本文關(guān)鍵詞： 微孔發(fā)泡 超臨界二氧化碳 聚乳酸 異相成核 二元泡孔　出處：《華南理工大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：超臨界流體微孔發(fā)泡技術(shù)自上世紀(jì)八十年代問世以來,得到廣泛的研究和發(fā)展。隨著人們環(huán)保意識(shí)的提高,發(fā)展綠色經(jīng)濟(jì),研究人員已將微孔發(fā)泡技術(shù)用于注塑、擠出和中空制品的商業(yè)化生產(chǎn)。同時(shí)將目光集中在對(duì)環(huán)境污染少、能耗低、可自然降解、來源廣泛的高分子材料上。聚乳酸(PLA)由于具有綠色植物來源性和可生物降解性,因而成為研究的一大熱點(diǎn)。聚乳酸發(fā)泡材料能夠取代石油基發(fā)泡塑料應(yīng)用與包裝和生活消費(fèi)品領(lǐng)域。PLA屬于半結(jié)晶型聚合物,結(jié)晶速率慢,耐熱性差,熔體強(qiáng)度不高,在發(fā)泡過程中容易出現(xiàn)泡孔塌陷合并現(xiàn)象,這些因素不利于發(fā)泡。為了全面、深入地研究聚乳酸發(fā)泡材料的性能,制備出具有良好泡孔結(jié)構(gòu)形態(tài)的PLA發(fā)泡材料,即增加泡孔密度、減小泡孔尺寸及均化泡孔分布。本文通過自制的高壓釜及模具利用快速卸壓的發(fā)泡方法制備出PLA微孔材料,首先研究了影響PLA微孔發(fā)泡的工藝條件對(duì)泡孔形態(tài)的影響規(guī)律,同時(shí)對(duì)制得的微孔發(fā)泡樣品進(jìn)行力學(xué)性能試驗(yàn)以及隔熱性能測(cè)試,以泡孔微結(jié)構(gòu)為橋梁,建立微孔發(fā)泡材料性能與發(fā)泡工藝之間的關(guān)系。實(shí)驗(yàn)結(jié)果表明,通過調(diào)節(jié)發(fā)泡壓力,平均泡孔尺寸可在6-280μm范圍內(nèi)變化。對(duì)比兩種牌號(hào)的PLA發(fā)泡材料發(fā)現(xiàn),PLA4032D由于右旋乳酸含量低,結(jié)晶度高,同時(shí)分子量較大,熔點(diǎn)以及熔體的粘度要高于PLA2003D,因此在相同發(fā)泡條件下,得到的泡孔尺寸要小。發(fā)泡材料的壓縮強(qiáng)度和壓縮屈服應(yīng)力均隨著發(fā)泡壓力的增加呈現(xiàn)先增大后降低的變化趨勢(shì)。拉伸強(qiáng)度和斷裂伸長(zhǎng)率也都隨著發(fā)泡壓力增大呈現(xiàn)先增加而后減小的變化趨勢(shì)。熱導(dǎo)率隨著壓力增加呈下降趨勢(shì),但在高壓的時(shí)候,熱導(dǎo)率反而有所上升。聚乳酸由于CO2氣體的增塑作用,其在高壓氣體下的結(jié)晶能力提高,結(jié)晶度隨著發(fā)泡溫度的降低而升高,同時(shí)形成的球晶結(jié)構(gòu)尺寸更大,規(guī)整度更高。這將不利于形成均勻的泡孔結(jié)構(gòu),氣體在大球晶區(qū)域中的溶解度下降,出現(xiàn)未發(fā)泡區(qū)域,但是適當(dāng)?shù)慕Y(jié)晶度卻可以提高熔體的強(qiáng)度,減小泡孔尺寸。對(duì)力學(xué)性能研究發(fā)現(xiàn),存在一個(gè)最佳發(fā)泡溫度,在此溫度下壓縮強(qiáng)度達(dá)到最大值。PLA發(fā)泡樣品隨著發(fā)泡空間增大,泡孔取向程度變大,泡孔壁在生長(zhǎng)方向拉伸變薄甚至破裂。壓縮強(qiáng)度和拉伸模量均隨著發(fā)泡空間的減少而增大。具有雙峰分布的二元泡孔結(jié)構(gòu)微孔塑料綜合性能優(yōu)異,實(shí)驗(yàn)通過二步卸壓的方法制備出PLA二元泡孔結(jié)構(gòu),當(dāng)?shù)谝徊叫秹褐林虚g壓力的壓力降在2-8 MPa的范圍內(nèi)可以形成二元泡孔結(jié)構(gòu)。壓縮性能實(shí)驗(yàn)表明:隨著第一步卸壓至中間壓力的壓差增加,發(fā)泡材料的壓縮強(qiáng)度下降。提高發(fā)泡溫度,大泡孔出現(xiàn)合并或泡孔壁破裂,將不利于二元泡孔的力學(xué)性能。實(shí)驗(yàn)還對(duì)比了三種納米粒子對(duì)PLA結(jié)晶性能的影響,其中CNT促進(jìn)PLA基體結(jié)晶能力最強(qiáng),結(jié)晶度較高。在高壓飽和氣體增塑作用下,PLA/CNT納米復(fù)合材料在80 oC時(shí)的結(jié)晶度最高,且形成的球晶尺寸較大,規(guī)整度高,由于晶區(qū)不吸收氣體而導(dǎo)致不能發(fā)泡。當(dāng)提高發(fā)泡溫度至100 oC,晶區(qū)結(jié)構(gòu)變得小而均勻,可以引發(fā)較小的泡孔尺寸和較大的泡孔密度。進(jìn)一步提高發(fā)泡溫度到120 oC時(shí),雖然晶區(qū)的異相成核作用依然存在,但是高溫時(shí)PLA基體的熔體粘度會(huì)隨之下降,在此溫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)共混體系的發(fā)泡性能,通過改變共混組分配比和發(fā)泡溫度來調(diào)控發(fā)泡制品的泡孔形態(tài),由于發(fā)泡溫度接近PBS相熔點(diǎn),熔點(diǎn)較低的PBS相可以有效的提高泡孔的連通率,當(dāng)PBS質(zhì)量分?jǐn)?shù)為20 wt%時(shí),共混體系的開孔率達(dá)到最大(96.2%),提出了共混物近熔點(diǎn)發(fā)泡開孔機(jī)理,并運(yùn)用到雙峰分布結(jié)構(gòu)泡孔制備中,成功制備出開孔率達(dá)到96%,孔間高度連通的可生物降解的二元泡孔結(jié)構(gòu)。
[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.

【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ328.0

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本文編號(hào)：1523755