制品中,由于不同聚合物之间的互补作用而表现出不同于单相聚合物制品的性能。本文对比研究了固体和微孔发泡注射成型聚(己二酸丁二酯-对苯二甲酸丁二酯) (PBAT)/聚乙烯醇(PVA)混合物及聚乳酸(PLA)/聚乙烯醇(PVA)混合物两相体系的热性能,流变性能,机械性能,两相体系的微观形态和泡孔的微观结构。在对微孔发泡注射成型可降解两相系混合物研究的基础上,制备出具有多孔性通孔的PLA支架。更多还原

【Abstract】 Microcellular injection molding enable to fabricate microcellular plastic parts by low temperatures and pressures leading to a reduction of clamp tonnage required, cycle time, and energy consumption. In addition, the expansion of the gas inside of the polymer melt creates a uniform packing effect and prevents the material from shrinking during cooling, leading to excellent dimensional stability of molded parts. However, the benefits of this technology also come with some limitations, notably a surface finish with swirls and silver streaks resulting from the stretching and collapsing of bubbles on the foamed part surfaces. For applications with strict part appearance requirements, the surface swirl marks on the molded part limit the adoption of microcellular injection molding unless the surface quality can be improved with other techniques.To improve surface roughness and maintain mechanical properties, two methods in this thesis were employed to achieve a better surface quality of microcellular injection molded products. Slip effects enhanced by external lubricant additives is capable to improve the surface qualities of microcellular foamed parts. Additionally, expandable thermoplastic microspheres (ETM) based on conventional injection molding can fabricate microcellular plastic parts with smooth surface qualities.The urgent requirements for microcellular injection molding technique focus on how to further save the cost and simultaneously obtain the smooth surface of foamed parts as well as conventional benefits. A novel microcellular injection molding technique using water as a blowing agent, the technique is capable to fabricate polycarbonate (PC) microcellular injection molded parts with good surface qualities and mechanical properties. The new process for produce microcellular injection molded plastics parts using water as the physical blowing agent and micro-scaled salt particles as the cell nucleating agents. 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 smoother 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. In comparison with single polymer microcellular injection molded parts, two-phase blends as foamed matrices have more benefits to improve the mechanical properties, thermal properties and cell morphologies based on complementary interaction. The properties of solid and microcellular injection molded biodegradable polylactic acid (PLA)/polyvinyl alcohol (PVA) blends and Poly (butylenes adipate-co-terephthalate) (PBAT)/polyvinyl alcohol (PVA) blends are investigated in terms of rheology properties, thermal properties, mechanical properties, morphologies, nucleating rate, and cell microstructures with various compositions ratios. Moreover, targeted for potential medical applications and tissue engineering scaffold applications, microcellular injection molding technique is probably employed to fabricate highly porous biodegradable polymer scaffold. Porous PLA matrices are fabricated for potential application of scaffolds.更多还原