Structure and properties of clay nano‐biocomposites based on poly(lactic acid) plasticized with polyadipates

The use of nano‐biocomposites based on plasticized poly(lactic acid) (PLA) has been proposed as a way to improve the polymer ductility and to expand PLA applications window. Novative nano‐biocomposites were elaborated with PLA plasticized by polyadipates (15 wt%) with different molar masses (from 1500 to 2500 Da), with 2.1 wt% of an organo‐modified montmorillonite (O‐MMT). These materials showed enhanced ductility and barrier properties. The clay was swelled in liquid polyadipates prior to their blending with PLA to facilitate chains intercalation and nanofiller exfoliation during melt‐blending. In certain processing conditions, quite homogenous and exfoliated structures were obtained, as shown by X‐ray diffraction (XRD) and transmission electronic microscopy (TEM) results. Irrespective of the average molar mass of the polyadipate, the clay addition induced a reduction in around 25% in oxygen transmission rate (OTR) without an important detriment in tensile properties. Nano‐biocomposites prepared with higher molar masses polyadipates showed the highest thermal stability as well as the lowest OTR, resulting in very promising and novative materials for different applications such as soft packaging. Copyright © 2010 John Wiley & Sons, Ltd.     

生物基超韧聚乳酸复合材料的制备与性能

采用来源于可再生资源的聚醚酰胺弹性体（PEBA）增韧聚乳酸（PLA）制备超韧聚乳酸（PLA/PEBA-GMA）复合材料.为了提高PEBA与PLA之间的相容性,选择极性单体甲基丙烯酸缩水甘油酯（GMA）、共接枝单体乙烯基吡咯烷酮（NVP）及引发剂过氧化二异丙苯（DCP）对PEBA进行接枝改性制备PEBA-GMA.研究了接枝单体组分的用量（m/g）对PLA/PEBA-GMA复合材料性能的影响.研究发现,随着接枝单体组分用量的提高,复合材料的缺口冲击强度逐渐增大,当接枝单体组分GMA,NVP和DCP的用量分别为2.5,2.5和0.25 g时,复合材料的冲击强度高达88.6 kJ/m²,断裂伸长率为164.1%.研究表明,在熔融共混过程中,聚乳酸的端基（—OH和—COOH）与PEBA-GMA上环氧基团发生反应,有效改善两相间的界面相容性,随着接枝单体组分比例的提高,分散相PEBA-GMA的粒子尺寸逐渐减小且分布均匀.     

Preparation and characterization of benzoyl‐hydrazide‐derivatized poly(lactic acid) and γ‐cyclodextrin inclusion complex and its effect on the performance of poly(lactic acid)

A nucleating agent, benzyl‐hydrazide‐derivatized poly(lactic acid) (PLA) and γ‐cyclodextrin inclusion complex (PLA‐IC‐BH), was synthesized through a series of reactions. Poly(lactic acid) and γ‐cyclodextrin inclusion complex (PLA‐IC) was first obtained by ultrasonic co‐precipitation, which was then subjected to carboxylation, acylation, and amidation using benzoyl hydrazine and thionyl chloride. The composition and structure of PLA‐IC‐BH was confirmed by ¹H nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. PLA/PLA‐IC‐BH composites were prepared by melt blending and a hot‐press forming process. Mechanical properties, thermal stabilities, and crystallization behaviors of PLA/PLA‐IC‐BH samples were investigated by thermogravimetric analysis, differential scanning calorimetry (DSC), polarized optical microscopy (POM), rheological analysis, and so on. Mechanical testing and thermogravimetric analysis showed that the tensile strengths, impact properties, and thermal stabilities of PLA/PLA‐IC‐BH composites were improved significantly compared to pure PLA and PLA/PLA‐IC. DSC results showed that crystallinity of PLA was increased from 5.17% to 38.93% after introduction of PLA‐IC‐BH. POM results showed that PLA‐IC‐BH acted as a nucleating agent for PLA and enhanced its crystallization rate. Rotational rheological behaviors of PLA/PLA‐IC‐BH demonstrated that incorporation of PLA‐IC‐BH increased the rigidity of the network structure of the PLA matrix. Compared to those of PLA, the maximum torque and apparent viscosity of PLA/PLA‐IC‐BH composites were increased by 55.56% and 25.59%, respectively. Copyright © 2017 John Wiley & Sons, Ltd.     

Chemical modification of poly(lactic acid) induced by thermal decomposition of N‐acetoxy‐phthalimide during extrusion

Chemical modification of poly(lactic acid) (PLA) with N‐acetoxy‐phthalimide (NAPI) was performed in the melt by reactive extrusion, without using any peroxide initiator. The aminyl and nitroxide radicals produced from the NAPI thermal degradation, were, respectively, used (a) to create PLA macroradicals, and (b) to functionalize the PLA samples through nitroxide radical coupling. Depending on the extrusion temperature and the initial NAPI concentration, grafting rates up to 0.24 mol % were measured, modifying the PLA optical properties. This study represents an original new way of modification of PLA without the use of conventional peroxide initiators. Indeed, the undesirable side reactions (PLA branching or crosslinking) usually observed when using peroxides to initiate the radical grafting of PLA were avoided when using NAPI. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 120–129     

Compatible and tearing properties of poly(lactic acid)/poly(ethylene glutaric‐co‐terephthalate) copolyester blends

Fourier transform infrared and nuclear magnetic resonance results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the hydroxyl groups of FePol (FP) molecules during the melt‐blending of PLA_xFP_y specimens. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) experiments of PLA and PLA/FP specimens suggest that only small amounts of poor PLA and/or FP crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature, and onset re‐crystallization temperature values of PLA/FP specimens reduce gradually as their FP contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA reduce to a minimum value as the FP contents of PLA_xFP_y specimens reach 6 wt %. Further DMA and morphological analysis of PLA/FP specimens reveal that FP molecules are compatible with PLA molecules at FP contents equal to or less than 6 wt %, as no distinguished phase‐separated FP droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/FP specimens, respectively. In contrast to PLA, the FP specimen exhibits highly deformable and tearing properties. After blending proper amounts of FP in PLA, the inherent brittle deformation and poor tearing behavior of PLA were successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tearing properties of PLA/FP specimens are proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 913–920, 2010     

The influence of multiple modified MMT on the thermal and fire behavior of poly (lactic acid) nanocomposites

This work reported the preparation and physical properties of biodegradable nanocomposites fabricated using polylactic acid (PLA) and multiple organic modified montmorillonite (MMT). In order to improve the chemical compatibility between PLA and Na‐MMT, the surface of Na‐MMT was first organically modified by cetyl trimethyl ammonium bromide (CTAB) and resorcinol bis(diphenyl phosphate) (RDP) using ion‐exchange and adsorption technique. Both Fourier transform infrared and X‐ray diffraction (XRD) results indicated that CTAB and RDP molecules were intercalated into the galleries of MMT sheets to enlarge the interlayer spacing. Then, the PLA/MMT nanocomposites were prepared by a simple melt‐blending method. The XRD and TEM results of the nanocomposites indicated that the PLA polymer chains inserted into the galleries of co‐modified MMT (C‐MMT) and contained disorderedly intercalated layered silicate layers within a PLA matrix. The C‐MMT nanolayers were homogenously dispersed in PLA matrix, resulting in various property enhancement. The fabricated PLA/C‐MMT nanocomposites with 5.0 wt% addition showed significant enhancements (176%) in the storage modulus compared to that of neat PLA. The thermal stability and fire resistance were also remarkably improved. These improvements are probably because of both the physical barrier effect of the MMT nanosheets and charring effect of the C‐MMT. Copyright © 2015 John Wiley & Sons, Ltd.     

Structure‐property relationship,rheological behavior,and thermal degradability of poly(lactic acid)/fulvic acid amide composites

Fulvic acid amide (FAA) was synthesized with fulvic acid (FA) and urea. The structure of FAA was characterized by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Poly(lactic acid)/fulvic acid amide (PLA/FAA) composites were prepared by melt blending and compression molding. The nucleation effect of FAA on PLA was investigated by differential scanning calorimetry and polarized optical microscopy. Structure‐property relationship of PLA/FAA composites showed that FAA accelerated crystallization rate of PLA and improved toughness of PLA. Rotational rheological behavior of PLA/FAA composites showed that FAA increased the storage modulus of PLA. Capillary rheological analysis showed that the apparent viscosities of PLA composites were highly increased after the introduction of the FAA nucleating agent. Moreover, thermogravimetric analysis demonstrated that thermal degradability of PLA/FAA composites has been increased significantly compared with the neat PLA.     

Thermal properties and cold crystallization kinetics of surface-treated banana fiber (BF)-reinforced poly(lactic acid) (PLA) nanocomposites

Nucleation capacity of organically modified natural montmorillonite within the surface-treated banana fiber (BF)-reinforced PLA biocomposites has been studied using DSC analysis in the present investigation. Both the surface treatments and nanoclays play vital roles in the variation in nucleation process of PLA during cold crystallization process. Biocomposite made up of silane-treated BF and its bionanocomposite prepared using cloisite 30B (C30B) were showed superior nucleation parameters, n and K values, in the Avrami plots. Enhanced equilibrium melting point and lower E _a suggests the reinforcing effect imparted by the BF surface treatments and C30B within the PLA matrix. Even though, Louritzen–Hoffmann theory was revealed that no change in crystallization regimes of PLA even after the biocomposite and bionanocomposite preparation. TG analysis revealed better heat barrier capacity for all the biocomposites and bionanocomposites in comparison with virgin PLA (V-PLA). Increased storage modulus values for biocomposites and bionanocomposites also confirm the reinforcing effects of the fillers. Heat deflection temperature and the flammability studies concluded better application window for newly developed materials than that V-PLA.     

Biocomposites based on ramie fibers and poly(L‐lactic acid) (PLLA): morphology and properties

We herein report effects of morphology of PLLA and natural fiber on combination properties of biocomposites based on PLLA and ramie fibers. For this purpose, short ramie fiber (FIB), ramie fabric (FAB), PLLA film (FPLLA), and PLLA powder (PPLLA) were used to investigate the structure–property relationship of PLLA biocomposites with 30 wt% ramie fiber prepared by hot compression molding. It is revealed that mechanical properties of biocomposites are strongly dependent on the morphology of PLLA and FAB. DMA test shows that the improved storage modulus was due to the better dispersion of FIB. DSC and POM tests show that PLLA/FIB biocomposites have the highest spherulite growth rate. TGA test shows that char residue at high temperature is affected by the dispersion of PLLA and ramie fiber. SEM images exhibit the different interfacial adhesion character of FIB and FAB in the PLLA matrix after the ramie fiber treated with alkali and silane. PLLA/FAB biocomposites have not only better anti‐dripping properties when burning but also better aging resistance in UV‐irradiation hydrothermal aging, and which can be attributed to fiber bundle and laminated PLLA biocomposites structure. Copyright © 2010 John Wiley & Sons, Ltd.     

The effect of free radical reactions on structure and properties of poly(lactic acid) (PLA) based blends

The blending of PLA with poly(butylene-adipate-co-terephthalate) (PBAT) is a promising strategy to achieve a toughened multiphase material. The blends ductility could be further improved through reactive compatibilization, i.e. inducing the formation of comb PLA-PBAT copolymers during the melt blending. In the present work a non-selective strategy was adopted which consisted in the use of a peroxide, 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane. The phase morphology development and the final properties (torque, fluidity in the melt, tensile behaviour, thermal and dynamical-mechanical features) of the blends were studied as a function of the peroxide concentration. The elongation at break was improved up to a maximum value thanks to this approach and a corresponding minimum was observed in the value of the dispersed phase diameter. A structural characterization of the macromolecules formed during the reactive process was attempted by using size exclusion chromatography of the blends and comparison with the pure polymers obtained by processing in the presence of the peroxide.     

Three‐dimensional printing of poly(lactic acid) bio‐based composites with sugarcane bagasse fiber: Effect of printing orientation on tensile performance

The cellulose fiber was extracted from the abandoned crop sugarcane bagasse (SCB) by means of chemical treatment methods. Poly(lactic acid) (PLA) bio‐based composites with SCB were prepared through fused deposition modeling (FDM) 3D‐printing technology, and the morphologies, mechanical properties, crystallization properties, and thermal stability of 3D‐printed composites were investigated. Compared with the neat PLA, the incorporation of SCB into PLA reduces the tensile strength and flexural strength of 3D‐printed samples but increases the flexural modulus. The difference in tensile performance and bending performance is that the tensile strength of 3D‐printed samples is best when the SCB content is 6 wt%, while the flexural modulus continuously decreases as the SCB content increases. Furthermore, the effects of various printing methods on the tensile performance of 3D‐printed samples were explored via modifying G‐code of 3D models. The results indicate that the optimum SCB fiber content is identical for all printing methods except method “vertical.” Due to the fibers and molecular chains are oriented to varying degrees with altering raster angle in 3D‐printed samples, the fully oriented sample printed by method “parallel” has a better tensile strength. Besides, SCB exhibits enough high thermal decomposition temperature to meet requirements for melt extrusion processing of PLA composites, and SCB fiber is capable of promoting the crystallization of PLA.     

聚(ε-己内酯-L-丙交酯)无规共聚物与聚乳酸共混材料的制备与性能

通过开环聚合,合成不同比例的ε-己内酯(ε-CL)与L-丙交酯(L-LA)的无规共聚物P(CL/LLA)。 将上述共聚物P(CL/LLA)与聚乳酸(PLLA)共混,制备了PLA/P(CL/LLA)共混材料。 并对其相容性、热性能、力学性能进行了研究。 结果表明,共聚物P(CL/LLA)与PLA相容性与共聚物中LA单元含量和链段的平均长度有密切关系,P(CL/LLA)中LA链段平均长度达到3.4以上时,可以与PLA很好的相互作用。 同时共聚物P(CL/LLA)中-CL-链段有很好的柔性,可以很好的改善PLLA的韧性,使PLLA材料的断裂伸长率达到500%以上。     

Influences of poly(lactic acid)‐grafted carbon nanotube on thermal,mechanical, and electrical properties of poly(lactic acid)

Poly(lactic acid)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PLA) were prepared by the direct melt‐polycondensation of L ‐lactic acid with carboxylic acid‐functionalized MWNT (MWNT‐COOH) and then mixed with a commercially available neat PLA to prepare PLA/MWNT‐g‐PLA nanocomposites. Morphological, thermal, mechanical, and electrical characteristics of PLA/MWNT‐g‐PLA nanocomposites were investigated as a function of the MWNT content and compared with those of the neat PLA, PLA/MWNT, and PLA/MWNT‐COOH nanocomposites. It was identified from FE‐SEM images that PLA/MWNT‐g‐PLA nanocomposites exhibit good dispersion of MWNT‐g‐PLA in the PLA matrix, while PLA/MWNT and PLA/MWNT‐COOH nanocomposites display MWNT aggregates. As a result, initial moduli and tensile strengths of PLA/MWNT‐g‐PLA composites are much higher than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, which stems from the efficient reinforcing effect of MWNT‐g‐PLA in the PLA matrix. In addition, the crystallization rate of PLA/MWNT‐g‐PLA nanocomposites is faster than those of neat PLA, PLA/MWNT, and PLA/MWNT‐COOH, since MWNT‐g‐PLA dispersed in the PLA matrix serves efficiently as a nucleating agent. It is interesting that, unlike PLA/MWNT nanocomposites, surface resistivities of PLA/MWNT‐g‐PLA nanocomposites did not change noticeably depending on the MWNT content, demonstrating that MWNTs in PLA/MWNT‐g‐PLA are wrapped with the PLA chains of MWNT‐g‐PLA. Copyright © 2008 John Wiley & Sons, Ltd.     

Silkworm silk/poly(lactic acid) biocomposites: Dynamic mechanical, thermal and biodegradable properties

Silkworm silk/Poly(lactic acid) (silk/PLA) biocomposites with potential for environmental engineering applications were prepared by using melting compound methods. By means of Dynamic mechanical analysis (DMA), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), Coefficient of thermal expansion test, Enzymatic degradation test and Scanning electron microscopy (SEM), the effect of silk fiber on the structural, thermal and dynamic mechanical properties and enzymatic degradation behavior of the PLA matrix was investigated. As silk fiber was incorporated into PLA matrix, the stiffness of the PLA matrix at higher temperature (70-160 °C) was remarkably enhanced and the dimension stability also was improved, but its thermal stability became poorer. Moreover, the presence of silk fibers also significantly enhanced the enzymatic degradation ability of the PLA matrix. The higher the silk fiber content, the more the weight loss.     

Stabilization of poly(lactic acid) by polycarbodiimide

Polycarbodiimide (CDI) was used to improve the thermal stability of poly(l-lactic acid) (PLA) during processing. The properties of PLA containing various amounts of CDI were characterized by GPC, DSC, rheology, and tensile tests. The results showed that an addition of CDI in an amount of 0.1-0.7 wt% with respect to PLA led to stabilization of PLA at even 210 °C for up to 30 min, as evidenced by much smaller changes in molecular weight, melt viscosity, and tensile strength and elongation compared to the blank PLA samples. In order to examine the possible stabilization mechanism, CDI was reacted with water, acetic acid, l-lactic acid, ethanol and low molecular weight PLA. The molecular structures of the reaction products were measured with FTIR. The results showed that CDI could react with the residual or newly formed moisture and lactic acid, or carboxyl and hydroxyl end groups in the PLA samples, and thus hamper the thermal degradation and hydrolysis of PLA.     

Preparation,characterization, structure‐property relationships,and thermal degradation kinetics of poly (lactic acid)/amidated potassium hydrogen phthalate intercalated layered double hydroxides nanocomposites

A novel nucleating agent, amidated potassium hydrogen phthalate intercalated layered double hydroxides (AP‐LDHs) were prepared using an amidation reaction. Through the structural characterization, it was found that AP‐LDHs had been successfully prepared. Meanwhile, the antibacterial activity of AP‐LDHs was studied. In order to improve the performance of poly (lactic acid) (PLA), PLA/AP‐LDHs nanocomposites were prepared by melt blending. Morphological analysis showed that PLA nanocomposites had an exfoliated structure. Mechanical properties test showed that the mechanical properties of PLA nanocomposites were enhanced. And the fracture scanning electron microscope analysis indicated that the PLA/AP‐LDHs nanocomposites exhibited ductile fracture characteristics. Moreover, differential scanning calorimetry and polarized optical microscopy analysis results demonstrated that the crystallization rate, nucleation density, and crystallinity of PLA/AP‐LDHs were improved. Thermogravimetric analysis and thermal degradation kinetics showed that the thermal stability of the PLA nanocomposites was significantly improved.     

Thermal properties of poly(lactic acid)/organo-montmorillonite nanocomposites

Poly(lactic acid)/organo-montmorillonite nanocomposites were prepared by melt intercalation technique. Maleic anhydride-grafted ethylene propylene rubber (EPMgMA) was added into the PLA/OMMT in order to improve the compatibility and toughness of the nanocomposites. The samples were prepared by single screw extrusion followed by compression molding. The effect of OMMT and EPMgMA on the thermal properties of PLA was studied. The thermal properties of the PLA/OMMT nanocomposites have been investigated by using differential scanning calorimeter (DSC) and thermo-gravimetry analyzer (TG). The melting temperature (T _m), glass transition temperature (T _g), crystallization temperature (T _c), degree of crystallinity (χ_c), and thermal stability of the PLA/OMMT nanocomposites have been studied. It was found that the thermal properties of PLA were greatly influenced by the addition of OMMT and EPMgMA.     

Coarse‐grained A‐graft‐B model of poly(lactic acid) for molecular dynamics simulations

A mesoscopic model of poly(lactic acid) is developed where the polymer is represented as an A‐graft‐B chain with monomer units consisting of two covalently connected beads. A coarse‐graining algorithm is proposed to convert an atomistic model of PLA into a coarse‐grained one. The developed model is based on atomistic simulations of oligolactides to take into account terminal groups correctly. It was used for coarse‐grained simulations of polylactide. Gyration radii and end to end distances of polymer chains as well as the density of the polymer melt are shown to be in a good agreement with those obtained from atomistic simulations. The thermal expansion coefficients of the OLA melts calculated using the coarse‐grained model are in reasonable agreement with those obtained from all‐atom molecular dynamics. The model provides a 17‐fold speedup compared with atomistic calculations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 604–612     

Synthesis,characterization of layered double hydroxide‐poly(methylmethacrylate) graft copolymers via activators regenerated by electron transfer for atom transfer radical polymerization and its effect on the performance of poly(lactic acid)

Layered double hydroxide‐poly(methylmethacrylate) (LDH‐PMMA) graft copolymers were prepared via activators regenerated by electron transfer for atom transfer radical polymerization. The results showed that the hydrophobicity of LDH‐PMMA was improved by the incorporation of hydrophilic groups. Moreover, poly(lactic acid) (PLA)/LDH‐PMMA nanocomposites were prepared by melt blending to enhance the performances of PLA. The crystallization and mechanical properties of the PLA/LDH‐PMMA nanocomposites were studied by differential scanning calorimetry, tensile testing, and polarized optical microscopy, respectively. Results of mechanical testing showed that the tensile strength, elongation at break, and impact strength of PLA/LDH‐PMMA nanocomposites were increased by 5.64%, 37.95%, and 49.70%, respectively, compared with PLA. The differential scanning calorimetry results indicated that LDH‐PMMA eliminated the cold crystallization of PLA matrix and improved the crystallinity of PLA by 37.26%. The polarized optical microscopy of PLA/LDH‐PMMA nanocomposites demonstrated that LDH‐PMMA increased the crystallization rate of PLA. It was also found that the rheological behaviors of the PLA nanocomposites were significantly enhanced. Based on these results, a new choice for modified LDHs was provided and used as a nucleating agent to improve the properties of PLA.     

Morphological changes during heating in poly(L‐lactic acid)/poly(butylene succinate) blend systems as studied by synchrotron X‐ray scattering

Blends of poly(L ‐lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared in various compositions via melt mixing, and the morphological changes were investigated with differential scanning calorimetry and synchrotron wide‐angle and small‐angle X‐ray scattering techniques at a heating rate of 10 °C/min. Differential scanning calorimetry thermograms of PLA/PBS blends showed two distinct melting peaks over the entire composition range. The exothermal peak for PLA shifted significantly to a lower temperature and overlapped with that of PBS around 100 °C. A depression of the melting point of the PLA component via blending was observed. The synchrotron wide‐angle X‐ray scattering during heating revealed that there was no cocrystallization or crystal modification via blending. The synchrotron small‐angle X‐ray scattering data showed that well‐defined double‐scattering peaks (or peaks with a clear scattering shoulder) appeared during crystallization, indicating that this system possessed dual lamellar stacks. These peaks were deconvoluted into two components with a peak separation computer program, and then the morphological parameters of each component were obtained by means of the correlation function. The long period and average lamellar thickness of the two components before melting decreased with an increasing content of the other polymer component. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1931–1939, 2002