Biodegradability of nonwoven flax fiber reinforced polylactic acid biocomposites

Biocomposites of flax reinforced polylactic acid (PLA) were made using a new technique incorporating an air‐laying nonwoven process. PLA and flax fibers were mixed and converted to the webs in the air‐laying process. Prepregs were then made from the fiber webs by thermal consolidation. The prepregs were finally converted to composites by compression molding. This study was investigated the biodegradability and water absorption properties of the composites. The composites were incubated in compost under controlled conditions. The percentage weight loss and the reduction in mechanical properties of PLA and biocomposites were determined at different time intervals. It was found that with increasing flax content, the mechanical properties of the biocomposites decreased more during the burial trial. The increasing of flax content led to the acceleration of weight loss due to preferential degradation of flax. This was further confirmed by the surface morphology of the biodegraded composites from scanning electron microscope image analysis. Morphological observations indicated severe disruption of biocomposites structure between 60 and 120 days of incubation. POLYM. COMPOS., 35:2094–2102, 2014. © 2014 Society of Plastics Engineers     

Three‐dimensional nonwoven flax fiber reinforced polylactic acid biocomposites

Three‐dimensional (3D) shell‐structured PLA/Flax biocomposites were fabricated using a novel method incorporating the 3D nonwoven web‐forming process. PLA and flax fibers were blended in the fiber opening stage and converted to webs on the 3D mold using the air‐laying principle. The 3D webs were then consolidated by through‐air thermal bonding. The compression molding technique was used finally to convert the 3D webs to the biocomposites. The relationship between the main process parameters and the properties of the biocomposites was investigated. The results show that with increasing flax fiber content, the crush failure load, total energy absorption, specific energy absorption, and crush efficiency increased. The crushing properties decreased with increased molding temperature, but the crushing properties are not significantly affected by the molding time. The physical properties of 3D biocomposites were also evaluated and the appropriate processing parameters for 3D biocomposites were established. POLYM. COMPOS., 35:1244–1252, 2014. © 2013 Society of Plastics Engineers     

Fabrication and characterization of dental mirror product using polylactic acid biocomposites

Polylactic acid biocomposites were prepared by mixing castor oil and talc by melt blending using twin-screw extruder. The amount of talc and castor oil was fixed at 20 and 1?wt%, respectively. The biocomposites were analyzed using Fourier transform infrared spectroscopy, impact strength, bioactivity, cytotoxicity, and soil burial tests. Using biocomposites, mouth mirror product was fabricated for oral dental application using injection molding machine. The impact strength of biocomposites increases by 56% than neat polylactic acid. Bioactivity and cytotoxicity tests of the biocomposites prove that they have no toxicity and the product can be used for oral dental application.     

Properties of kenaf fiber/polylactic acid biocomposites plasticized with polyethylene glycol

Biocomposites of kenaf fiber (KF) and polylactic acid (PLA) were prepared by an internal mixer and compression molding. PLA was plasticized with polyethylene glycol (PEG) (10 wt%) and evaluated as the polymer matrix (p‐PLA). Fiber loadings were varied between 0 and 40 wt%. The tensile, dynamic mechanical, and morphological properties and water absorption behavior of these composites were studied. Reinforcing effect of KF was observed when fiber loading exceeded 10 wt% despite of the inferior fiber‐matrix adhesion observed via scanning electron microscopy (SEM). Un‐plasticized PLA/KF composite exhibited higher tensile properties than its plasticized counterpart. Fiber breakage and heavily coated short pulled‐out of fibers were observed from the SEM micrographs of the composite. The presence of PEG might have disturbed the fiber‐matrix interaction between KF and PLA in the plasticized composites. Addition of PEG slightly improved the un‐notched impact strength of the composites. Dynamic mechanical analysis showed that the storage and loss moduli of p‐PLA/KF composites increased with the increase in fiber loading due to increasing restrictions to mobility of the polymer molecules. The tan delta of the composites in contrast showed an opposite trend. p‐PLA and p‐PLA/KF composites exhibited non‐Fickian behavior of water absorption. SEM examination revealed microcracks on p‐PLA and p‐PLA/KF surfaces. POLYM. COMPOS., 31:1213–1222, 2010. © 2009 Society of Plastics Engineers     

Effect of flax fiber content on polylactic acid (PLA) crystallization in PLA/flax fiber composites

Crystallization of polylactic acid (PLA) has a profound effect on its thermal stability and mechanical properties. However, almost no crystallization occurs in actual injection molding process due to rapid cooling program. In this paper, flax fiber was employed as nucleator to enhance the crystallization capability of PLA. Effects of flax fiber content on cold crystallization, melt crystallization, crystallinity, crystal form, morphologies, and size of spherulites of PLA/flax fiber composites were investigated. Dynamic mechanical analysis was innovatively employed to study cold crystallization temperature of PLA/flax fiber composites under dynamic force, and the relationship between cold crystallization temperature (y) and flax fiber content (x) data was fitted by the function y = 34.1 × exp (?x/5.7) + 78.0. The differential scanning calorimetry results showed that the cold crystallization temperature of composites dropped, the melt crystallization temperature of composites increased, and the crystallinity of composites improved with increasing of flax fiber content. Using polarized optical microscopy, it has been found that the spherocrystal size of composites was much smaller than that of neat PLA, and flax fiber induced transcrystallization on the flax fiber surfaces. Wide-angle X-ray diffraction was applied to reveal that flax fiber significantly enhanced the formation of α-form PLA crystals.     

Properties of silanized nypa fruticans filled polylactic acid/recycled low density polyethylene biocomposites

The biocomposites of Nypa Fruticans (NF) and Polylactic acid (PLA)/recycled low density polyethylene (rLDPE) were prepared using Brabender EC PLUS. The effect of NF content and silane coupling agent on mechanical, thermal, and morphological properties were studied. The results show that addition of NF in PLA/rLDPE biocomposites have decreased the tensile strength, elongation at break, and crystallinity of biocomposites. The Young's modulus of biocomposites and thermal stability increased with the increasing NF content. The surface of NF fillers were silanized to improved the interfacial adhesion between the NF filler and PLA/rLDPE matrix. It was found that the tensile strength, Young's modulus, crystallinity of PLA, and thermal stability of silanized biocomposites higher as compared to untreated biocomposites. The enhancement of the properties of biocomposites with silane treatment was proven by SEM studied. The silanized biocomposites showed better interfacial interaction and adhesion between NF and PLA/rLDPE matrix. POLYM. ENG. SCI., 55:1733–1740, 2015. © 2014 Society of Plastics Engineers     

Effect of partial replacement of chitosan with halloysite nanotubes on the properties of polylactic acid hybrid biocomposites

In this study, hybrid chitosan/halloysite nanotubes (Cs/HNTs) reinforced polylactic acid (PLA) were prepared via melt compounding and compression molding techniques. In the fabrication of PLA/Cs/HNTs hybrid biocomposites, the partial replacement of Cs with HNTs was performed at filler loading of 2.5 parts per hundred parts of polymer (php), proceeding from the highest tensile strength of PLA/Cs obtained in our previous study. Cs was partially replaced with different HNTs loadings (0.5, 1, 1.5, 2, and 2.5) php and its effects on the functional group, thermal, tensile, morphological, and water absorption properties were investigated systematically. The results revealed that the combined loading of 1 php Cs and 1.5 php HNTs hybrid fillers into PLA showed the best performance in all properties. Fourier transform infrared spectroscopy (FTIR) analysis indicated that the siloxane (Si O) group of HNTs had chemically interacted with the amine group of Cs. The thermal analysis demonstrated that partial replacement of Cs with 1.5 php HNTs improved the thermal stability of PLA/2.5Cs/0HNTs biocomposite by ~12%. Yet, the percentage of crystallinity (χ_c) reduced with HNTs addition due to the phase adhesion improvement. Moreover, PLA/1Cs/1.5HNTs hybrid biocomposites showed the highest tensile strength and elongation at break of 59 MPa and 2.72%, respectively. This correlated with the uniform dispersion and better interfacial adhesion between Cs/HNTs fillers in the PLA matrix, as confirmed by the field emission scanning electron microscopy (FESEM). In addition, partial replacement of Cs with HNTs exhibited a lower water absorption percentage, which suggested the advantage of hybrid fillers to reduce water uptake, and is beneficial in a wide range of applications.     

Fabrication and mechanical analysis of mimosa tannin and commercial flax fibers biocomposites

Composites were prepared by impregnating commercial nonwoven and unidirectional flax fibers mats, with a mimosa tannin/hexamine resin without addition of NaOH as it was described in previous papers and with improved results. The influence of various parameters was observed: the curing cycle including temperature, time, pressure, the moisture content, and the number of fiber mats the composites were made of. A new two-step method was investigated: full drying of the pre-impregnated mats for storage first and then rehydratation just before pressing. The composites obtained gave good modulus of elasticity and tensile strength in traction as well as a good resistance to water swelling for composites prepared with 50% matrix resin/50% natural fibers. Best results appear to be obtained using a slow curing at low temperature (130?°C for 35?min) with moisture content of 20% on dry material.     

Effect of peanut shell content on mechanical,thermal, and biodegradable properties of peanut shell/polylactic acid biocomposites

Peanut shell (PNS) was combined with polylactic acid (PLA) to form biocomposites. The biocomposites, with up to 40 wt% PNS, were prepared using a twin–screw extruder. The effect of PNS content on the thermal, mechanical, thermomechanical, morphological, and biodegradable properties was studied. The results showed that the addition of PNS caused a reduction of the melting temperature and the decomposition temperature. Furthermore, the crystallinity of the biocomposites slightly increased with increasing PNS up to 30 wt%. The morphological study showed poor interfacial adhesion between the PNS and PLA matrix. Nevertheless, the mechanical properties revealed that the maximum tensile strength and Young's modulus were at a 30 wt% PNS loading and decreased as more PNS was incorporated into the PLA matrix. The impact strength decreased with an increase in PNS content. The addition of PNS showed significantly improvement of the storage modulus of PLA at high temperature (>80°C). Moreover, the presence of PNS enhanced the biodegradability of the biocomposites. POLYM. COMPOS., 38:682–690, 2017. © 2015 Society of Plastics Engineers     

Mechanical and thermal properties of coconut shell powder filled polylactic acid biocomposites: effects of the filler content and silane coupling agent

The effects of the filler content and the coupling agent 3-aminopropyltriethoxysilane (3-APE) on the mechanical properties, thermal properties, and morphologies of polylactic acid (PLA)/coconut shell powder (CSP) biocomposites were investigated. It was found that increasing the CSP content decreased the tensile strengths and elongations at break of the PLA/CSP biocomposites. However, incorporating CSP increased their modulus of elasticity. The tensile strengths and modulus of elasticity of the PLA/CSP biocomposites were enhanced by the presence of 3-APE, which can be attributed to a stronger filler–matrix interaction. The thermal stabilities of the biocomposites increased with the filler content, and they were enhanced by 3-APE treatment. Meanwhile, the presence of CSP increased the glass transition temperatures (T _g) and crystallinities (X _c) of the PLA/CSP biocomposites at a filler content of 30 php. After 3-APE treatment, T _g and X _c of the PLA/CSP biocomposites increased due to enhanced interfacial bonding. The presence of a peak crystallization temperature (T _c) for the PLA/CSP biocomposites indicated that the CSP has a nucleating effect. The melting temperatures (T _m) and the T _c values of the biocomposites were not significantly affected by the filler content and 3-APE. PLA/CSP biocomposites that had been treated with 3-APE presented the strongest filler–matrix interaction, as confirmed by SEM.     

Mechanical properties of surface‐treated banana fiber/polylactic acid biocomposites: A comparative study of theoretical and experimental values

Current study evaluates the effect of fiber surface treatments on the mechanical properties of banana fiber (BF) reinforced polylactic acid (PLA) biocomposites. Experimental results indicate increase in tensile modulus and strength upon surface treatments of BF with various silanes (APS and Si69) and NaOH. Approximately, an increase of 136% in tensile strength and 49% in impact strength was obtained in case of biocomposites with Si69‐treated BF compared with the untreated BF biocomposites. Also, experimentally determined mechanical modulus of untreated and surface‐treated BF biocomposite has been compared with the mechanical modulus calculated using various micromechanical models. Models such as Hirsch's, modified Bawyer and Bader's, and Brodnyan model showed good agreement with the experimentally determined results. Similarly, other models like Halpin‐Tsai, Nielson modified Halpin‐Tsai, and Cox's model also have been tried for the comparative study with the experimental data. Surface modification of BF showed increased interfacial adhesion between the fiber and the matrix which was evident from lowered difference between the experimentally and theoretically derived mechanical modulus. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

聚乳酸的合成和应用

作为新型环保材料,聚乳酸的应用日益受到人们的重视。简要介绍了聚乳酸的合成方法和应用领域,提出合成中亟待解决的问题,对其未来的发展作了展望。     

Effect of core–shell acrylate rubber particles on the thermomechanical and physical properties of biocomposites from polylactic acid and olive solid waste

Biocomposites from polylactic acid (PLA) and olive solid waste (OSW) were melt‐blended with core–shell acrylate rubber particles (ACR) in order to enhance the thermal stability upon melt processing and the mechanical performances of these biocomposites, thereby expanding their area of application. Dynamic mechanical analysis indicated that the ACR particles imparted more flexibility to the PLA/OSW biocomposites and thermal analysis showed that the incorporation of ACR significantly restrained the ability of the PLA chains to crystallize. The values of complex viscosity and storage modulus were significantly increased with the introduction of ACR. These results could be assigned to the entanglements between the PLA chains and those of the ACR shell, giving rise to a physical network that limited the segmental mobility of PLA and induced a high melt elasticity. Mechanical tests revealed that the elongation at break and the impact strength of the biocomposites were considerably improved. Moreover, morphological observations showed a clear adhesion enhancement between the PLA matrix and the OSW fillers in the presence of the ACR additive. POLYM. ENG. SCI., 58:894–902, 2018. © 2017 Society of Plastics Engineers     

聚乳酸微球的制备

以L-乳酸为原料,锡粒为催化剂,实现了丙交酯的开环聚合反应,红外光谱结果表明,合成了分子量可控的聚乳酸。以二氯甲烷为溶剂,聚乙烯醇为表面活性剂,制备了聚乳酸微球,研究了聚乙烯醇浓度对聚乳酸微球的影响。结果表明,当聚乙烯醇浓度增加时,微球半径变小,但粒径分布均匀度下降,聚乙烯醇浓度为1%时,聚乳酸成球效果较好。     

聚乳酸的间接合成研究

以D,L乳酸为原料、ZnO为催化剂,制备中间体丙交酯;再以丙交酯为原料、ZnO为催化剂,开环制得了较高相对分子质量的聚乳酸。用红外光谱仪(IR)对丙交酯及聚乳酸进行了表征,并讨论了影响丙交酯产率、聚乳酸相对分子质量的主要因素。得出在压力1.7×104Pa、催化剂质量分数为2.2%的条件下,两步脱水后制得的丙交酯经多次纯化后,其最大产率可达31%。在压力1.7×104Pa、催化剂质量分数0.06%时,可得到相对分子质量为1.1×105的聚乳酸。     

聚乳酸合成和改性

介绍了聚乳酸的合成工艺一步法、两步法及其改进,通过分析聚乳酸自身存在的特性及局限性,介绍了近几年聚乳酸的改性发展,包括耐热性的改性,亲水性改性以及机械性能方面的改性。     

Effect of coupling agent on polylactic acid/polypropylene and polylactic acid/polyamide 6 foam composites

The main part of polymer materials generated from fossil fuels do not degrade after completing their usage life and then begin to be waste in the environment. This situation has led to the emphasis on environmentally friendly, biodegradable, and bio-based polymers obtained from renewable sources as an alternative. In recent years, several studies are concentrated on especially lightweight and carbon dioxide (CO₂) emission limitations. In this work, the goal was to investigate at the same time environmentally friendly and lightweight polymer foam composites based on polylactic acid (PLA) polymer without lowering the performances of the materials. In this aim, polymer foam composites containing polypropylene (PP), polyamide 6 (PA6) and PLA were produced (PLA/PA6 (30:70) and PLA/PP (30:70)) with a chemical blowing agent (CBA) introduced at 1.5 wt.% to the polymer mixture. To improve the interpolymer compatibility and foaming activity maleic anhydride-grafted polylactic acid (PLA-g-MA) was utilized as coupling agent (CA) in different ratios (1, 3 and 5 wt.%). From the evaluation of the polymer mixtures in terms of their lightness, thermal and mechanical strength, the most appropriate CA ratios were determined as 1 wt.% for foamed PLA/PP (30:70) mixtures and 3 wt.% for foamed PLA/PA6 (30:70) mixtures.     

Halloysite nanotube reinforced polylactic acid composite

Polylactic acid (PLA) has a long history in medical applications. Reinforced PLA has the potential to be used in the medical applications that require high mechanical strength such as coronary stents and bone fixation devices. Halloysite nanotube (HNT) has received considerable attention recently due to its tubular structure, high aspect ratio, high mechanical strength, thermal stability, biocompatibility and sustained drug releasing properties. Halloysite has been investigated in compounding with many polymers. However, the research in compounding halloysite with biodegradable materials for use in biological applications is sparse. In this study various weight fractions of HNT was compounded with the biodegradable polymer PLA using a melt compounding method. Tensile test, Fourier infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), contact angle test, scanning electron microscopy (SEM), void content and thermogravimetric analysis (TGA) were carried out to study the PLA/HNT composite. Tensile test results indicated that Young's modulus and stiffness of PLA were enhanced with the addition of HNT; FTIR spectra showed the interaction between the PLA and HNT; whereas contact angle measurements indicated that the wettability of the PLA/HNT composite was not affected by the addition of HNT. However, the thermal stability of PLA was adversely effected by the addition of HNT which may be related to the presence of voids between the polymer and matrix. Nevertheless, the reinforced PLA/HNT composite, which maintains the surface characteristics, may prove beneficial for use in biological applications. POLYM. COMPOS., 38:2166–2173, 2017. © 2015 Society of Plastics Engineers     

聚乳酸合成技术研究进展

聚乳酸因可生物降解、性能优异、应用广泛而深受青睐。本文介绍了2种主要化学合成聚乳酸的方法：丙交酯开环聚合法和乳酸直接缩聚法。分析了这2种方法的优势和缺陷：丙交酯开环聚合法设备简单,可得到大分子量的聚乳酸,缺点是成本较高,整个工艺复杂,路线长;乳酸直接缩聚法原料乳酸来源充足,价格便宜,单体转化率较高,工艺简单,不需要经过中间体的纯化,因而成本较低,缺陷是较难得到高分子量的聚合物。文中指出积极开展聚乳酸的合成工艺研发、进一步降低生产成本是当前聚乳酸研究的重要课题,重点在于简单易行的高分子量聚乳酸合成工艺的突破。