Properties and morphology of poly(L‐lactide). III. Effects of initial crystallinity on long‐term in vitro hydrolysis of high molecular weight poly(L‐lactide) film in phosphate‐buffered solution

The effects of crystallinity (x_c) on the hydrolysis of high molecular weight poly(L ‐lactide) (PLLA) films in a phosphate‐buffered solution at 37°C was investigated by gel permeation chromatography, tensile testing, differential scanning calorimetry, scanning electron microscopy, and polarizing optical microscopy. The change in molecular weight distribution and surface morphology of the PLLA films after hydrolysis revealed that the hydrolysis of PLLA film in a phosphate‐buffered solution proceeded homogeneously along the film cross section, mainly via the bulk‐erosion mechanism. The induction period until the start of the decrease in mass remaining and the tensile strength became longer with a decrease in the initial x_c of the PLLA films. The rate of molecular weight reduction was higher as the initial x_c of the PLLA films increased when hydrolysis was carried out up to 24 months. Melting and glass transition temperatures of the PLLA films increased in the first 12 months of hydrolysis, while they decreased in another 24 months, irrespective of the initial x_c. The x_c value of the PLLA films increased monotonously by hydrolysis. The lamella disorientation in PLLA spherulites after hydrolysis implied that the hydrolysis of PLLA chains occurred predominantly in the amorphous region between the crystalline regions in the spherulites. The area of a specific molecular weight in GPC spectra at 36 months increased with increase in the initial x_c of the PLLA film, suggesting that the specific peak should be due to the component of one fold in the crystalline region. The reason for enhanced hydrolysis of PLLA films having higher initial crystallinities was discussed in terms of tie chains and terminal groups of PLLA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1452–1464, 2000     

可生物降解多嵌段聚乳酸共聚物合成研究

以氧化锌为催化剂,使左旋丙交酯(LLA)与聚乙二醇(PEG600)开环共聚,得到三嵌段(HO PLLA PEG PLLA OH)预聚物;再以甲苯二异氰酸酯TD1 80为扩链剂对其进行扩链,得到多嵌段共聚物.采用核磁共振、红外光谱、凝胶渗透色谱等对目标产物的结构、分子量分布进行了表征;同时用变温红外法研究了与LLA结晶相关谱带的位置,并对其进行了归属.     

Crystallisation and spherulite morphology of polylactide stereocomplex

In this study we investigated the crystallisation behaviours of stereocomplex crystals in poly(l ‐lactic acid)/poly(d ‐lactic acid) ( PLLA/PDLA) blends (LD blends) of various weight ratios. The crystallisation and melting behaviours were studied using DSC, and the crystal structure was analysed through wide‐angle X‐ray diffraction. The morphology of homocrystals and stereocomplex crystals in the blends was examined using a hot‐stage polarising microscope and a scanning electron microscope. The DSC results showed that homocrystals and stereocomplex crystals were present in all LD blends except that with 50 wt% PLLA/50 wt% PDLA; in this blend, only stereocomplex crystals were present. The regime II → III transition temperature of stereocomplex crystals in a Lauritzen–Hoffman plot of the LD blends was determined to be 165 °C. A concentric spherulite consisting of stereocomplex crystals and homocrystals formed under two‐step isothermal crystallisation conditions with three growth stages was observed. The confined spherulitic growth rate in the concentric spherulite and the unrestricted spherulitic growth rate in individual spherulites were also analysed. © 2018 Society of Chemical Industry     

Bioactive Polylactide Fibrous Materials Prepared by Crazing Mechanism

Bioactive suture materials made of biodegradable polymers containing biologically active substances are increasingly demanded in contemporary surgical practice. Herein, the functional fibrous materials are produced by structural modification of polylactide (PLA) fibers according to the crazing mechanism in water–ethanol solutions. The threshold of ethanol concentration, at which the breaking elongation of the polymer substantially increases (up to 600–700%), is found to be 30 wt%. The crazing mechanism is employed to fill the porous structure of PLA fibers by different antiseptic substances (brilliant green, iodine, and fuchsin). PLA loaded by 0.8 wt% of brilliant green exhibits antimicrobial activity on Escherichia coli and Candida guilliermondii. The additive is released stepwise for a prolongated time period (2.5 months). The addition of 1–6 wt% iodine dramatically accelerates the polymer degradation in sodium‐phosphate buffer solution at 37 °C. The obtained filled fibers may possess great interest for producing suture materials with prolonged action of functional components and variable degradation times.     

Chitosan‐g‐Polyester Microspheres: Effect of Length and Composition of Grafted Chains

Hydrophobic segments made of oligo(l,l ‐ or d,l ‐lactides) or poly(l,l ‐lactide) are grafted onto chitosan backbone in order to use their amphiphilic behavior to prepare degradable microcarriers intended to be used for tissue engineering. Hydrophilic–lipophilic balance of these copolymers is adjusted playing on the respective length of their hydrophilic and hydrophobic moieties. Thanks to their self‐emulsifying properties, these graft copolymers are processed into microspheres in the absence of hydrophilic emulsifier commonly added in the aqueous phase of the oil/water emulsion. The copolymers containing amorphous oligolactide segments of medium length are demonstrated to be the most effective ones for microparticle fabrication. The microparticles are characterized using SEM, EDX, and FTIR. The reactivity of amine group is demonstrated using fluorescein isothiocyanate staining. The resulting microspheres disclose a porous core and a shell enriched by the hydrophilic polysaccharide moieties. Stabilization of the oil/water interface during the microsphere fabrication, total yield, size distribution, and microparticle surface morphology are mainly affected by the macromolecular features of the copolymers.     

Evolution of the mechanical properties and estimation of the useful lifespan of poly(lactic acid) based compounds

The useful lifespans of a poly(lactic acid)/poly(methyl methacrylate) (PLA/PMMA) 80/20 (wt%) blend and a poly(lactic acid)/dioctyl adipate/talc (PLA/DOA/talc) compound have been estimated by applying an Arrhenius relationship to the evolution of the mechanical properties whilst ageing. The studied PLA based systems showed lower activation energies (ca 8 ? 20 kJ mol^?1) than those reported in the literature for other synthetic thermoplastics, indicating lower thermo‐oxidative stability. However, both systems were interesting choices for semi‐durable applications in terms of useful lifespan estimations. The PLA/PMMA blend showed a drastic loss in stiffness at T_g due to its almost amorphous structure whereas, in contrast, PLA/DOA/talc showed acceptable mechanical properties above its glass transition temperature due to its semicrystalline structure. © 2018 Society of Chemical Industry     

单螺杆挤出机计量段模拟研究

针对3种不同类型聚乳酸(PLA)专用螺杆的计量段结构,运用Polyflow软件进行三维流场模拟3种不同类型混炼结构,分析聚乳酸挤出过程的三维等温流场。结果表明:在相同的工艺条件下,不同的单螺杆结构,流道内聚乳酸各物理量的值存在较大差异性;普通型单螺杆的熔体的轴向速度和压力较大,利于螺杆挤出过程,但熔体剪切速率小、熔体黏度大,从而导致挤出熔体质量较差;菠萝型单螺杆的熔体的轴向速度和剪切速率较大且黏度值较小,因此具有较好的塑化能力;菠萝型和销钉型单螺杆在流道内会出现环流的情况,不利于熔体输送。     

Synthesis and characterization of AB‐type copolymers poly(L‐lactide)‐block‐poly(methyl methacrylate) via a convenient route combining ROP and ATRP from a dual initiator

Diblock copolymers of poly(L ‐lactide)‐block‐poly(methyl methacrylate) (PLLA‐b‐PMMA) were synthesized through a sequential two‐step strategy, which combines ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP), using a bifunctional initiator, 2,2,2‐trichloroethanol. The trichloro‐terminated poly(L ‐lactide) (PLLA‐Cl) with high molecular weight (M_n,GPC = 1–12 × 10⁴ g/mol) was presynthesized through bulk ROP of L ‐lactide (L ‐LA), initiated by the hydroxyl group of the double‐headed initiator, with tin(II) octoate (Sn(Oct)₂) as catalyst. The second segment of the block copolymer was synthesized by the ATRP of methyl methacrylate (MMA), with PLLA‐Cl as macroinitiator and CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as catalyst, and dimethyl sulfoxide (DMSO) was chosen as reaction medium due to the poor solubility of the macroinitiator in conventional solvents at the reaction temperature. The trichloroethoxyl terminal group of the macroinitiator was confirmed by Fourier transform infrared spectroscopy (FTIR) and ¹H‐NMR spectroscopy. The comprehensive results from GPC, FTIR, ¹H‐NMR analysis indicate that diblock copolymers PLLA‐b‐PMMA (M_n,GPC = 5–13 × 10⁴ g/mol) with desired molecular composition were obtained by changing the molar ratio of monomer/initiator. DSC, XRD, and TG analyses establish that the crystallization of copolymers is inhibited with the introduction of PMMA segment, which will be beneficial to ameliorating the brittleness, and furthermore, to improving the thermal performance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

细菌纤维素及其酯化产物与聚乳酸的复合材料的制备与表征

细菌纤维素(BC)经由多种有机酸(乙酸、正己酸、月桂酸)表面酯化,得到细菌纤维素乙酸酯(C2-BC)、细菌纤维素正己酸酯(C6-BC)、细菌纤维素月桂酸酯(C12-BC),将BC及酯化产物分别加入到聚乳酸(PLA)溶液,采用热致相分离技术(TIPS)制备出BC(BC酯化产物)/PLA复合材料,红外光谱、扫描电镜、差热分析和热重分析结果显示,BC以及酯化产物均匀分布在PLA中,制备的复合材料具有多孔结构,酯化产物的添加提高了PLA的结晶度,但是对PLA链的移动性没有太大影响。同时,BC及其酯化产物的的引入,提高了PLA的降解温度,并且随着酯化支链的长度增加,杨氏模量和抗拉强度也相应有所提高。