【作者】 原伟杰；

【导师】 岳永德；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2014， 博士

【摘要】 聚乳酸，又称聚丙交酯，因原材料易获取，可完全降解，无害性等特点，在减少环境污染、节省石油资源及减轻地球温室效应方面具有重要的应用意义，因而被认为是最具发展前景的理想绿色高分子材料之一。聚乳酸已被引入到我国的荒漠化防治领域并且取得了理想的防沙固沙效果，目前主要的利用途径是铺设聚乳酸沙障。本研究通过在乌兰布和沙漠及毛乌素沙地铺设不同规格的聚乳酸沙障，测定沙障不同铺设时间及铺设位置下的物理、化学性能、热性能及表面形貌变化，解析了聚乳酸沙障的降解老化过程，揭示了影响聚乳酸沙障降解老化的主要因素。通过对比其他常见高分子纤维材料沙障在沙区应用的老化情况，评价了聚乳酸沙障的耐久性。针对聚乳酸沙障在沙区应用过程中出现的漏沙现象，提出了解决办法并进行了验证。主要结论如下：（1）聚乳酸沙障织物的顶破强力损失率、失重率和单纱断裂强度损失率均随着铺设时间的延长而增大，至5a时，三者的平均值分别为44.1%，22.21%，70.53%，变化速度并不一致。（2）单根聚乳酸沙障障体上下左右4个不同部位的沙障降解老化程度由高到低依次为：障体迎风面、障体顶部、障体背风面、障体贴地面，且四者之间的差异性随时间增加逐渐减小。说明风沙活动对聚乳酸沙障的降解老化起着最重要的作用，其次是光照和水分影响，且随时间增加，这些环境因素之间的影响力差异逐渐减小。（3）乌兰布和沙漠沙障障体暴露面的降解程度高于贴地面部分，且二者差异较大。而毛乌素沙地沙障障体暴露面与贴地面的降解程度之间差异较小，表明不同研究区域下风沙活动、光照及土壤水分等环境因素作用强度不一。生长季0.5-1a（5月-10月）的聚乳酸沙障降解程度较非生长季0.5-2a（11月-翌年4月）的稍大，表明不同取样时间下风沙活动、光照及土壤水分的差异对于聚乳酸沙障降解老化性能有重要的影响。（4）FT-IR分析显示聚乳酸沙障在前5a的整个降解老化过程中并无新旧官能团的产生及消失，表明其在沙区的应用性能较为稳定。到铺设5a时聚乳酸沙障的—CH发生明显振动，表明长时间的光照是影响聚乳酸沙障的主要因素之一；聚乳酸沙障相对分子量随时间增加逐步降低，分子量分布宽度逐渐变大，变化幅度分别为33.96%、6.63%，说明聚乳酸大分子逐渐降解为小分子。通过建立一级动力学模型方程预测聚乳酸沙障的使用寿命半衰期约为8.5a。（5）随着铺设时间的延长，聚乳酸沙障的玻璃化转变温度先上升后下降，同时，熔点下降，熔融焓增大，结晶度增大，表明聚乳酸沙障随铺设时间的延长降解老化程度不断加深，但仍处于无定型区降解阶段。（6）随铺设时间的延长，聚乳酸沙障障体的纱线结构由较为完整到开始出现凌乱和部分破坏，而纤维表面则由团簇状碎片、条状及片状剥皮逐渐发展至凹槽块状纤维脱落、开裂。初步判断聚乳酸沙障的降解老化尚处于初期至中期阶段，远未达到最终使用寿命。试验地同期铺设2a后，聚乳酸沙障的顶破强力损失率仅为25.06%，7种常规化纤材料沙障中顶破强力损失率最小的是47.68%，最大的已经达到100%。表明聚乳酸沙障具有比其他常规化纤材料沙障优越的耐降解老化性能，适宜在沙区推广使用。（7）不同铺设规格的聚乳酸沙障在降解老化过程中无明显差异。由于沙丘不同部位的风沙活动、光照、土壤水分含量等环境因素分布的差异而导致相应部位的聚乳酸纤维沙障降解程度不同，降解老化程度呈如下规律：沙丘顶部＞迎风坡坡中＞迎风坡坡底＞背风坡坡底＞背风坡坡中；迎风坡不同坡位的沙障整体降解老化程度比背风坡的偏大。不同沙埋深度的聚乳酸沙障降解老化程度随土壤含水率的变化表现为先增大后降低，且随沙埋时间的增加，不同埋深处的聚乳酸沙障降解老化程度差异越来越大。表明土壤水分是影响聚乳酸沙障降解老化的一个重要因素。（8）100℃沸水加热处理1.5min能显著增大聚乳酸沙障织物密度，减小织物孔径大小，使纵向长度为5cm的沙障织物的线圈数达到93个，明显改善漏沙情况，减少漏沙量为78.5%，对其本身的化学性能、热性能及表面形貌没有任何影响。但沙障织物纵向长度显著减小，单丝细度稍有下降，而横向宽度及重量变化不大。更多还原

【Abstract】 The Polylactic Acid（PLA）has many advantages, such as easily available raw materials,good physical and chemical properties, complete biodegradable and harmless, which make ithas important significance in reducing environmental pollution, saving oil resources andreducing greenhouse gas effect. The PLA is becoming one of the most prospective greenenvironmental protection materials. The PLA materials have been introduced into the area ofdesertification combating, and achieved promising effects on desertification prevention andtreatment.Various patterns of the PLA sand barriers were laid on the dune of Ulanbuh desert and MuUs sandland and regularly sampled. The change of physical, chemical, thermal properties andsurface morphology of different part of PLA sand barriers with the increased laying time weremeasured, the process and laws and the main impact factors of the degradation of PLA sandbarriers were analyzed and revealed. Combined with laboratory simulation and field test, thepolish resistance properties of PLA sand barriers were evaluated and the empirical evaluationequation was established. The improvement measures for the sand leakage in the application ofPLA sand barriers were proposed and verified. The main conclusions are as follows:（1）The loss ratio of bursting strength,single yarn breaking strength and weight increasedwith the laying time, and reached to48.28%,78.77%and23.05%after5years, respectively.Their variation speed were inconformity.（2）The degradation degree of different part of the barrier body ranked in the descendingorder as windward part, top part, leeward part and the ground part. The difference of thedegradation degree for4parts of barrier body decreased with the increase of laying time, whichindicated that the wind-sand activity was the most important impact factor for the degradationof PLA sand barriers, following as light and soil water, the impact of environmental factorsdecreased with the increase of time. （3）The degradation degree of the exposed part of sand barriers was higher than theground part in Ulan buh desert, and the difference was significant. While the difference of thedegradation degree between the two parts in Mu Us Sandland was small, which indicated thatthe impact intensity of the wind-sand activity and light and soil water varied in different studyarea. The degradation degree of PLA sand barriers in growing season (May to October) andnon-growing season (November to following March) half year were different, and thedegradation degree in in growing season was higher than in non-growing season, whichindicated that the environment difference such as the wind-sand activity and light and soilwater between the sampling time impacted the degradation degree of sandbag barriers（4）The FT-IR analysis showed that there were no generation and disappear of new or oldfunctional groups, which indicated that the PLA sandbag barriers were stable in the sand area.The results of FTIR analysis showed that the–CH vibrated significantly, which indicated thatthe long time exposure to the light was one of the important factors that impact the degradationof PLA. The measurement of relative molecular weight showed that the relative molecularweight of PLA sand barriers decreased with the increase of time, the average value haddecreased33.96%. The distribution of relative molecular weight was becoming wider, theaverage value had decreased6.63%.which means that the degradation degree of PLA wasaggravating. The half life of the PLA sand barriers’ service life was predicted to be about8.5athrough the establishment of first order kinetics model.（5）The DSC thermal analysis results showed that with the extension of time, the glasstransition temperature of the PLA sand barriers first increased then decreased. Meanwhile, themelting point decreased, the melting enthalpy and crystallinity increased. All these indicatedthe degradation degree of PLA sand barriers was increasing with the extention of laying time,but it was still in the amorphous zone degradation stage.（6）The results of scanning electron microscope showed that the structures of barriers’yarns were destroyed with the extension of time. The demolishment of fiber surfacetransformed from strip peeling off to groove block off even to crack. It can be estimated that the PLA sand barriers were in the initial stage and medium stage of degradation. Theaccelerated degradation stage did not reached. The bursting strength loss rate of PLA sandbarriers was25.06%after being laid2years, while the bursting strength loss rate of7conventional chemical fiber materials varied from47.68%to100%, which indicates that thePLA sand barriers has the advantages of degradation resistence and they are suitable for beingwidely used in the sandy area（7）Due to the comprehensive effect of environmental factors, the degradation degrees ofthe PLA sandbarriers distributed on the different part of dune were different. The sand barrierslocated on the top of dunes and in the middle part of windward slope suffered the severestdegradation, followed as the bottom parts of windward and leeward slope, the middle part ofthe leeward slope suffered the least severe degradation. All the sand barriers laid on thewindward side suffered severer degradation than that laid on the leeward side.Overall, thedegradation degrees of the sand barriers distributed on different part of windward slope wereseverer than that of on leeward slope. There are no obvious differences in the degradationprocess of PLA sand barriers among different laying patterns. The experiment of sand bury inthe lowland showed that the degradation degrees varied with the difference of water content,the difference was becoming larger with the increase of burying time, which indicated that thesoil water content was an important factor that affects the PLA sand barriers degradation.（8）Boiled for1.5min in the100℃water, the fabric density of PLA sand barrierssignificantly increased, meanwhile the pore diameter of the fabric reduced significantly.Thenumber of coils reached93per5cm after boiling. The situation of the sand leakage of PLAsand barriers improved significantly, and the leakage amount of sand reached78.5%. Theimpact on the chemical and thermal properties and surface morphology was little. Whereas thelength of the fabric significantly reduced, the fineness of single yarn decreased slightly, so didthe width and the weight of fabric.更多还原