聚乙二醇增容纳米纤维素/聚乳酸共混体系的研究

采用溶液浇铸法制备纳米纤维素/聚乳酸/聚乙二醇三元复合材料,与纯聚乳酸相比,该复合材料的抗张强度和断裂伸长率分别提高了41.2%和38.4%.傅立叶红外(FT-IR)表明聚乙二醇的存在使纳米纤维素和聚乳酸之间形成了强烈的氢键作用,明显改善了纳米纤维素和聚乳酸之间的相容性,提高了界面黏结力.扫描电子显微镜(SEM)观察了...     

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。      

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。      

Physico-chemical and mechanical properties of nanocomposites prepared using cellulose nanowhiskers and poly(lactic acid)

A range of nanocomposites were prepared using cellulose nanowhiskers (CNWs) and poly(lactic acid) (PLA) via a solvent casting process. Acid hydrolysis process was used to produce CNWs from bleached cotton. Structural morphology and surface topography of the CNWs and nanocomposites were examined using transmission (TEM) and scanning electron microscopy. TEM images revealed rod-like whiskers in the nano-scale region which were dispersed within the PLA matrix. The presence of the functional groups of CNWs and PLA were confirmed via FTIR analysis. Tensile tests were conducted on thin films and the nanocomposites containing 1 wt% CNWs showed a 34 and 31% increase in tensile strength and modulus, respectively, compared to pure PLA. The dynamic mechanical analysis showed that the tensile storage modulus also increased in the visco-elastic temperature region with increasing CNWs content in the nanocomposites. Thermogravimetric analysis showed that all the materials investigated were thermally stable from room temperature to 210 °C. A positive effect of CNWs on the crystal nucleation of PLA polymer in the nanocomposites was observed using differential scanning calorimetry and X-ray diffraction analysis. The degradation profiles of the nanocomposites in deionised water over 1 week revealed a mass loss of 1.5–5.6% at alternate temperatures (25, 37 and 50 °C) and at the same conditions the swelling ratio and water uptake were seen to increase with CNWs content in the nanocomposites, which was strongly influenced by the presence of crystalline CNWs.     

Effect of fiber surface-treatments on the properties of poly(lactic acid)/ramie composites

Ramie fiber reinforced poly(lactic acid) (PLA) composites were prepared by a two-roll mill. Ramie was treated by alkali and silane (3-aminopropyltriethoxy silane and γ-glycidoxypropyltrimethoxy silane). Effect of surface treatment on the properties of the composites was studied. The tensile, flexural and impact strength of the composites have a significant improvement. Dynamic mechanical analysis (DMA) results show that the storage moduli of the composites with treated ramie increase with respect to the plain PLA and the composites with untreated fiber whereas tangent delta decreases. The Vicat softening temperature of the composites with treated fiber is greatly higher than that of the composites with untreated fiber. The results of thermogravimetric analysis (TGA) show that fiber treatment can improve the degradation temperature of the composites. Moreover, the morphology of fracture surface evaluated by scanning electron microscopy (SEM) indicates that surface treatment can get better adhesion between the fiber and the matrix.     

聚乳酸/小麦秸秆纤维复合材料降解性能研究

以聚乳酸为基体,以小麦秸秆纤维为增强体制备聚乳酸/小麦秸秆纤维复合材料。通过测试该复合材料在不同pH值PBS缓冲液降解过程中的吸水率、质量损失率和拉伸性能,并用扫描电子显微镜(SEM)观察降解过程中复合材料的表面形貌变化,研究其随时间变化的降解性能。结果表明,在不同pH值的PBS缓冲液中,聚乳酸/小麦秸秆纤维复合材料的吸水率、质量损失率都随着降解时间的增加而增大,但后期增大比较缓慢;复合材料在弱碱性环境中降解最快,弱酸性环境次之,中性环境最慢;随着降解时间的增加,复合材料的拉伸强度和杨氏模量明显降低,表面由光滑变成凹凸不平,小麦秸秆纤维裸露在表面。     

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%。      

凹凸棒黏土对聚乳酸结晶性能和热稳定性能的影响

采用熔融共混法分别制备了凹凸棒黏土质量分数为1％、3％和5％的纳米凹凸棒黏土(ATT)/聚乳酸(PLA)复合材料,研究了ATT对PLA结晶性能和热稳定性能的影响.结果表明,ATT与PLA基体具有较好的相容性,当ATT含量低于3％时,可以均匀的分散在PLA基体中,而达到5％时则会发生团聚.FTIR结果表明,ATT与PLA基体之间存在较强的相互作用.ATT可明显促进PLA的结晶,起到异相成核的作用.ATT纳米颗粒的添加引起了PLA冷结晶峰向低温方向移动,使冷结晶温度从114.4℃降低至103℃左右.含ATT体系结晶速率比纯PLA快,表明ATT的加入可以促进PLA的结晶,说明ATT是PLA有效的成核剂之一.添加ATT可明显加快PLA的结晶速率并减小球晶尺寸.当添加3％ATT时,ATT/PLA复合材料的热分解温度比纯PLA提高了11℃,这主要是由于ATT/PLA网络密度的提高,使ATT在PLA的降解过程中能够起到较好的阻隔作用,抑制了PLA的降解自加速过程.     

凹凸棒黏土对聚乳酸结晶性能和热稳定性能的影响

采用熔融共混法分别制备了凹凸棒黏土质量分数为1%、 3%和5%的纳米凹凸棒黏土(ATT)/聚乳酸(PLA)复合材料, 研究了ATT对PLA结晶性能和热稳定性能的影响。结果表明, ATT与PLA基体具有较好的相容性, 当ATT含量低于3%时, 可以均匀的分散在PLA基体中, 而达到5%时则会发生团聚。FTIR结果表明, ATT与PLA基体之间存在较强的相互作用。ATT可明显促进PLA的结晶, 起到异相成核的作用。ATT纳米颗粒的添加引起了PLA冷结晶峰向低温方向移动, 使冷结晶温度从114.4 ℃降低至103 ℃左右。含ATT体系结晶速率比纯PLA快, 表明ATT的加入可以促进PLA的结晶, 说明ATT是PLA有效的成核剂之一。添加ATT可明显加快PLA的结晶速率并减小球晶尺寸。当添加3%ATT时, ATT/PLA复合材料的热分解温度比纯PLA提高了11 ℃, 这主要是由于ATT/PLA网络密度的提高, 使ATT在PLA的降解过程中能够起到较好的阻隔作用, 抑制了PLA的降解自加速过程。     

Effect of recycling on rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend

A continued increase in the use of plastics has led to an increasing amount of plastics ending up in the waste stream; and the increasing cost of landfill disposal and public interest in support of recycling has meant that plastics recycling must increase. In this work, the effect of multiple extrusion and injection of poly(lactic acid)/polystyrene polymer blend (PLA/PS) on its rheological and mechanical properties is presented. Rheological properties were studied using a capillary rheometer, apparent shear rate (γ _a), apparent shear stress (τ _a), apparent viscosity (η _a), and flow activation energy were determined. The mechanical properties of the blend were investigated on dog bone-shaped samples obtained by injection molding, tensile tests were performed, stress at break, strain at break, and Young’s modulus were determined. The results showed that the apparent viscosity of PLA/PS blend decreases monotonously with increasing the processing number. Also it was found that stress and strain at break of the blend decrease sharply after two processing cycles, whereas the processing number has a little effect on Young’s modulus.     

Structural characterization and thermal and mechanical properties of poly(propylene carbonate)/MgAl-LDH exfoliation nanocomposite via solution intercalation

Poly(propylene carbonate)/MgAl layered double hydroxide (PPC/MgAl-LDH) exfoliated nanocomposites were synthesized by solution intercalation of PPC into the galleries of organic modified MgAl-LDH (OMgAl-LDH) in cyclohexanone. The crystal morphological structures, thermal degradation behavior, and mechanical properties have been studied by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, and thermogravimetric analysis (TGA). The nanoscale dispersion of OMgAl-LDH layers in the PPC matrix has been verified by the disappearance of d_0 0 1 XRD diffraction peak of OMgAl-LDH and the observation of TEM image. The TGA data give evince that the thermal degradation temperature of the exfoliated PPC/MgAl-LDH nanocomposites with 1% OMgAl-LDH is 10 °C higher than that of pure PPC resin when 20% weight loss was selected as a point of comparison. The data from the mechanical test show that the tensile strength of the PPC/MgAl-LDH nanocomposites with 5% LDH is 36.9 MPa, which is 72% and 30% higher than those of pure PPC resin and simple mixed sample with the same content of LDH, and its Young’s modulus is 1303 MPa, which is 57% and 21% higher than those of the same two samples, respectively.     

Thermal and optical properties of poly(methyl methacrylate)/calcium carbonate nanocomposite

The study deals with thermal and optical properties of poly(methyl methacrylate) (PMMA) containing 2wt% calcium carbonate (CaCO₃) nanofiller. It was found that the thermal conductivity increases with increasing temperatures, due to thermal activation of the phonons in the PMMA/CaCO₃ nanocomposite. This enhancement in the thermal conduction is mainly attributed to the heat transferred by lattice vibrations as major contributors and electrons as minor contributors during thermal conduction. The optical properties were investigated as a function of wavelength and photon energy of UV radiation. The optical results obtained were analysed in terms of absorption formula for noncrystalline materials. It was found that the measured optical energy gap for the pure PMMA is greater than the PMMA/CaCO₃ nanocomposite. The width of the energy tails of the localised states was calculated. Adding CaCO₃ nanofiller into PMMA matrix may cause the localised states of different colour centres to overlap and extend in the mobility gap. This overlap may give an evidence for decreasing energy gap when adding CaCO₃ nanofiller in the polymer matrix.     

Effect of multi-walled carbon nanotube dispersion on the electrical and rheological properties of poly(propylene carbonate)/poly(lactic acid)/multi-walled carbon nanotube composites

In this study, the morphological, electrical, and rheological properties of the poly(propylene carbonate) (PPC)/poly(lactic acid) (PLA)/multi-walled carbon nanotube (MWCNT) composites were investigated. From the results of transmission electron microscopy of the PPC/PLA/MWCNT composites, the MWCNT preferred to locate more in the PPC phase than in the PLA phase. This maybe due to the lower interfacial tension of the PPC/MWCNT composites compared to that of the PLA/MWCNT composites. The electrical conductivities of the PPC/PLA/MWCNT composites were higher than those of the PPC/MWCNT and the PLA/MWCNT composites, which was likely due to the selective localization of the MWCNT in the PPC phase (continuous phase). From the results of the complex viscosity of the composites, the ratio of increasing the complex viscosity of the PPC/MWCNT composites with the MWCNT content was higher than that of the PLA/MWCNT composites. This is maybe due to the fact that the MWCNT dispersion in the PPC phase was higher than in the PLA phase. The results from the morphology, electrical conductivity, and complex viscosity of the PPC/PLA/MWCNT composites suggest that the selective localization of the MWCNT in the PPC phase can improve the conductive path and increase the electrical conductivity of the PPC/PLA/MWCNT composites.     

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...     

Scaffolds for drug delivery,part I: electrospun porous poly(lactic acid) and poly(lactic acid)/poly(ethylene oxide) hybrid scaffolds

This is the first in a series of papers, focused on the development of a biodegradable, controlled, and potentially targeted drug delivery system. In this paper, we describe the production of highly porous biodegradable fibrous structures suitable for biomedical applications and as a matrix for drug delivery. Two structures are described below. The first structure is composed of electrospun poly(lactic acid) (PLA) fibers and is unique due to (1) the uniformity if its constitute fibers’ diameter, (2) consistent surface pore dimensions of each fiber, (3) the use of only a single solvent, (4) interior nano-size porosity throughout each individual fiber, and (5) the independency of surface pore dimensions on fiber diameter. The produced matrix will be further impregnated with cargo loaded nanoparticles—Red clover necrotic mosaic virus (RCNMV)—to achieve a controlled drug delivery system (described in Part III) for cancer treatments. Such a structure can also be used as tissue engineering scaffolds and filter media. The second electrospun structure has enhanced hydrophilicity compared to PLA matrix and is formed by blending poly(lactic acid)/poly(ethylene oxide) (PEO) polymers. The incorporation of PEO in the matrix introduces preferable sites for aqueous compounds to be attached to while retaining the overall structural integrity and porous morphology. It is hypothesized that the existence of alternative hydrophilic and hydrophobic segments in the structure may reduce post-implantation complications such as platelet adhesion.     

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.     

Preparation and properties of biodegradable poly(lactic acid)/poly(butylene adipate-co-terephthalate) blend with glycidyl methacrylate as reactive processing agent

Poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) were melt-blended in the presence of glycidyl methacrylate (GMA) by twin-screw extrusion. The physical properties, phase morphology, thermal properties, and melt rheological behavior of the blends were investigated by tensile tests, Charpy impact tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and advanced rheology expended system (ARES). With 2 or 5 wt% GMA, the tensile toughness of the PLA/PBAT blend was greatly increased without severe loss in tensile strength. The impact strength of the blend was also significantly improved at 1 wt% of GMA addition but ultimately trended to be saturated with increasing GMA. SEM micrographs revealed that better miscibility and more shear yielding mechanism were involved in the toughening of the blend. DSC results indicated that the blend is still a two-phase system in the presence of reaction agent and the addition of GMA was found to enhance the interfacial adhesion between PLA and PBAT. Rheological results revealed that the addition of T-GMA increased the storage moduli (G′), loss moduli (G′′) and complex viscosity of the blends at nearly all frequencies. The decreased shear-thinning tendency of the blends in the presence of T-GMA also implied improved melt stability during processing.     

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.