微孔发泡聚乳酸泡孔结构调控及性能研究

发布时间：2018-02-22 05:36

本文关键词： 微孔发泡超临界二氧化碳聚乳酸异相成核二元泡孔　出处：《华南理工大学》2015年博士论文　论文类型：学位论文

【摘要】：超临界流体微孔发泡技术自上世纪八十年代问世以来,得到广泛的研究和发展。随着人们环保意识的提高,发展绿色经济,研究人员已将微孔发泡技术用于注塑、挤出和中空制品的商业化生产。同时将目光集中在对环境污染少、能耗低、可自然降解、来源广泛的高分子材料上。聚乳酸(PLA)由于具有绿色植物来源性和可生物降解性,因而成为研究的一大热点。聚乳酸发泡材料能够取代石油基发泡塑料应用与包装和生活消费品领域。PLA属于半结晶型聚合物,结晶速率慢,耐热性差,熔体强度不高,在发泡过程中容易出现泡孔塌陷合并现象,这些因素不利于发泡。为了全面、深入地研究聚乳酸发泡材料的性能,制备出具有良好泡孔结构形态的PLA发泡材料,即增加泡孔密度、减小泡孔尺寸及均化泡孔分布。本文通过自制的高压釜及模具利用快速卸压的发泡方法制备出PLA微孔材料,首先研究了影响PLA微孔发泡的工艺条件对泡孔形态的影响规律,同时对制得的微孔发泡样品进行力学性能试验以及隔热性能测试,以泡孔微结构为桥梁,建立微孔发泡材料性能与发泡工艺之间的关系。实验结果表明,通过调节发泡压力,平均泡孔尺寸可在6-280μm范围内变化。对比两种牌号的PLA发泡材料发现,PLA4032D由于右旋乳酸含量低,结晶度高,同时分子量较大,熔点以及熔体的粘度要高于PLA2003D,因此在相同发泡条件下,得到的泡孔尺寸要小。发泡材料的压缩强度和压缩屈服应力均随着发泡压力的增加呈现先增大后降低的变化趋势。拉伸强度和断裂伸长率也都随着发泡压力增大呈现先增加而后减小的变化趋势。热导率随着压力增加呈下降趋势,但在高压的时候,热导率反而有所上升。聚乳酸由于CO2气体的增塑作用,其在高压气体下的结晶能力提高,结晶度随着发泡温度的降低而升高,同时形成的球晶结构尺寸更大,规整度更高。这将不利于形成均匀的泡孔结构,气体在大球晶区域中的溶解度下降,出现未发泡区域,但是适当的结晶度却可以提高熔体的强度,减小泡孔尺寸。对力学性能研究发现,存在一个最佳发泡温度,在此温度下压缩强度达到最大值。PLA发泡样品随着发泡空间增大,泡孔取向程度变大,泡孔壁在生长方向拉伸变薄甚至破裂。压缩强度和拉伸模量均随着发泡空间的减少而增大。具有双峰分布的二元泡孔结构微孔塑料综合性能优异,实验通过二步卸压的方法制备出PLA二元泡孔结构,当第一步卸压至中间压力的压力降在2-8 MPa的范围内可以形成二元泡孔结构。压缩性能实验表明:随着第一步卸压至中间压力的压差增加,发泡材料的压缩强度下降。提高发泡温度,大泡孔出现合并或泡孔壁破裂,将不利于二元泡孔的力学性能。实验还对比了三种纳米粒子对PLA结晶性能的影响,其中CNT促进PLA基体结晶能力最强,结晶度较高。在高压饱和气体增塑作用下,PLA/CNT纳米复合材料在80 oC时的结晶度最高,且形成的球晶尺寸较大,规整度高,由于晶区不吸收气体而导致不能发泡。当提高发泡温度至100 oC,晶区结构变得小而均匀,可以引发较小的泡孔尺寸和较大的泡孔密度。进一步提高发泡温度到120 oC时,虽然晶区的异相成核作用依然存在,但是高温时PLA基体的熔体粘度会随之下降,在此温度下泡孔的尺寸稍有增加。本文最后研究了聚乳酸/聚丁二酸丁二醇酯(PLA/PBS)共混体系的发泡性能,通过改变共混组分配比和发泡温度来调控发泡制品的泡孔形态,由于发泡温度接近PBS相熔点,熔点较低的PBS相可以有效的提高泡孔的连通率,当PBS质量分数为20 wt%时,共混体系的开孔率达到最大(96.2%),提出了共混物近熔点发泡开孔机理,并运用到双峰分布结构泡孔制备中,成功制备出开孔率达到96%,孔间高度连通的可生物降解的二元泡孔结构。
[Abstract]:Since the last century since the 80s advent of supercritical fluid foaming technology, obtained extensive research and development. With the improvement of people's environmental awareness, the development of green economy, the researchers have microcellular foaming technology for injection molding, extrusion and commercial production of hollow products. At the same time will focus on less environmental pollution and low energy consumption. Biodegradable polymer materials, sources widely. Polylactic acid (PLA) with green plant sources and biodegradable, and thus become a hot research topic. Plafoam material can replace petroleum based plastic foam application and packaging and consumer goods belonging to the.PLA semi crystalline polymer, slow crystallization rate, poor heat resistance, melt strength is not high, easy to appear in the foaming process with foam collapse phenomenon, these factors are not conducive to foaming. In order to comprehensive, in-depth research of plafoam The properties of materials, prepared with PLA foam material good pore structure morphology, namely increased cell density, smaller cell size and average pore distribution. By using self-made autoclave and mould foaming method rapid pressure relief by PLA microporous materials, firstly studied the influence law of bubble effects of process conditions on the morphology of PLA microcellular foam, while the mechanical properties test and insulation performance test of microcellular foam samples, with pore micro structure as a bridge to establish the relationship between microcellular material properties and foaming process. The experimental results show that, by adjusting the foaming pressure, the average pore size can be changed in the 6-280 m range. PLA foaming material comparison of two kinds of PLA4032D because of D-lactic acid content is low, high crystallinity, and large molecular weight, melting point and viscosity of the melt is higher than that of PLA2003D, so in Under the same foaming conditions, the cell size is smaller. The foam compressive strength and yield stress increased with the trend of increased first and then decreased with increasing foaming pressure. The tensile strength and elongation are increased with the foaming pressure first increase and then decrease the thermal conductivity. With the increase of pressure a downward trend, but in the pressure when the thermal conductivity increased. Polylactic acid CO2 gas due to the plasticizing effect, improve the crystallization ability under high pressure gas, the crystallinity decreased with the increase of foaming temperature, spherulite structure size with the formation of larger, higher regularity. This will not conducive to the formation of uniform pore structure, decrease the gas solubility in the spherulite region, not foaming area, but proper crystallinity can improve melt strength, reduce the cell size on the mechanical properties of force. The study found that there is an optimum foaming temperature, this temperature compression strength reaches the maximum value of.PLA foam samples with foam space increases, the bubble orientation degree becomes larger, the cell wall in the growth direction stretched thin and even rupture. The compressive strength and tensile modulus increased with the decrease of foaming space increases with the distribution of Shuangfeng. Two yuan bubble pore structure of Microcellular Plastics excellent comprehensive performance, through the experiment of two step method of unloading prepared PLA two porous structure, when the first step pressure relief to the intermediate pressure in the range of 2-8 MPa can form two yuan pore structure. The compression experiment indicates that: as the first step of unloading the pressure to the middle pressure differential pressure increase, decrease the compressive strength of the foam. Improve the foaming temperature, bubble holes appear merged or cell wall rupture, two yuan will be detrimental to the mechanical properties of foam. The experiment also compared the three kinds of nanoparticles Influence of the crystallization of PLA, of which CNT promotes PLA matrix crystallization ability is the strongest, high degree of crystallinity. Plasticization in high pressure gas saturation, the highest degree of crystallization of PLA/CNT nano composite materials at 80 oC, and the formation of the spherulite size larger, warping degree is high, because the crystal area does not absorb gas to foam when. Improve the foaming temperature to 100 oC, crystal structure becomes small and uniform, can lead to smaller cell size and larger cell density. To further improve the foaming temperature to 120 oC, while the crystalline nucleation still exists, but the high temperature melt viscosity of PLA matrix decreases, at this temperature. The bubble size increases slightly. Finally the polylactic acid / poly butylene succinate (PLA/PBS) foaming properties of the blend system, by changing the blending proportion and foaming temperature to regulate the cell morphology of foamed products, The foaming temperature is close to the PBS phase with low melting point, melting point, PBS can effectively improve the connectivity of the bubble, when the mass fraction of PBS is 20 wt%, the maximum opening rate of the blends (96.2%), the blend hole near the melting point of foaming mechanism, and applied to the Shuangfeng global distribution structure the hole in the preparation of prepared hole rate reached 96%, a high degree of connectivity between hole biodegradable foam structure of two yuan.

【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ328.0

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