PLA‐based nanoparticles with tunable hydrophobicity and degradation kinetics

In this work, the preparation of poly(lactic acid) (PLA)‐based degradable nanoparticles (NPs) with tunable hydrophobicity and degradation kinetics via starved emulsion free‐radical polymerization is studied. The synthesis of macromonomers, constituted of a tunable number of lactic acid units functionalized with 2‐hydroxyethyl methacrylate (HEMA), has been performed via bulk ring opening polymerization (ROP) of L, L‐ lactide catalyzed with 2‐ethylhexanoic acid tin (II) salt. Macromonomers were characterized through SEC, NMR, and FTIR and are subsequently polymerized through monomer‐starved semi‐batch emulsion polymerization (MSSEP). The effect on the polymerization process of various emulsifiers on the final diameter and particle size distribution has been studied. The resulting PLA‐based NPs are characterized by a narrow size distribution and a small particle size, down to 25 nm. Finally, a degradation study of selected NPs has been carried out to verify their degradability in aqueous media. It has been demonstrated the complete degradability of these PLA‐based NPs which occurs upon the hydrolysis of the PLA pendant chains leaving poly‐HEMA chains, which, being hydrophilic causes the NPs to dissolve in the aqueous suspension. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

聚乳酸/壳聚糖季铵盐皂石纳米复合材料的原位插层聚合及性能表征

通过两步法将2,3-环氧丙基三甲基氯化铵接枝壳聚糖合成了水溶性壳聚糖季铵盐(HTCC),以其为插层剂对稀有的新疆皂石(Saponite)黏土矿物进行有机改性,制备了壳聚糖季铵盐皂石(HTCC-saponite),并以其为助剂,以丙交酯为单体,通过原位插层聚合法制备了聚乳酸(PLA)/HTCC-saponite纳米复合材料.最优化合成条件:聚合反应温度150℃,辛酸亚锡加量2%(质量分数),HTCC-saponite加量1%(质量分数)、聚合反应时间16 h.微观结构分析表明HTCC-saponite具有插层与剥离共存的结构.采用X射线衍射(XRD)、透射电子显微镜(TEM)、热重分析(TG-DTG)和差示扫描量热仪(DSC)等对PLA/HTCC-saponite纳米复合材料的微观结构、形貌及热稳定性进行了表征和分析.结果表明,HTCC-saponite有效改善了PLA的结晶性能,提高PLA的热稳定性.抗菌测试结果表明,HTCC-saponite具有良好的抗菌性,并赋予PLA/HTCC-saponite复合材料较强的抑菌能力.     

Sustainability assessments of bio-based polymers

Bio-based polymers have become feasible alternatives to traditional petroleum-based plastics. However, the factors that influence the sustainability of bio-based polymers are often unclear. This paper reviews published life cycle assessments (LCAs) and commonly used LCA databases that quantify the environmental sustainability of bio-based polymers and summarizes the range of findings reported within the literature. LCA is discussed as a means for quantifying environmental impacts for a product from its cradle, or raw materials extraction, to the grave, or end of life. The results of LCAs from existing databases as well as peer-reviewed literature allow for the comparison of environmental impacts. This review compares standard database results for three bio-based polymers, polylactic acid (PLA), polyhydroxyalkanoate (PHA), and thermoplastic starch (TPS) with five common petroleum derived polymers. The literature showed that biopolymers, coming out of a relatively new industry, exhibit similar impacts compared to petroleum-based plastics. The studies reviewed herein focused mainly on global warming potential (GWP) and fossil resource depletion while largely ignoring other environmental impacts, some of which result in environmental tradeoffs. The studies reviewed also varied greatly in the scope of their assessment. Studies that included the end of life (EOL) reported much higher GWP results than those that limited the scope to resin or granule production. Including EOL in the LCA provides more comprehensive results for biopolymers, but simultaneously introduces greater amounts of uncertainty and variability. Little life-cycle data is available on the impacts of different manners of disposal, thus it will be critical for future sustainability assessments of biopolymers to include accurate end of life impacts.     

PAA对PLA流变性能和热性能的影响

通过熔融共混法制备了一系列的PLA/PAA共混物,考察了PLA/PAA共混体系的流变行为和热性能(结晶行为和热降解行为).FTIR测试结果证实PLA与PAA分子链之间形成了氢键网络.动态剪切流变测试和DSC测试均表明共混体系的流变行为和冷结晶行为会随着PAA含量的改变而改变,这可能是由于PLA与PAA的氢键作用受到PAA含量的影响.另外,DSC测试证实共混体系中的氢键网络还会受到试样热历史的影响.当PAA含量较低(低于5 wt%)时,PLA/PAA共混体系中PAA与PLA熔体两相的相分离不严重,使得PAA与PLA分子链能够较大限度地接触而形成较强的氢键作用,因而可以明显减缓增塑作用对黏度降低的影响.     

Different enantioselectivity of two types of poly(lactic acid) depolymerases toward poly(l-lactic acid) and poly(d-lactic acid)

Poly(lactic acid) (PLA) depolymerases are categorized into protease-type and lipase-type. Protease-types can hydrolyze poly(l-lactic acid) (PLLA) but not poly(d-lactic acid) (PDLA). Lipase-types, including cutinase-like enzyme (CLE) from Cryptococcus sp. strain S-2 preferentially hydrolyze PDLA. Both enzymes degraded not only PLA emulsion but also PLA film, in which amorphous region is preferentially attacked, but crystalline region can be also attacked. Stereocomplex PLA (sc-PLA) formed by 50:50 blending of PLLA and PDLA included no homo crystals, but a tiny homo crystallization peak appeared and crystallinity increased by 5% when attacked by CLE, although no significant change of molecular weight and crystalline size was found. Enantioselective degradation must occur in amorphous region of PLLA/PDLA film and preferentially hydrolyzed PDLA, resulting in a slightly excess amount of PLLA remained, which must be crystallized.     

Mapping Enzyme Activity on Tissue by Functional Mass Spectrometry Imaging

Enzymes are central components of most physiological processes, and are consequently implicated in various pathologies. High‐resolution maps of enzyme activity within tissues therefore represent powerful tools for elucidating enzymatic functions in health and disease. Here, we present a novel mass spectrometry imaging (MSI) method for assaying the spatial distribution of enzymatic activity directly from tissue. MSI analysis of tissue sections exposed to phospholipid substrates produced high‐resolution maps of phospholipase activity and specificity, which could subsequently be compared to histological images of the same section. Functional MSI thus represents a new and generalisable method for imaging biological activity in situ.     

Effect of surface texturing on friction behaviour of 3D printed polylactic acid (PLA)

Additive manufacturing is gaining a remarkable importance in manufacturing industries because of the ability to build parts with complex and intricate shapes. The most widely used material in additive manufacturing is the polymer. In this paper, circular textures have been 3D printed on the surface of Polylactic Acid (PLA) polymer using fused deposition modelling technique. Experiments were performed under dry and lubricated conditions by varying the texture size. The results were obtained for high and low speeds with varying loads of 10, 20, 30, 40 and 50 N. It was observed that coefficient of friction was minimum for texture T₂ at both high and low speeds under dry sliding conditions. This is due to the less real area of contact than texture T₁ and more effective formation of transfer film in case of texture T_3. The entrapment of wear debris is more effective which helps in the formation of transfer layer that acts as solid lubricant. Under lubricated conditions, it was observed that for low speed, texture T₃ has least coefficient of friction while at high speed texture T₁ resulted in the minimum coefficient of friction. This is mainly due to the more retention of lubricating oil for texture T₃ at low speed in comparison to the high speed. Surface analysis carried out for all the textures under dry sliding conditions revealed that the wear is mainly to adhesive and abrasive action.     

Synthesis of Biodegradable Chitosan-Poly(D,L-Lactide) Hybrid Amphiphiles via Ring Opening Graft Polymerization for Efficient Gene Carrier

Biodegradable chitosan-graft-poly(_D,L-lactide) (CHI-PLA) have been prepared by in situ ring-opening polymerization of _DL-lactide (LA) grafting from chitosan. The chemical structure and physical properties of these chitosan derivatives were characterized by FTIR, ¹H-NMR, TGA and XRD. Formation and characteristics of polymeric micelles based on these chitosan derivatives were studied by fluorescence spectroscopy and dynamic light scattering (DLS). The critical micelle concentration (CMC) in water varied from 0.048 to 0.021 mg/mL as PLA grafting percentage (GP) increased from 92% to 132%. The mean diameters of CHI-PLA micelles have been readily tuned by controlling GP and the pH of micelles solution. The quasi-spherical micelles were observed by transmission electron microscopy (TEM). In particular, complexes formed by CHI-PLA micelles and plasmid DNA were investigated by agarose gel electrophoresis. Compared to chitosan, it could exhibit enhanced transfection efficiency in some cases and lower cell toxicity, as confirmed by in vitro transfection and cytotoxicity assay in L929 cell lines. These results indicated that CHI-PLA may be used as a new nonviral gene delivery vector for future gene therapy applications.     

Synthesis and Immortal ROP of L-Lactide Using Copper Complex

In the present work, the -ONNO- tetradentate Schiff base ligand N, N′-bis (2-hydroxy-3-methoxybenzaldehyde) propylenediamine, [HMBPD] was synthesized. Further, complexation of this ligand with copper [HMBPD-Cu] was carried out and their reactivity for the ring-opening polymerization (ROP) of lactide (LA) has been studied. This monomeric copper complex is prepared by the reactions of copper solution with one molar equivalent of HMBPD Schiff-base ligand in ethanol under nitrogen atmosphere. This copper complex has been characterized by different spectroscopic methods, which showed square planner geometry. The copper complex is highly active towards ROP of LA. The rate of polymerization is heavily dependent on the initiator used. The copper complex allows controlled ring-opening polymerization as shown by the linear relationship between the percentage conversion and the number-average molecular weight. On the basis of literature reports, a mechanism for ROP of lactide has been proposed.     

Light olefins/paraffins sorption in poly(lactic acid) films

The sorption behavior of small molecules like ethane and ethylene in poly (lactic acid) (PLA) was studied in the temperature interval from 283 to 313 K using a Quartz Crystal Microbalance (QCM). The effect of the polymer structure on the solubility selectivity of PLA films with respect to these two gases was studied using polymer with two different L:D ratios (98:2 and 80:20). Furthermore, the polymer films were submitted to different thermal treatments to address the influence of crystallinity and morphology of the noncrystalline fraction on the sorption behavior. The sorption results obtained indicate that ethylene solubility coefficient in annealed PLA 98:2 is about 26% higher than that of ethane and 41% higher in PLA 98:2 melted. The dual‐mode sorption model describes well the sorption isotherms behavior, which is concave concerning the pressure axis. The fully amorphous PLA presents the better selectivity for the studied gases, since the crystallinity seems to produce a negative effect on the selectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1312–1319, 2008