聚乳酸的降解研究

探讨了聚乳酸水解以及超声波降解情况,利用傅立叶红外光谱(FT-IR)和凝胶渗透色谱仪测定其基团及相对分子质量变化。研究结果表明:聚乳酸超声波降解同其水解均为酯键断裂导致的,并且是酯键的任意断裂,在水解过程中聚乳酸质量损失快慢为盐酸溶液>磷酸缓冲液>去离子水;聚乳酸在水解过程中,相对分子量随降解时间的延长而减小,但在超声波作用30min下其质量有一定程度的损失而相对分子量反而增大,推断其可能发生了部分交联反应。     

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/聚乳酸可生物降解复合材料自然降解性能

通过注射成型工艺制备竹纤维/聚乳酸（BF/PLA）可生物降解复合材料。利用X射线衍射（XRD）、凝胶渗透色谱（GPC）、三维视频显微镜及扫描电镜（SEM）等分析手段研究了BF/PLA复合材料自然降解性能。研究结果表明：BF/PLA复合材料自然降解过程中BF首先降解,PLA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;复合材料颜色变深,表面变得粗糙不平,部分裸露的BF清晰可见,其拉伸强度和冲击强度逐渐下降。12个月后,BF/PLA复合材料质量损失率达到8.87%,PLA重均分子量降低了25.9%,复合材料的冲击强度和拉伸强度分别降低了44.0%和43.8%。BF/PLA可生物降解复合材料在土壤中的自然降解效率较低。     

聚乳酸/柠檬酸基聚酯共混物的降解性能

采用熔融共混制备了聚乳酸/柠檬酸基聚酯(PLA/PEGCA)共混物(质量比85/15),通过对共混物在缓冲溶液中的失重率、吸水率、PLA相对分子质量、表面形貌和力学性能的测定,研究了其降解行为,并同纯PLA做了对比。结果表明,由于PEGCA的亲水性强,缓冲溶液容易渗透到材料内部,所以PLA/PEGCA共混物相对于纯PLA有更好的降解能力。12周时,PLA/PEGCA共混物的失重率与吸水率分别为0.8%和13.0%,明显大于纯PLA。共混物中PLA的组分相对分子质量下降程度大于纯PLA。随着降解时间的延长,共混物表面出现明显裂纹,力学性能降低,12周后冲击强度和拉伸强度分别为7.8 MPa和11.3 MPa,而纯PLA变化不大。     

PBS的降解及其机理研究

通过配制碱、酸、水及土壤的培养液对聚丁二酸丁二醇酯(PBS)薄膜进行不同环境条件下的降解,对其降解机理进行研究。采用失重率及表面观察等手段对降解结果进行表征,结果表明:降解速率按照下列顺序递减:碱性降解土壤悬浮液降解酸性降解水降解。在降解的过程中,pH值呈逐渐减小的趋势。     

A10改性聚甲醛热稳定性的研究

通过分子量测定、红外光谱分析(FT-IR)研究了聚甲醛(POM)的热降解机理并根据降解机理采用稳定剂A10对POM进行共混改性。运用热失重(TG)、差动扫描(DSC)、机械力学测试探讨了A10对聚甲醛改性后热稳定性能的影响。研究结果显示:热降解产生新的端基,熔融温度高于200℃时POM大分子链的断裂加快;稳定剂A10改性POM纤维在100℃老化处理250h后纤维断裂强度和断裂伸长保持率分别达95%以上和89%以上;随着稳定剂A10比例增大,热分解活化能增加,聚甲醛的热失重率逐渐降低,热分解温度升高。     

纳米纤维素/聚乳酸复合材料的降解性能

目的研究纳米纤维素/聚乳酸(NCC/PLA)复合薄膜在不同降解条件下的降解情况。方法在p H值为3,7,11的溶液及紫外光照射条件下,降解自制的复合薄膜,通过测失重率、扫描电子显微镜观察、X射线光电子能谱分析等手段,分析p H值、光照和NCC的添加与复合材料降解能力间的关系,研究其降解机理,并与纯PLA薄膜对比。结果 NCC/PLA复合薄膜在碱性条件下质量损失最快,酸性稍慢,中性更慢,紫外光照射下最慢,复合薄膜质量损失均比纯PLA薄膜多。在p H值为3和7的溶液及紫外光照射降解后,NCC/PLA复合薄膜氧碳原子数量的比值均比未降解时增大,分别提高了35.16%,36.66%,38.65%。结论 NCC的添加提高了NCC/PLA复合薄膜的降解性能,在不同降解过程中,薄膜表面C原子所占比例减少,相对地O原子所占比例增加,氧碳原子数量的比值增大。     

乳酸-乙醇酸共聚物的制备及降解性能研究

以L-乳酸(L-LA)和乙醇酸(GA)为原料(L-LA和GA投料摩尔比为80∶20),二水合氯化亚锡和对甲苯磺酸(TSA)为复合催化剂,采用直接熔融缩聚法制OLGA预聚物,然后在扩链剂六亚甲基二异氰酸酯(HDI)存在下进行熔融扩链,最终得到较高分子量的乳酸-乙醇酸共聚物(PLGA),其数均分子量和重均分子量分别为5.5×104和1.3×105。将溶液浇铸法制备的PLGA薄膜在37℃、pH=7.3～7.4的磷酸盐缓冲液(PBS)中进行降解实验,采用pH分析、失重率测量、GPC、SEM、FT-IR等方法研究了PLGA薄膜的降解行为,并对降解机理进行了初步探讨。结果表明,随着降解的进行,PLGA薄膜的相对分子量和质量都会逐渐下降,在降解反应进行的前21天中,相对分子量的减小较明显,21天之后质量损失较明显。结合FT-IR谱图的研究,分析可知PLGA的降解主要是通过酯键的水解实现的。     

多臂星形聚乙二醇-聚乳酸嵌段共聚物的降解特性EI北大核心CSCD

采用直接法合成了线型和多臂星形聚乙二醇-聚L-乳酸嵌段共聚物((PLLA-b-PEG-b-PLLA和sPEG-b-PLLA)。研究了3种嵌段共聚物在37℃、pH=7.2的磷酸盐缓冲液中的降解机理。结果表明,共聚物降解后失重明显,亲水性降低;降解一定时间后共聚物的相对分子质量分布呈双峰分布,随着降解的进行,较低相对分子质量组分的相对分子质量并没有发生明显的变化。XRD数据表明,降解前后的主要组成为结晶PLLA嵌段;1H-NMR分析证实,共聚物的降解过程中PEG嵌段和PLLA嵌段内部的降解程度很小。说明sPEG-b-PLLA在中性水性体系中的降解主要发生在连接PLLA和PEG的酯键上,而PLLA嵌段则由于处于结晶态,降解程度很低。     

抗菌聚乳酸薄膜的性能研究

采用溶液共混的方法制得Ag型抗菌剂含量不同的抗菌聚乳酸(PLA)薄膜试样,研究表明,添加少量Ag型抗菌剂即可使薄膜具有抗菌功能,添加1%的抗菌剂薄膜抗菌率达到100%,且薄膜具有抗菌长效性,Ag型抗菌剂在PLA薄膜中不溶出.力学性能测试发现,Ag型抗菌剂的加入对薄膜拉伸强度和断裂伸长率影响不大;土壤降解实验发现,在16周降解过程中,薄膜的质量损失较少,但相对分子质量变化较大,抗菌剂的加入对薄膜的降解性能基本元影响.     

聚乳酸的合成与性能研究

以乳酸单体为原料,采用直接缩聚法合成了具有较高粘均分子质量的聚乳酸,用红外光谱、H—NMR等方法初步表征了聚乳酸的结构。研究了聚乳酸的亲水性和降解性。结果表明,聚乳酸的水接触角和吸水率分别为79．30和2．8％,说明聚乳酸具有一定的亲水性。聚乳酸在降解过程中表现为体型降解特点。粘均分子量和降解温度对聚乳酸的降解规律影响不大,但低分子量聚乳酸及聚乳酸在较高降解温度下的降解程度和初期降解速率明显大于高分子量聚乳酸及较低降解温度。本文还研究了聚乳酸粘均分子量在降解过程中的变化情况。     

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.     

An Investigation of the Synthesis of Poly(D, L-Lactic Acid) and Preparation of Microspheres Containing Indomethacin

Seven batches of poly(D, L-lactic acid) (PLA) were prepared from D, L-lactic acid using tetraphenyltin or zinc acetate as a catalyst. The samples of PLA were characterized by terminal group analysis, gel permeation chromatography, infrared analysis, and differential scanning calorimetry. Polymerization conditions such as the time of reaction and the type of catalyst affected the molecular weight of PLA. Microspheres containing indomethacin were prepared by the oil/water (o/w) solvent evaporation technique using different formulations and process variables. The in vitro release of indornethacin in phosphate buffer was found to be dependent on the molecular weight of PLA and also on the type and amount of adjuvants used. The batch of microspheres containing 5% cholesterol released the drug at a slow controlled rate (29%, 65%. and 85% in 1, 7, and 24 hr, respectively). The results of F test for the microspheres revealed that there is no significant direrence between the Higuchi model and the power law equation. The drug was released by a dimsion mechanism from the microspheres.     

An Investigation of the Synthesis of Poly(D,L-Lactic Acid) and Preparation of Microspheres Containing Indomethacin

Abstract

Seven batches of poly(D, L-lactic acid) (PLA) were prepared from D, L-lactic acid using tetraphenyltin or zinc acetate as a catalyst. The samples of PLA were characterized by terminal group analysis, gel permeation chromatography, infrared analysis, and differential scanning calorimetry. Polymerization conditions such as the time of reaction and the type of catalyst affected the molecular weight of PLA. Microspheres containing indomethacin were prepared by the oil/water (o/w) solvent evaporation technique using different formulations and process variables. The in vitro release of indornethacin in phosphate buffer was found to be dependent on the molecular weight of PLA and also on the type and amount of adjuvants used. The batch of microspheres containing 5% cholesterol released the drug at a slow controlled rate (29%, 65%. and 85% in 1, 7, and 24 hr, respectively). The results of F test for the microspheres revealed that there is no significant direrence between the Higuchi model and the power law equation. The drug was released by a dimsion mechanism from the microspheres.     

亚磷酸三苯酯调控聚乳酸/氯化铁共混体系的降解行为和性能

用熔融共混法制备了氯化铁(FeCl₃)催化聚乳酸(PLA)快速降解材料。PLA材料降解的速率提高了10倍,但是PLA/FeCl₃在加工过程中分子量大幅度减小,使力学性能和可加工性能降低。为了减小PLA/FeCl₃在熔融加工中的过度降解,将有优良扩链和增塑效果的亚磷酸三苯酯(TPPi)引入PLA/FeCl₃体系中,用熔融共混制备TPPi改性PLA/FeCl₃材料,使其具有一定的综合力学性能。通过碱溶液降解实验和多种测试研究了样品的降解速率和综合性能。结果表明,TPPi和FeCl₃ 的添加量之比为3∶1的P3-1样品性能最优,拉伸强度和弯曲强度分别达到43.78 MPa和99.04 MPa,在碱液中降解8d其质量损失率为65.76%,远大于纯聚乳酸的4.67%。含2.95 phr FeCl₃的样品能在碱液中产生高降解速率,加工时不发生过度降解,由此制备出一种可快速降解并保持良好力学性能的聚乳酸改性材料。     

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.     

High-pressure crystallization of poly(lactic acid) with and without N2 atmosphere protection

High-pressure crystallization experiments of poly(lactic acid) (PLA) were conducted under air and N₂ atmosphere. Compared with the sharp decrease of the molecular weight of air sample from 1.63 × 10⁵ to 3.11 × 10⁴, the weight loss of N₂ protection sample was successfully restricted to the value below 10 %. Stable α-crystals were generated in both air and N₂ protection samples which both exhibited very high crystallinity up to 66.3 and 64.5 %, respectively. It is high pressure that leads to the perfect crystalline structure by inducing crystalline reorganization and lamellar thickening. A diffraction streak appeared in the 2D-SAXS pattern of air sample in contrast to the broad scattering signal in N₂ protection sample, implying the formation of oriented crystals during PLA degradation. As observed from scanning electron microscopy, the spherulite size of air sample was larger than that of N₂ protection sample, for the radius growth rate of PLA crystals increased as molecular weight decreased. Accordingly, N₂ atmosphere protection can not only effectively prevent PLA from degradation, but also acquire highly crystallized PLA.     

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。