聚乳酸自然降解性能

通过注射成型工艺制备聚乳酸(PLA)标准试件,研究了聚乳酸标准试件自然降解性能。结果表明,PLA试件埋于土壤中后逐步分层缓慢降解,复合材料质量逐渐减少;PLA分子链上酯基与水反应,分子链不断断裂,结晶度减小,平均分子量降低,分子量分布变窄,其拉伸强度和冲击强度逐渐下降。12个月后,PLA试件质量损失率仅达到0.23%,PLA重均分子量降低了15.3%,PLA试件的冲击强度和拉伸强度分别降低了17.4%和17.2%。总体而言,PLA在土壤中的自然降解效率较低。     

竹纤维增强聚乳酸复合材料热老化性能

采用氢氧化钠和异氰酸酯处理的界面调控方法对竹纤维(BF)增强聚乳酸(PLA)复合材料界面进行调控,通过注射成型工艺制备BF/PLA复合材料。利用FTIR、XRD、凝胶渗透色谱及SEM等分析手段研究了BF/PLA复合材料热老化性能。研究发现: 热老化过程中PLA分子链中的C O不断水解,分子链的C—O断裂生成聚合度更低的小分子量的PLA,PLA结晶度减小,PLA与BF的接合界面被破坏,拉伸强度和冲击强度随老化时间的增加逐渐降低。BF/PLA复合材料在80℃热老化16天后拉伸强度和冲击强度分别降低了75%和77.6%,在100℃热老化32 h后拉伸强度和冲击强度分别降低了80.3%和83.4%。温度对BF/PLA复合材料老化影响显著,温度越高,老化速度越快。     

竹纤维和海藻酸钠提升聚乳酸的降解性能

为提高聚乳酸(PLA)的降解性，将竹纤维(BF)和海藻酸钠(SA)与PLA共混制备复合材料，并进行土壤降解试验以探究其降解性能，检测降解后复合材料的质量损失率、表面微观结构、官能团变化、热性能和结晶度等指标。结果表明：SA和BF均可提升PLA复合材料降解的质量损失率。降解21天后，BF/PLA和SA-BF/PLA复合材料的质量损失率分别为0.83%和2.54%，相较于纯PLA的0.11%分别提高了7.55和23.09倍。降解后，SA-BF/PLA复合材料的表面出现大量的裂痕与凹陷，这增大了复合材料与土壤中的接触面积，进而加速了复合材料的降解。纯PLA在降解过程中质量损失率很低，但降解后其羰基含量明显上升，表明土壤降解会导致部分PLA长链高分子断裂为小分子。相比于纯PLA,BF/PLA和SA-BF/PLA复合材料的结晶度大幅度降低，表明SA和BF可降低PLA复合材料的结晶度，提高其降解性。由此可见，SA和BF可提升PLA复合材料的降解性能。此研究结果将为高降解性PLA复合材料的制备提供理论参考。     

玄武岩纤维含量对玄武岩纤维/聚乳酸-铝合金复合材料连接强度的影响

为了提高聚乳酸（PLA）与铝合金的连接强度,采用在PLA中添加玄武岩纤维（BF）获得BF/PLA复合材料的方式对PLA进行增强。利用转矩流变仪对干燥处理后的PLA及BF进行密炼,利用光纤激光器对铝合金表面进行毛化处理。采用平板硫化机对BF/PLA复合材料和处理后铝合金进行连接成型,测试其拉伸强度,对失效后断面进行分析。结果表明:随着BF质量分数的增加,BF/PLA-铝合金连接强度先增强后降低,BF质量分数的增加影响了BF/PLA复合材料的结晶成核。结合试验获得的结果,建立有限元分析模型进行数值模拟,结果显示所建立的模型能够准确还原BF/PLA-铝合金拉伸过程。      

蔗渣纤维表面处理方法对蔗渣纤维/聚乳酸复合材料力学性能的影响

采用了硅烷偶联剂结合碱溶液处理的方法对蔗渣纤维(BF)进行了表面改性, 研究了不同表面处理方法对蔗渣纤维/聚乳酸(PLA)复合材料力学性能的影响, 用SEM对BF处理前后的形貌及复合材料的冲击断面进行了观察。结果表明: 经表面改性的BF都不同程度地改善了BF与PLA基体之间的界面相容性, 其中碱处理后再经偶联剂处理的方法效果最佳, 在40%(质量分数)蔗渣纤维的高填充量下, 复合材料的拉伸强度和冲击强度分别为纯PLA的85.42%和59.74%, 较好地保持了基体PLA的力学强度; 碱处理使BF表面变粗糙、 长径比增大、 比表面积增加, 与PLA的界面粘结加强, 从而有效地提高了BF/PLA复合材料的力学性能。     

生物降解聚酯弹性体粒子改性聚乳酸复合材料的制备及性能

以不同粒径的羧基封端生物降解聚酯弹性体粒子(CBEP)改性聚乳酸(PLA)制备了CBEP/PLA复合材料,对复合材料的力学、结晶与降解等性能进行了测试,并研究了CBEP对PLA性能的影响及作用机理。结果表明,CBEP可显著提高PLA的韧性,复合材料样条在拉伸时出现了颈缩现象,尤其是添加了7.5% (与PLA的质量比)粒径在200 nm的CBEP-a的复合材料的断裂伸长率由纯PLA的4.6%提高至155%,而复合材料的缺口冲击强度最高达到了纯PLA的2倍。同时CBEP可提高PLA的结晶性能,其中添加7.5%粒径在200 nm的CBEP-a的复合材料的等温结晶半结晶时间较纯PLA缩短了21.4%。而降解实验结果表明,添加了10%粒径在200 nm的CBEP-a的复合材料在脂肪酶环境下与土壤掩埋环境下的降解质量损失率分别由纯PLA的0.34%与0.25%,提高至2.52%与1.20%。CBEP/PLA复合材料在生物医药与环保材料等领域具有广阔的发展与应用前景。      

抗氧剂/光稳定剂对3D打印光致变色木塑复合材料性能的影响

功能性光致变色木塑复合材料(PWPC)使用寿命通常较短,因此本研究将抗氧剂1010和光稳定剂770引入到PWPC中,以改善复合材料的力学和耐光疲劳等性能。采用熔融共混法制得杨木粉/聚乳酸(WF/PLA)基光致变色复合材料,通过熔融沉积技术(FDM)打印成型,对制备的WF/PLA复合材料力学、界面相容性、热稳定性和耐光疲劳性能进行分析表征。与WF/PLA复合材料相比,当只添加抗氧剂1010时,WF/PLA复合材料拉伸、弯曲和冲击强度分别提高了42.58%、23.25%、6.52%;只添加光稳定剂770时,WF/PLA复合材料拉伸强度提高,弯曲强度和冲击强度均下降。当抗氧剂1010与光稳定剂770以质量比为1∶1添加到WF/PLA复合材料中时,在这两种助剂的协同作用下,WF/PLA复合材料的拉伸强度提高了1.8%,弯曲和冲击强度分别减小了9.3%和22.1%,相比于其他复配体系样品,力学性能降低幅度最低。此外,与WF/PLA复合材料相比,抗氧剂1010与光稳定剂770质量比为1∶1的WF/PLA复合材料的热降解性能和耐光变疲劳性能得到改善,质量损失为5%时的温度为219.84℃。老化第10天,其表面颜色变化值ΔE由5.3增至6.7,增加了26.7%。      

碳纤维/聚乳酸复合材料的结晶性能和流变特性

以碳纤维（CF）作填料,制备了CF/聚乳酸（CF/PLA）复合材料,CF的质量比（CF∶PLA）为1%、3%、5%、10%和15%。研究了PLA及CF/PLA复合材料的结晶性能和流变特性。结果表明,质量比≤3%时,CF在基体中起到了异相成核的作用,提高了PLA的结晶性能,XRD衍射峰强度增强,CF/PLA复合材料结晶温度和结晶度分别提高到112.5℃和30.7%,流变特性与纯PLA相似。CF的质量比增加到5%时,达到"渗流阈值",黏度激增,限制了分子链段的自由运动,导致CF/PLA复合材料结晶性能下降。CF质量比为15%时,CF/PLA复合材料结晶温度降低至93.1℃,结晶度只有2.5%。     

增容纳米纤维素/聚乳酸复合材料的制备与性能

采用接枝共聚法制备了马来酸酐和丙烯酸丁酯双单体接枝聚乳酸（PLA）共聚物（mPLA）,然后以mPLA为增容剂,通过溶液浇铸法制备纳米纤维素（NCC）/PLA复合材料。采用SEM、DSC、TG、广角X射线衍射（WXRD）、力学和降解性能测试研究了mPLA对NCC/PLA复合材料的结构和性能的影响。结果表明:mPLA在PLA与NCC之间起到了良好的界面增容作用,促进了NCC在PLA基体中的分散。更精细分散的NCC促进了PLA的结晶成核,复合材料的结晶温度降低,结晶度提高;NCC/mPLA/PLA复合材料的力学性能随着mPLA含量增加呈先上升后下降的趋势,当mPLA含量为8%时,复合材料的拉伸强度和弹性模量与未添加mPLA的复合材料相比,分别提高了30.2%和41.4%;亲水性的NCC加速了NCC/PLA复合材料的降解,加入mPLA后,复合材料的降解速率有所减慢,但仍然快于纯PLA的降解。      

甘蔗渣的改性方法对甘蔗渣/聚乳酸复合材料结构与性能的影响

采用碱处理、硅烷偶联剂及碱处理后再硅烷偶联剂等方法改性甘蔗渣（BF）,将改性后的BF与聚乳酸（PLA）共混制备BF/PLA复合材料。采用TGA、FTIR和SEM分析研究BF/PLA复合材料的热稳定性;分别采用Flynn-Wall-Ozawa（FWO）法和Kissinger法研究BF/PLA复合材料的热分解动力学。结果表明,BF/PLA复合材料的热稳定与BF的结构及BF/PLA复合材料的界面相容性有关。碱处理使BF原纤化,降低BF的耐热性,不利于BF/PLA复合材料热稳定性及力学性能的提高;硅烷偶联剂改性可以改善BF与PLA的界面相容性,有助于提高BF/PLA复合材料的热稳定性。FWO法与Kissinger法计算得到的热分解活化能较一致,说明这两种方法都适合研究BF/PLA复合材料的热分解动力学。在所对比的BF/PLA复合体系中,硅烷偶联剂改性的BF/PLA复合材料热分解活化能最高、力学性能最佳,碱处理后再硅烷偶联剂改性的BF/PLA复合材料次之。     

Influence of chemical surface modification on the properties of biodegradable jute fabrics—polyester amide composites

The chemical surface modifications of jute fabrics involving bleaching, dewaxing, alkali treatment, cyanoethylation and vinyl grafting are made in view of their use as reinforcing agents in composites based on a biodegradable polyester amide matrix, BAK 1095. The effect of different fibre surface treatments and fabric amounts on the performance of resulting composites are investigated. The mechanical properties of composites like tensile and bending strengths increase as a result of surface modification. Among all modifications, alkali treatment and cyanoethylation result in improved properties of the composites. The tensile strength of BAK is increased by more than 40% as a result of reinforcement with alkali treated jute fabrics. SEM investigations show that the surface modifications improve the fibre–matrix interaction. From degradation studies we find that after 15 days of compost burial about 6% weight loss is observed for BAK whereas cyanoethylated and alkali treated jute–BAK composites show about 10% weight loss. The loss of weight as well as the decrease of bending strength of degraded composites is more or less directly related.     

In vitro predegradation at elevated temperatures of poly(lactide)

In this study in vitro predegradation at elevated temperatures, used to obtain an increased degradation rate, was investigated. The in vitro degradation was followed by mass loss, molecular weight loss and changes in thermal properties. Two biodegradable polymers, the homopolymer PLLA and a copolymer PLA96 (96% L4%D lactide), were hydrolytically degraded at 90°C in a phosphate buffered solution. Both polymers, PLLA and PLA96, showed an initial linear degradation rate, but with longer implantation periods the degradation rate decreased and total degradation was best described as an asymptotic. Mass loss of the copolymer PLA96 was twice that of PLLA. The chemical analysis of the in vitro predegraded polymers coincided for both the decrease in molecular weight and the thermal properties with physiologically degraded poly(lactide). The results of this study show that although the degradation temperature is well above the glass transition temperature and not comparable to physiological temperatures, there seems to be good correlation between the in vitro degraded material and physiologically degraded material. In vitro predegradation enables investigation of the entire degradation process of a polymer in a short-term study. Moreover, in vitro predegradation allows direct comparison of the degradation rate of various polymers.     

Application of lignin as natural adhesion promoter in cotton fibre-reinforced poly(lactic acid) (PLA) composites

This study investigated how lignin—used as a natural adhesion promoter in biodegradable, thermoplastic cotton fibre-reinforced composites—influences the composites’ mechanical properties. Composites with fibre mass proportions of 40% were produced by compression moulding. Poly(lactic acid) (PLA), a biopolymer, served as matrix. Cotton/PLA composites with and without lignin content were manufactured. As reference samples of bast fibre-reinforced composites, kenaf/PLA composites were produced under the same conditions. The composites were tested for stiffness, tensile strength, elongation at break and impact strength. Fractured surfaces were analysed using scanning electron microscopy (SEM). The results of the composite investigations showed that the addition of lignin has an influence on the cotton/PLA composite characteristics. SEM investigations showed that the adhesion between fibre and matrix could be improved by the addition of lignin. Tensile characteristics like tensile strength and Young’s modulus could be improved clearly, while the impact properties were decreased.     

纳米纤维素/聚丁二酸丁二醇酯母粒改性聚乳酸的结晶与力学性能研究

以聚乳酸(PLA)为基体,聚丁二酸丁二醇酯(PBS)为增韧相,纳米纤维素(CNF)为增强相,采用不同的挤出温度,利用双螺杆挤出机熔融共混制备出一系列CNF/PBS母粒改性PLA复合材料。采用扫描电子显微镜、广角X射线衍射仪、差示扫描量热仪、偏光显微镜和万能试验机以及悬臂梁冲击试验机对复合材料的结晶和力学性能进行测试。结果表明:CNF可以起到异相成核的作用,但含量过多易引起团聚;与纯PLA相比,当CNF/PBS复合母粒的添加量为20%时,低温挤出的复合材料的结晶度、冲击强度分别提高了10.66%和141.51%,拉伸强度仅下降14.86%;当CNF/PBS母粒的添加为20%时,低温挤出的PLA基复合材料的结晶度、拉伸强度和冲击强度分别较高温下挤出的复合材料提高了11.61%、3.82%和16.37%。     

热模压工艺参数对聚乳酸/竹纤维复合材料拉伸强度的影响

采用四元二次通用旋转组合设计试验方法,研究了聚乳酸与竹纤维混合比例(PLA/BF)、竹纤维粒径、热模压温度、热模压时间等4个因素对聚乳酸/竹纤维复合材料拉伸强度(TS)的影响,并采用差示扫描量热仪(DSC)对复合材料进行了热力学表征。结果表明,PLA/BF、热模压温度、热模压时间对复合材料的拉伸强度影响显著,热模压温度与热模压时间存在显著的交互效应。DSC分析显示,PLA/BF、竹纤维粒径、热模压温度/时间工艺参数影响材料中PLA的结晶度(Xm)。本试验条件下的聚乳酸/竹纤维复合材料热模压优化工艺参数为:PLA/BF为90/10,竹纤维过100目标准筛,热压温度160℃,热压时间25min,理论最大TS为66.40MPa。     

A cellular automaton simulation of the degradation of porous polylactide scaffold: I. Effect of porosity

A cellular automaton method that includes a fabricating model for solvent casting/porogen leaching and a multiple-particle random walk model for oligomer molecular diffusion was used to simulate degradation behaviors and their dependence on the initial porosities (80%, 90% and 95%) of porous polylactide (PLA) scaffolds. Changes in the mass loss, molecular weight, numbers of PLA chains and ester groups, oligomer molecules release and average degradation rate with degradation time were investigated. The results show that during degradation, higher initial porosity resulted in greater molecular weight and a higher average number of ester groups and less mass loss, a lower number of oligomer molecules being released and a lower ratio of oligomer molecules remaining in the scaffold to those in the whole model. The average degradation rate and average number of PLA chains initially changed in direct proportion to the initial porosity, but there was an inverse change later in the degradation. In addition, no hollow structures were found in any of the scaffolds during the degradation, which indicates there was no dramatic autocatalytic phenomenon such as that seen for massive solid structures such as a plate in the porous PLA scaffold. The above simulated results are consistent with recent experimental reports, suggesting our simulating method has potential application in studying the degradation behaviors of porous scaffolds for tissue engineering.