The effects of cellulose nanowhiskers on electrospun poly (lactic acid) nanofibres

The effects of cellulose nanowhiskers on the microstructure and thermal behaviour of electrospun poly (lactic acid) (PLA) nanofibres have been investigated in this study. The PLA/cellulose nanowhiskers composite nanofibres are successfully produced by electrospinning the mixtures of cellulose whiskers with PLA solution. The diameters of PLA and its composites are around 300 nm. The scanning electron micrographs show that the cellulose nanowhiskers do not protrude out of the outer surfaces of PLA nanofibres. The existence of cellulose nanowhiskers in the electrospun PLA matrix nanofibres, and the microstructural evolution are investigated by using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) analysis shows the formation trend of PLA α crystal with the addition of cellulose nanowhiskers. The electrospun PLA and PLA/cellulose nanowhiskers composites reveal very low crystallinity due to the rapid solvent evaporation and relatively slow crystallisation kinetics character of PLA. The electrospun nanofibres show particularly different thermal behaviour from that of the solution cast films. The nanofibres of pure PLA and PLA/cellulose nanowhiskers experience two consecutively overlapping crystallisation processes. The cellulose nanowhiskers act as heterogeneous sites for nucleation of PLA by decreasing the cold crystallisation onset temperature. The incorporation of cellulose nanowhiskers into PLA nanofibres is expected to improve mechanical properties and bring new functionalities to the electrospun matrix nanofibres.     

可生物降解聚乳酸/纳米纤维素复合材料的亲水性和降解性

采用溶液浇铸法制备可生物降解聚乳酸(PLA)/纳米纤维素复合材料。测试了该复合材料的吸水性,在37℃的磷酸缓冲溶液中及在土壤中的降解性。并用扫描电子显微镜(SEM)观察了降解前后复合材料的表面形貌。结果表明,随着复合材料中纳米纤维素质量分数的增加,复合材料的吸水性和降解性均随之提高,明显优于纯的聚乳酸。从SEM的图片中看出,降解后,在磷酸缓冲溶液中的复合材料表面有孔洞,而在土壤中的则有明显被侵蚀的痕迹。     

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.     

增容纳米纤维素/聚乳酸复合材料的制备与性能

采用接枝共聚法制备了马来酸酐和丙烯酸丁酯双单体接枝聚乳酸（PLA）共聚物（mPLA）,然后以mPLA为增容剂,通过溶液浇铸法制备纳米纤维素（NCC）/PLA复合材料。采用SEM、DSC、TG、广角X射线衍射（WXRD）、力学和降解性能测试研究了mPLA对NCC/PLA复合材料的结构和性能的影响。结果表明:mPLA在PLA与NCC之间起到了良好的界面增容作用,促进了NCC在PLA基体中的分散。更精细分散的NCC促进了PLA的结晶成核,复合材料的结晶温度降低,结晶度提高;NCC/mPLA/PLA复合材料的力学性能随着mPLA含量增加呈先上升后下降的趋势,当mPLA含量为8%时,复合材料的拉伸强度和弹性模量与未添加mPLA的复合材料相比,分别提高了30.2%和41.4%;亲水性的NCC加速了NCC/PLA复合材料的降解,加入mPLA后,复合材料的降解速率有所减慢,但仍然快于纯PLA的降解。      

聚乳酸/乙基纤维素复合膜的制备及其性能

以烯基琥珀酸酐( ASA) 作为新型增塑剂, 使用三氯甲烷作为聚乳酸( PLA) 和乙基纤维素( EC) 的共溶剂, 采用溶液浇铸法成功制备了聚乳酸/ 乙基纤维素复合膜。用红外光谱( FT IR) 、X 射线衍射(XRD) 表征了复合膜结构, 并测试了其吸水性和力学性能。FTIR 测试结果显示, 复合膜中存在强烈的氢键相互作用。XRD 表明,ASA 显著提高了PLA 和EC 2 种高聚物的界面黏合性。力学测试结果表明, ASA 对该复合膜具有良好的增塑效果。当膜中PLA 质量分数[ 37%时, PLA 对复合膜起增强作用。复合膜的吸水性随ASA 含量的增大而降低, 随PLA 含量的增大而提高。该复合膜作为一种潜在的药物缓释材料, 将具有广阔应用前景。      

In-depth study of mechanical properties of poly(lactic acid)/thermoplastic polyurethane/hydroxyapatite blend nanocomposites

Journal of Materials Science - The present study evaluates the effect of adding different contents of hydroxyapatite (HA) nanoparticles on the mechanical properties of poly(lactic...     

Enhanced ductility and tensile properties of hybrid montmorillonite/cellulose nanowhiskers reinforced polylactic acid nanocomposites

Montmorillonite (MMT)/cellulose nanowhiskers (CNW) reinforced polylactic acid (PLA) hybrid nanocomposites were prepared by solution casting. CNW were isolated from microcrystalline cellulose using a chemical swelling method. An initial study showed that the optimum MMT content, for mechanical properties, in a PLA/MMT nanocomposite is five parts per hundred parts of polymer (phr). Various amounts of CNW were added to the optimum formulation of PLA/MMT to produce PLA/MMT/CNW hybrid nanocomposites. FT-IR analysis indicated the formation of some polar interactions, resulting in enhanced tensile properties of the hybrid nanocomposites. The highest tensile strength for the hybrid nanocomposites was obtained for a 1 phr CNW content. Young’s modulus was also found to increase with an increasing CNW content. Interestingly, the strain to failure (or ductility) of the hybrid nanocomposites increased significantly from ~10 to ~90 % with the addition of 1 phr CNW. This increase in ductility was proposed to be due to the nucleation of crazes and the formation of shear bands in the PLA.     

Stress-transfer in microfibrillated cellulose reinforced poly(lactic acid) composites using Raman spectroscopy

Lyocell fibres were used to make microfibrillated cellulose (MFC) by combined homogenisation and sonication. A web-like structure was obtained with fibril diameters in the range of several micrometers to less than 80 nm. Composite samples with PLA resin reinforced with MFC networks were prepared using compression moulding. Young’s modulus and tensile strength of these composites increased by ～60% and 14% respectively, compared to the pure resin material. Raman spectroscopy was used to monitor the molecular deformation of networks and composite materials. A Raman band initially located at ～1095 cm^?1 was observed to shift towards a lower wavenumber position upon tensile deformation. The rate of Raman band shift with respect to strain for the composites was higher than for the pure MFC networks, indicating that the observed improvement in mechanical properties results from stress transfer from the PLA resin to the MFC fibrils.     

玉米秸秆微晶纤维素/聚乳酸复合膜的制备与性能

采用玉米秸秆微晶纤维素(CSCMC)作为增强材料, 生物可降解材料聚乳酸(PLA)作为基体, 制备了CSCMC/PLA复合膜材料, 并对复合膜的结晶度、热稳定性能、力学性能进行了测试。结果表明, 复合膜材料的热稳定性能和力学性能优于纯聚乳酸膜。当CSCMC的质量分数为10%时, 复合膜的热稳定性能和力学性能达到最佳, 与纯PLA膜相比, 起始分解温度提高了34.38 ℃, 拉伸强度提高了58.3%, 断裂伸长率提高了31.1%。      

Structure and thermal properties of poly(lactic acid)/cellulose whiskers nanocomposite materials

The goal of this work was to produce nanocomposites based on poly(lactic acid) (PLA) and cellulose nanowhiskers (CNW). The CNW were treated with either tert-butanol or a surfactant in order to find a system that would show flow birefringence in chloroform. The nanocomposites were prepared by incorporating 5 wt% of the different CNW into a PLA matrix using solution casting. Field emission scanning electron microscopy showed that untreated whiskers formed flakes, while tert-butanol treated whiskers formed loose networks during freeze drying. The surfactant treated whiskers showed flow birefringence in chloroform and transmission electron microscopy showed that these whiskers produced a well dispersed nanocomposite. Thermogravimetric analysis indicated that both whiskers and composite materials were thermally stable in the region between 25 °C and 220 °C. The dynamic mechanical thermal analysis showed that both the untreated and the tert-butanol treated whiskers were able to improve the storage modulus of PLA at higher temperatures and a 20 °C shift in the tan δ peak was recorded for the tert-butanol treated whiskers.     

Optical nanocomposites prepared by incorporating bacterial cellulose nanofibrils into poly(3-hydroxybutyrate)

A biocompatible polymeric nanocomposite was prepared by incorporating bacterial cellulose (BC) into a poly(3-hydroxybutyrate) (PHB) matrix. The transparency of the PHB/BC nanocomposite was high due to the homogeneous nano-sized spherulite and nanofibril of PHB and BC, which are smaller than the wavelength of visible rays. The X-ray diffraction patterns of the PHB in the nanocomposite film showed peaks corresponding to the crystallized PHB. The thermal stability of PHB in the nanocomposite film has been improved. The morphology studies showed that the PHB molecules filled vacancies between BC nanofibrils. An increase in the mechanical properties was observed by incorporating the BC into the PHB matrix. This PHB/BC nanocomposite can be considered for various applications, such as display devices, tissue engineering scaffold, and food packaging, because of its improved mechanical properties along with biodegradability and biocompatibility.     

Toughening mechanisms in poly(lactic) acid reinforced with TEMPO-oxidized cellulose

The mechanical properties of poly(lactic) acid (PLA) were modified by the addition of small amounts of cellulose, prepared from the mechanical disintegration of birch Kraft pulp following oxidation of the primary alcohol groups mediated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO). The TEMPO-fibrillated cellulose (TOFC) was subsequently acetylated in acetic anhydride to degrees of substitution (DS) of 0.4 and 0.6 to enhance the compatibility between the polar cellulose and the non-polar polymer. The fracture behaviour of tensile specimens prepared from PLA film containing weight fractions of 1, 2 and 5 % of TOFC was considerably altered. The strain-to-failure of PLA modified by the incorporation of 1 wt% TOFC acetylated to a DS of 0.6 increased approximately 25-fold and the work of fracture by order of magnitude. The increase in the fracture properties were, nevertheless, accompanied by a reduction in Young’s modulus of around 60 % at both DS levels. At the higher TOFC addition levels, no toughening was observed, with the strains-to-failure and works of fracture both decreasing compared to pure PLA film. On the other hand, the Young’s modulus and tensile strength of films prepared from PLA incorporating TOFC esterified to a DS of 0.6 was found to be greater than that of pure PLA film. Possible mechanisms explaining the increase in toughness at 1 wt% are postulated.     

Thermal and mechanical properties of biodegradable hydrophilic-hydrophobic hydrogels based on dextran and poly (lactic acid)

The thermal and mechanical properties of a new family of biodegradable hydrogels made of photocrosslinked dextran derivative of allyl isocyanate (dex-AI) and poly (D,L) lactide diacrylate macromer (PDLLAM) were studied. The changes of thermal and mechanical properties of the dex-AI/PDLLAM hydrogels as functions of dex-AI to PDLLAM composition ratio and immersion time in phosphate buffer solution at 37 °C were also investigated. Thermal property data showed that the chemical modification, crosslinking, swelling and hydrolytic degradation affected the glass transition and melting temperatures. Based on thermal data, no phase separation was observed in the bicomponent dex-AI/PDLLAM hydrogels. Mechanical property data showed that, by changing the composition ratio, dex-AI/PDLLAM hydrogels having a wide range of dry and swollen compression moduli could be obtained. The moduli of the dex-AI/DPLLAM hydrogels in dry state decreased with an increase in the PDLLAM composition due to the reduction in glass transition temperature of the hydrogels. The loss of mechanical strength in buffer solutions was attributed to the swelling-induced formation of 3D porous network structure in the early stage of immersion and the hydrolytic degradation of the PDLLAM in the late stage via the chain scission of ester linkages located in the PDLLAM backbone. Because swelling and degradation were composition dependent, the magnitude of the loss of mechanical strength was also composition-dependent.     

Processing of cellulose nanowhiskers/cellulose acetate butyrate nanocomposites using sol-gel process to facilitate dispersion

Biobased nanocomposites based on cellulose nanowhiskers (CNWs) and cellulose acetate butyrate (CAB) were prepared using solvent exchange of CNWs to ethanol by sol-gel method followed by casting. The strong flow birefringence of the solutions indicated evenly dispersed cellulose nanowhiskers in the dissolved polymer CAB. Scanning electron microscopy of the nanocomposites confirmed well dispersed CNWs in the CAB matrix, which was further supported by the high transparency exhibited by the nanocomposites. The results of tensile tests indicated significant improvements in the mechanical properties of nanocomposites by increasing the CNWs contents. The Young’s modulus and strength increased 83% and 70%, respectively, for nanocomposites with 12 wt% of CNW, and the strain was not suppressed compared to the neat CAB. The dynamic mechanical thermal analysis demonstrated significant improvement in storage modulus with increasing CNW contents, and the tan δ peak position was moved towards higher temperature when CNW was added. It is expected that solvent exchange by the sol-gel route followed by casting of nanocomposites from the same solvent will provide a promising route for obtaining cellulose nanocomposites with well dispersed CNW, leading to improved mechanical properties, even with low nanowhisker contents.     

Effect of extrusion drawing and twist-orientation on mechanical properties of self-reinforced poly(lactic acid) screws

In order to improve torsional strength of a bioabsorbable poly(lactic acid) (PLA) screw, twist-orientation method was developed in this study. PLA screws were prepared through a series of routes including compression molding, extrusion method, twist-orientation, and forging. Shear and torsional strength were measured as mechanical properties of screw. As a result, twist-orientation improves torsional strength of PLA screw without the decrease in shear strength. The maximum torsional strength was obtained at helix angle of 45° and extrusion ratio of 8. This is because fibrous crystals were oriented close to the direction of principal tensile stress which occurred during torsion test. Since this principal stress occurs in the 45° direction on the surface of specimen, the maximum torsional strength is achieved by twist-orientation at this helix angle.     

聚乳酸/蛭石纳米复合材料的原位聚合与性能研究

首次用原位聚合的方法制备了剥离型聚乳酸/蛭石纳米复合材料.以液态的单体丙交酯溶胀蛭石,然后引发单体进行聚合.XRD和TEM分析表明原位聚合法制备的纳米复合材料中蛭石片层完全剥离,分散与PLA基体中.用XRD和DSC分析和观察了聚乳酸/蛭石纳米复合材料基材的结晶性能,结果表明层状纳米蛭石聚乳酸的结晶度降低,球晶粒径大大降低.拉伸性能的考察表明制得的纳米复合材料的力学性能大大提高.     

Agrofibre reinforced poly(lactic acid) composites: Effect of moisture on degradation and mechanical properties

Natural fibre reinforced PLA composites are a 100% biobased material with a promising mechanical properties profile. However, natural fibres are hygroscopic whereas PLA is sensitive to hydrolytic degradation under melt processing conditions in the presence of small amounts of water. Here, we determine the effect of water content in undried and dried natural fibres on semi crystalline grade PLA degradation during processing as well as on the composite’s mechanical performance. The fibres evaluated are ramie, flax and cotton, containing 6–9 mass% moisture in the undried state and 0.2–0.4 mass% in the dried state. Intrinsic viscosity and melt flow index analysis indicate that the effect of the different levels of moisture in the fibres have a similar and small effect on PLA degradation, PLA hydrolysis appears rather affected by fibre diameter. Morphology, flexural strength and stiffness and Charpy impact of the composites are not significantly affected by the water present in the undried fibres.