Novel toughened polylactic acid nanocomposite: Mechanical,thermal and morphological properties

The objective of the study is to develop a novel toughened polylactic acid (PLA) nanocomposite. The effects of linear low density polyethylene (LLDPE) and organophilic modified montmorillonite (MMT) on mechanical, thermal and morphological properties of PLA were investigated. LLDPE toughened PLA nanocomposites consisting of PLA/LLDPE blends, of composition 100/0 and 90/10 with MMT content of 2 phr and 4 phr were prepared. The Young’s and flexural modulus improved with increasing content of MMT indicating that MMT is effective in increasing stiffness of LLDPE toughened PLA nanocomposite even at low content. LLDPE improved the impact strength of PLA nanocomposites with a sacrifice of tensile and flexural strength. The tensile and flexural strength also decreased with increasing content of MMT in PLA/LLDPE nanocomposites. The impact strength and elongation at break of LLDPE toughened PLA nanocomposites also declined steadily with increasing loadings of MMT. The crystallization temperature and glass transition temperature dropped gradually while the thermal stability of PLA improved with addition of MMT in PLA/LLDPE nanocomposites. The storage modulus of PLA/LLDPE nanocomposites below glass transition temperature increased with increasing content of MMT. X-ray diffraction and transmission electron microscope studies revealed that an intercalated LLDPE toughened PLA nanocomposite was successfully prepared at 2 phr MMT content.     

Isothermal crystallization behavior and mechanical properties of polylactide/carbon nanotube nanocomposites

Carbon nanotube (CNT)–reinforced polylactide (PLA) nanocomposites were prepared using a melt compounding process employing a twin-screw extruder. The isothermal crystallization kinetics of PLA/CNT nanocomposites according to Avrami’s theory were analyzed using differential scanning calorimetry in the temperature range 90–120 °C. There was a significant dependence of CNT on the crystallization behavior of the PLA matrix. The incorporation of CNT improved effectively the crystallization rate of PLA/CNT nanocomposites through heterogeneous nucleation. The nucleating effect of CNTs which increased the number of nucleation sites and decreased the average spherulite size was confirmed using polarized optical microscopy. The rheological properties of the PLA/CNT nanocomposites were also investigated. Changes in the microstructure of the PLA/CNT nanocomposites occurred by incorporating CNT. Furthermore, the tensile strength/modulus and thermal stability of PLA/CNT nanocomposites were enhanced when a very small quantity of CNT was added. This research accounts for the effect of CNTs, which significantly influenced the isothermal behavior, thermal stability, mechanical, and rheological properties of the PLA/CNT nanocomposites, providing a design guide for PLA/CNT nanocomposites in industrial fields.     

Nanodiamond/poly (lactic acid) nanocomposites: Effect of nanodiamond on structure and properties of poly (lactic acid)

Nanodiamond (ND)/poly (lactic acid) (PLA) nanocomposites with potential for biological and biomedical applications were prepared by using melting compound methods. By means of transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analyses (TGA), Dynamic mechanical analyses (DMA), Differential scanning calorimetry (DSC) and Tensile test, the ND/PLA nanocomposites were investigated, and thus the effect of ND on the structural, thermal and mechanical properties of polymer matrix was demonstrated for the first time. Experimental results showed that the mechanical properties and thermal stability of PLA matrix were significantly improved, as ND was incorporated into the PLA matrix. For example, the storage modulus (E′) of 3 wt% ND/PLA nanocomposites was 0.7 GPa at 130 °C which was 75% higher than that of neat PLA, and the initial thermal decomposition was delayed 10.1 °C for 1 wt% ND/PLA nanocomposites compared with the neat PLA. These improvements could be ascribed to the outstanding physical properties of ND, homogeneous dispersion of ND nanoclusters, unique ND bridge morphology and good adhesion between PLA matrix and ND in the ND/PLA nanocomposites.     

Plasticized polylactic acid nanocomposite films with cellulose and chitin nanocrystals prepared using extrusion and compression molding with two cooling rates: Effects on mechanical,thermal and optical properties

Triacetate citrate plasticized poly lactic acid and its nanocomposites based on cellulose nanocrystals (CNC) and chitin nanocrystals (ChNC) were prepared using a twin-screw extruder. The materials were compression molded to films using two different cooling rates. The cooling rates and the addition of nanocrystals (1 wt%) had an impact on the crystallinity as well as the optical, thermal and mechanical properties of the films. The fast cooling resulted in more amorphous materials, increased transparency and elongation to break, (approx. 300%) when compared with slow cooling. Chitin nanocomposites were more transparent than cellulose nanocomposites; however, microscopy study showed presence of agglomerations in both materials. The mechanical properties of the plasticized PLA were improved with the addition of a small amount of nanocrystals resulting in PLA nanocomposites, which will be further evaluated for film blowing and thus packaging applications.     

Effect of nanoclays on physico-mechanical properties and adhesion of polyester-based polyurethane nanocomposites: structure–property correlations

Polyester–polyurethane nanocomposites based on unmodified and modified montmorillonite clays were compared in terms of their morphology, mechanical, thermal, and adhesive properties. Excellent dispersion of the modified nanoclay in polymer with 3 wt% loading was confirmed from X-ray diffraction, and low-, and high-magnification transmission electron micrographs. The properties of the clay-reinforced polyurethane nanocomposites were a function of nature and the content of clay in the matrix. The nanocomposite containing 3 wt% modified clay exhibits excellent improvement in tensile strength (by ~100%), thermal stability (20 °C higher), storage modulus at 25 °C (by ~135%), and adhesive properties (by ~300%) over the pristine polyurethane.     

亚麻纤维增强聚乳酸可降解复合材料的制备与性能

将制浆造纸用亚麻短纤维与聚乳酸(PLA)熔融共混,用注塑方法成型亚麻纤维/聚乳酸复合材料试样。通过差示扫描量热实验(DSC)、动态力学性能测试(DMA)、热重分析(TGA)和力学性能测试等方法,研究了聚乳酸和亚麻纤维在不同质量配比下,复合材料热性能、动态力学性能和力学性能的变化规律。随着亚麻纤维的加入,复合材料的结晶度增大,热稳定性增强,储能模量得到提高,力学性能也有了明显变化:纤维含量为20%时,拉伸强度为45.88 MPa,比纯PLA的增加了21%;同时,弯曲模量的增幅达到30%。     

The effect of crystallization of PLA on the thermal and mechanical properties of microfibrillated cellulose-reinforced PLA composites

This paper describes the thermal and mechanical properties of nanocomposites based on polylactic acid (PLA) and microfibrillated cellulose (MFC). The primary objective of this study was to improve the storage modulus of PLA at a high temperature. MFC and PLA were mixed in an organic solvent with various fiber contents up to 20 wt%, followed by drying, kneading and hot pressing into sheets. The nanocomposites were prepared in two different states, fully amorphous and crystallized. Differential scanning calorimetry (DSC) measurements revealed that the presence of MFC accelerates the crystallization of PLA. The tensile modulus and strength of neat PLA were improved with an increase of MFC content in both amorphous and crystallized states. The addition of 20 wt% of MFC in PLA improved the storage modulus of crystallized PLA at a high temperature (120 °C) from 293 MPa to 1034 MPa.     

Preparation,optical and thermal properties of CdSe–ZnS/poly(lactic acid) (PLA) nanocomposites

In this study, CdSe–ZnS/poly(lactic acid) (PLA) nanocomposite films, containing different concentrations of surface-modified CdSe–ZnS quantum dots (QDs), were prepared via a solution casting method. The optical microstructural and thermal properties of the as-prepared QDs/PLA films were investigated. The QDs/PLA films exhibited strong and stable photoluminescence (PL) intensity with concentration dependent amplitudes. The transmission electron microscopy (TEM) pictures revealed that QDs of ∼5 nm diameter were uniformly dispersed in the PLA matrix. According to the results of thermogravimetric analysis, the weight-loss onset temperature of PLA clearly decreased with the QD content. A combination of Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) results suggested that the QDs exhibit obvious nucleation activity on the crystallization behavior of the PLA matrix. This research provides useful information to the foundations of practical applications of QDs/PLA nanocomposites as fluorescent and biodegradable functionalized materials.     

Effects of modified Clay on the morphology and thermal stability of PMMA/clay nanocomposites

The potential to improve the mechanical, thermal, and optical properties of poly(methyl methacrylate) (PMMA)/clay nanocomposites prepared with clay containing an organic modifier was investigated. Pristine sodium montmorillonite clay was modified using cocoamphodipropionate, which absorbs UVB in the 280–320 nm range, via ion exchange to enhance the compatibility between the clay platelets and the methyl methacrylate polymer matrix. PMMA/clay nanocomposites were synthesized via in situ free-radical polymerization. Three types of clay with various cation-exchange capacities (CEC) were used as inorganic layered materials in these organic–inorganic hybrid nanocomposites: CL42, CL120, and CL88 with CEC values of 116, 168, and 200 meq/100 g of clay, respectively. We characterized the effects of the organoclay dispersion on UV resistance, effectiveness as an O₂ gas barrier, thermal stability, and mechanical properties of PMMA/clay nanocomposites. Gas permeability analysis demonstrated the excellent gas barrier properties of the nanocomposites, consistent with the intercalated or exfoliated morphologies observed. The optical properties were assessed using UV–Visible spectroscopy, which revealed that these materials have good optical clarity, UV resistance, and scratch resistance. The effect of the dispersion capability of organoclay on the thermal properties of PMMA/clay nanocomposites was investigated by thermogravimetric analysis and differential scanning calorimetry; these analyses revealed excellent thermal stability of some of the modified clay nanocomposites.     

Characteristics of nanoclay and calcined nanoclay-cement nanocomposites

The influence of nanoclay (NC) and calcined nanoclay (CNC) on the mechanical and thermal properties of cement nano-composites presented. Calcined nanoclay is prepared by heating nanoclay (Cloisite 30B) at 900 °C for 2 h. Characterisation of microstructure is investigated using Quantitative X-ray Diffraction Analysis (QXDA) and High Resolution Transmission Electron Microscopy (HRTEM). Estimation of Ca(OH)₂ content in the cement nanocomposite is studied by the combination of QXDA and thermogravimetry analysis (TGA) techniques. Results showed that the mechanical and thermal properties of the cement nanocomposites are improved as a result of NC and CNC addition. An optimum replacement of ordinary Portland cement with 1 wt% CNC is observed through reduced porosity and water absorption as well as increased density, compressive strength, flexural strength, fracture toughness, impact strength, hardness and thermal stability of cement nanocomposites. The microstructural analyses from QXRA and SEM indicate that the CNC acted not only as a filler to improve the microstructure, but also as the activator to support the pozzolanic reaction. Cost-benefit analysis indicates that nanoparticles are expensive but from economic point of view nanoclay is used in very small amount (i.e. 1 wt. %) in cementitious materials. As a result nanoclay does not add any significant cost but improves the mechanical properties significantly.     

可生物降解性聚合物-层状硅酸盐纳米复合材料的研究进展

可生物降解性聚合物一层状硅酸盐纳米复合材料比聚合物基体有更好的力学强度、热稳定性、热变形温度、气体阻隔特性和更快的降解速率，表现出剪切变稀、模量升高、似固体行为等流变特性。文中综述了可生物降解性聚合物纳米复合材料的制备方法、表征手段、性能测试及其应用等方面的研究进展。     

Mechanical and thermal properties of chicken feather fiber/PLA green composites

Chicken feather fiber (CFF)/reinforced poly(lactic acid) (PLA) composites were processed using a twin-screw extruder and an injection molder. The tensile moduli of CFF/PLA composites with different CFF content (2, 5, 8 and 10 wt%) were found to be higher than that of pure PLA, and a maximum value of 4.2 GPa (16%↑) was attained with 5 wt% of CFF without causing any substantial weight increment. The morphology, evaluated by scanning electron microscopy (SEM), indicated that an uniform dispersion of CFF in the PLA matrix existed. The mechanical and thermal properties of pure PLA and CFF/PLA composites were compared using dynamic mechanical analysis (DMA), thermomechanical analysis (TMA) and thermogravimetric analysis (TGA). DMA results revealed that the storage modulus of the composites increased with respect to the pure polymer, whereas the mechanical loss factor (tan δ) decreased. The results of TGA experiments indicated that the addition of CFF enhanced the thermal stability of the composites as compared to pure PLA. The outcome obtained from this study is believed to assist the development of environmentally-friendly composites from biodegradable polymers, especially for converting agricultural waste – chicken feather into useful products.     

Improvement on the properties of polylactic acid (PLA) using bamboo charcoal particles

Bamboo charcoal (BC) derived from bamboo plants is one kind of well recognized multi-functional materials which has been used in various applications such as medical, cosmetic, food processing and health-related products. In this paper, BC particle is used as reinforcement for polylactic acid (PLA) to enhance its mechanical, thermal and optical properties. The comparison on tensile, flexural and impact properties of BC particle reinforced PLA composites (BC/PLA composites) with the content ranging from 2.5 to 10 wt.% is conducted. Experimental results indicated that the maximum tensile strength, flexural strength and ductility index (DI) of BC/PLA composites increased by 43%, 99% and 52%, respectively as compared with those of neat PLA. This phenomenon was attributed to the uniform distribution of high aspect ratio and surface area of BC particles. Further increasing the BC content to 7.5 wt.% would decrease the glass transition temperature of BC/PLA composites. The mechanical properties of BC/PLA composites were reduced as compared with a neat PLA sample when they were exposed to compost degradation. However, less reduction in these properties was found when they were subject to UV irradiation. UV–Vis spectrometer analysis supported the results of UV irradiation. Fracture surfaces of tensile test samples with and without compost degradation or UV irradiation were analysed by using scanning electron microscopy (SEM). SEM images revealed that there was a good BC particle dispersion in the composites through extrusion and injection moulding processes if the particle content was below 7.5 wt.%.     

PLA/I.34TCN纳米复合材料的制备及其性能研究

将改性纳米黏土I.34TCN与聚乳酸(PLA)经过二次熔融混合制备了PLA/I.34TCN纳米复合材料。TEM表征结果显示,较高的黏土剥离程度提高了黏土在PLA中的分散性,使两相之间的界面作用力增强,同时可以使两相之间具有较大的界面增塑区;DSC表征结果显示,剥离型纳米黏土对纳米复合材料起到了结晶成核剂的作用,提高了纳米复合材料的结晶度。上述两方面的原因综合改善了纳米复合材料的力学性能,当黏土质量分数为2%时,PLA/I.34TCN纳米复合材料中黏土的剥离程度最高,使得该纳米复合材料的断裂伸长率显著提高,最多可提高101.00%,是纯PLA的18倍。TG表征结果发现,纳米复合材料的热稳定性能随I.34TCN含量的增加而逐渐增加。     

聚乳酸/酯化纤维素纳米晶体共混膜性能研究

以聚乳酸（PLA）为基体,酯化纤维素纳米晶体（ECNC）为添加剂,制备了PLA/ ECNC共混膜。探讨了原始纤维素纳米晶体（CNC）与ECNC对PLA膜的透光率、表面形貌、热稳定性、亲疏水性及力学性能的影响。结果表明,与CNC相比,ECNC与PLA的相容性提高,透光率、热稳定性及力学性能也显著增强;经酯化的纤维素纳米晶体能降低CNC的亲水性,从而增强与PLA的界面黏合力,使CNC在PLA共混膜中的质量分数由小于1%提高到5%。该PLA/ECNC共混膜在包装塑料领域具有潜力,为制备出性能更加优良的可降解包装用塑料提供了一种简单可行的方法。     

Structure and properties of novel electrospun tussah silk fibroin/poly(lactic acid) composite nanofibers

The tussah silk fibroin (TSF)/poly(lactic acid) (PLA) composite nanofibers with different composition ratios were prepared by electrospinning with 1,1,1,3,3,3-Hexafluoro-2-propanol as the solvent. The morphology and secondary structure of the fibers were characterized by Scanning electronic microscope, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The thermal and mechanical tests were also performed. The spinnability of TSF solution was improved significantly through adding 10% PLA, and the average diameter of the fibers decreased from 583 nm to 178 nm with an obvious improvement in fiber diameter uniformity. In addition, the mechanical properties of electrospun nanofibers increased evidently after blending 10% PLA, whereas the thermal properties kept stable. FTIR and XRD analysis indicated the addition of 5% PLA could induce a conformation transformation of TSF from random coil and α-helix to β-sheet, however, when PLA content was more than 10%, the β-sheet structure of TSF in composite nanofibers decreased, and the phase separation of two compositions occurred. Therefore, when PLA content exceeded 15%, the average diameters of TSF/PLA composite nanofibers increased and appeared to be polarized, moreover, the mechanical properties of the fibers decreased with the increase of PLA content, and the fibers displayed the mechanical behavior of PLA component more.     

改性二氧化硅对SiO2/PLA复合膜性能的影响

目的研究改性二氧化硅对聚乳酸力学性能、氧气透过性能和水蒸气透过性能的影响。方法选择粒径为50nm的工业级二氧化硅为添加剂,使用KH570硅烷偶联剂对其进行改性,然后通过溶液浇铸法将改性后的二氧化硅与聚乳酸共混制备成膜。测试分析拉伸性能、透氧性能和透水蒸气性能,表征复合膜的力学性和阻隔性能。结果与纯PLA膜相比,改性复合膜的拉伸强度和弹性模量分别提高了18.65%和19.91%;玻璃化转变温度比纯PLA膜高11℃左右,热稳定性得到增强。与纯PLA膜相比,改性复合膜的氧气透过系数和水蒸气透过系数分别降低了29.89%和43.76%,阻隔性明显提高。结论经KH570硅烷偶联剂改性的二氧化硅对聚乳酸材料性能的增强效果更佳,为聚乳酸材料在包装领域的应用提供了依据。     

How hybridization with zinc oxide whiskers and carbon fibers affects the thermal diffusivity and mechanical properties of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) nanocomposites

The enhanced thermal diffusivity and mechanical properties of poly(l-lactic acid) (PLLA) nanocomposites reported here are based on the percolation network formed when PLLA is hybridized with short carbon fibers (CFs) and functionalized zinc oxide whiskers. The PLLA nanocomposite containing 30 wt% (≈9.5 vol%) ZnO whiskers and 10 wt% (≈8.1 vol%) CFs had a thermal diffusivity almost as high as that of stainless steel and an insulator-level electrical resistivity (>10¹⁰ Ωm). Modifying the surface of the ZnO whiskers by esterifying them using specific alcohols with long linear alkyl chains improved the elastic strength and toughness of the nanocomposites significantly. These results suggest that hybridizing PLLA with short CFs and functionalized ZnO whiskers yields nanocomposites with high thermal diffusivity as well as high electrical resistivity and excellent mechanical properties.     

Covalent grafting of carbon nanotubes to PLA in order to improve compatibility

An excellent methodology for the synthesis of nanocomposite materials using a biodegradable polymer as matrix (polylactic acid, PLA) and functionalized by Fenton reaction carbon nanotubes (fMWCNTs) as reinforcement was developed. PLA was modified with benzoyl chloride and both modified materials were bounded covalently by esterification reaction. Infrared spectroscopy (FTIR) and thermogravimetry (TGA) studies were performed to verify the synthesis of the composites obtained. Films based on modified PLA reinforced with fMWCNTs (PLAmfMWCNTs) were conformed observing excellent dispersion of the filler in the PLA matrix. Finally it was shown that the addition of fMWCNTs improves Young’s modulus and strength without losing deformation. Also it was observed that the good stability of the film let us to process it until 300 °C. Taking into account all these results, the new biodegradable nanocomposite material developed could be very promising to be used in packaging and biomedical industries as a replacement of the synthetic materials.     

Electrical, thermal, and mechanical properties of polyarylene ether nitriles/graphite nanosheets nanocomposites prepared by masterbatch route

Graphite nanosheets (GN) reinforced polyarylene ether nitriles (PEN) nanocomposites were successfully fabricated through masterbatch route and investigated for morphological, thermal electrical, mechanical, and rheological properties. The SEM images showed that GN were well coated by phthalonitrile prepolymer (PNP) and dispersed in the PEN matrix. Thermal degradation and heat distortion temperature of PEN/GN nanocomposites increased substantially with the increment of GN content up to 10 wt%. Electrical conductivity of the polymer was dramatically enhanced at low loading level of GN; the electrical percolation of was around 5 wt% of GN. The mechanical properties of the nanocomposites were also investigated and showed significant increase with GN loading. For 10 wt% of GN-reinforced PEN composite, the tensile strength increased by about 18%, the tensile modulus increased by about 30%, the flexural strength increased by about 25%, and the flexural modulus increased by 90%. Rheological properties of the PEN/GN nanocomposites also showed a sudden change with the GN loading content; the percolation threshold was in the range of 3–4 wt% of GN.