Mechanical and thermal properties of wood fibers reinforced poly(lactic acid)/thermoplasticized starch composites

Thermoplasticized starch (TPS) filled poly(lactic acid) (PLA) blends are usually found to have low mechanical properties due to poor properties of TPS and inadequate adhesion between the TPS and PLA. The purpose of this study was to investigate the reinforcing effect of wood fibers (WF) on the mechanical properties of TPS/PLA blends. In order to improve the compatibility of wood with TPS/PLA blends, maleic anhydride grafted PLA (MA‐g‐PLA) copolymer was synthesized and used. TPS, TPS/PLA blends, and WF reinforced TPS/PLA composites were prepared by twin‐screw extrusion and injection molded. Scanning electron microscope and crystallinity studies indicated thermoplasticity in starch. WF at two different weight proportions, that is, 20% and 40% with respect to TPS content were taken and MA‐g‐PLA at 10% to the total weight was chosen to study the effect on mechanical properties. At 20% WF and 10% MA‐g‐PLA, the tensile strength exhibited 86% improvement and flexural strength exhibited about 106% improvement over TPS/PLA blends. Increasing WF content to 40% further enhanced tensile strength by 128% and flexural strength by 180% with respect to TPS/PLA blends. Thermal behavior of blends and composites was analyzed using dynamic mechanical analysis and thermogravimetric analysis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46118.     

聚乳酸基木塑复合材料的相容性研究

以聚乳酸(PLA)、松木粉为主要原料,用双螺杆挤出机制备了PLA基木塑复合材料。研究了硅烷偶联剂和增容剂对PLA基木塑复合材料力学性能和结构形态的影响。结果表明,硅烷偶联剂可以增加PLA与木粉之间的界面结合力,但是对体系的力学性能影响不是很大;增容剂的加入能够提高复合材料的力学性能。     

Enhancing the durability of poly(lactic acid) composites by nucleated modification

Biodegradable poly(lactic acid) (PLA) composites were prepared using an innovative combination of wood fiber (WF) and 1,3,2,4‐bis(3,4‐dimethylobenzylideno)sorbitol (DMDBS). DMDBS acted as an effective nucleating agent, which improved the mechanical properties and slowed down the degradation of the WF/PLA composites. The enzymatic degradation of the composites was examined by immersing in proteinase K or cellulase buffer. The presence of DMDBS resulted in a 26.7% increase of the crystallinity compared to the WF/PLA composites. The increase in crystallinity enhanced the thermal stability and tensile strength of the WF/DMDBS/PLA composites by 8.5%. The durability of the WF/DMDBS/PLA composites after nucleated modification was enhanced after enzymolysis. After nucleated modification, the surface of the WF/PLA composites showed clear cracks due to degradation, while these appeared about 2 weeks later in the case of the WF/DMDBS/PLA composites. The results revealed that the introduction of cellulase degraded WF in the composites, which increased hydrolysis or enzymolysis sites. The combination of nucleated modification and enzyme buffer gave an expanded downstream application of WF/PLA composites in packaging and agricultural materials. © 2019 Society of Chemical Industry     

Bleached extruder chemi‐mechanical pulp fiber‐PLA composites: Comparison of mechanical,thermal, and rheological properties with those of wood flour‐PLA bio‐composites

An environmentally friendly bleached extruder chemi‐mechanical pulp fiber or wood flour was melt compounded with poly(lactic acid) (PLA) into a biocomposite and hot compression molded. The mechanical, thermal, and rheological properties were determined. The chemical composition, scanning electron microscopy, and Fourier transform infrared spectroscopy results showed that the hemicellulose in the pulp fiber raw material was almost completely removed after the pulp treatment. The mechanical tests indicated that the pulp fiber increased the tensile and flexural moduli and decreased the tensile, flexural, and impact strengths of the biocomposites. However, pulp fiber strongly reinforced the PLA matrix because the mechanical properties of pulp fiber‐PLA composites (especially the tensile and flexural strengths) were better than those of wood flour‐PLA composites. Differential scanning calorimetry analysis confirmed that both pulp fiber and wood flour accelerated the cold crystallization rate and increased the degree of crystallinity of PLA, and that this effect was greater with 40% pulp fiber. The addition of pulp fiber and wood flour modified the rheological behavior because the composite viscosity increased in the presence of fibers and decreased as the test frequency increased. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44241.     

Effects of alkali treatment on the properties of WF/PLA composites

In this study, composites of thermoplastic poly (lactic acid) filled with wood flour (WF) were prepared via melt extrusion. Before that, alkali treatment was performed on WF to improve the properties of the WF/PLA composite materials. The effect of the solution concentrations of NaOH, namely 0.5, 1.0, 5.0, and 10.0%, on mechanical properties of the composites was evaluated. The results showed that the properties of the composites with treated WF were enhanced greatly compared with that of the untreated composites. The composites had a best improvement in its compatibility and mechanical strength when the concentration of NaOH solution was 5.0%. The brittle fracture of composites showed that the chemical modification of WFs improved the compatibility between the filler and matrix.     

Effects of the chain‐extender content on the structure and performance of poly(lactic acid)–poly(butylene succinate)–microcrystalline cellulose composites

Composites of poly(lactic acid) (PLA) with poly(butylene succinate) (PBS) and microcrystalline cellulose (MCC) as reinforcements of the polymer matrix were prepared by melt blending to improve the brittleness of PLA. As a reactive compatibilizer, a chain extender was used in an attempt to solve the composites’ interfacial problems and to improve their mechanical properties; Fourier transform infrared spectroscopy indicated that the chain extender functionally reacted with PLA, PBS, and MCC mainly through end carboxyls or end hydroxyls. Scanning electron microscopy indicated that the chain extender significantly improved the cohesive interfacial forces. Differential scanning calorimetry and X‐ray diffraction showed that the chain extender inhibited crystallization, and these effects were greater when its percentage was increased. The addition of chain extender improved the tensile and impact strength of the composites, and this improvement was proportional to the chain‐extender percentage. However, the elongation at break decreased when the chain‐extender percentage was over 0.5% because of mild crosslinking within the resin matrix. Rheology indicated that the complex viscosity and storage and loss moduli of the composites increased with increasing amount of chain extender; this indicated that the addition of chain extender improved the melt strength and processability of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44895.     

马来酸酐/二乙烯基苯接枝聚乳酸对微晶纤维素/聚乳酸复合材料性能的影响

研究了马来酸酐(MAH)/二乙烯基苯(DVB)接枝聚乳酸(PLA-g-DVB/MAH)对微晶纤维素(MCC)/聚乳酸(PLA)复合材料性能的影响。首先采用熔融接枝法,将DVB作为MAH的共聚单体接枝到PLA分子链上制备PLA-g-DVB/MAH接枝聚合物,然后以PLA-g-DVB/MAH为相容剂,采用注射成型法制备MCC/PLA复合材料。利用FTIR对PLA-g-DVB/MAH进行表征,探究了PLA-g-DVB/MAH对MCC/PLA复合材料流变及力学性能的影响。结果表明,MAH成功接枝到PLA上,并得到接枝聚合物PLA-g-DVB/MAH;添加PLA-g-DVB/MAH后,MCC/PLA复合材料的储能模量、复数黏度、平衡扭矩以及剪切热都有明显升高;PLA-g-DVB/MAH的添加有利于改善MCC和PLA的界面相容性,进而提高了MCC/PLA复合材料的力学性能。     

Evaluation of microcrystalline cellulose prepared from kenaf fibers

A series of microcrystalline cellulose (MCC) were prepared from bleached kraft pulp of kenaf bast and core and compared with that from wood pulp. Hydrolysis of three kinds of pulp was carried out using hydrochloric acid. The properties of the produced MCC such as degree of polymerization (DP), crystallinity index (CrI), morphological features, bulk and tapping density, particle size and particle size distribution were examined, respectively. Highly native crystalline cellulose I form was characterized from all MCC samples. CrI values indicated that MCC from kenaf core (MCC-C) was more amorphous than both MCC from kenaf bast (MCC-B) and MCC from wood pulp (MCC-W). SEM micrographs showed that MCC-B and MCC-W displayed a rod-shaped morphology in their aggregates; MCC-C appeared to be a form of clusters. MCC-B had higher bulk and tapping density followed by MCC-W and MCC-C. The particle size distribution patterns indicated that all kinds of MCC samples fitted log-normal distribution and particle size mostly located in the range of 2–500 μm.     

Preparation of acylated microcrystalline cellulose using olive oil and its reinforcing effect on poly(lactic acid) films for packaging application

A novel poly(lactic acid) (PLA) based composite, reinforced by microcrystalline cellulose (MCC) was prepared. MCC was modified by esterification reaction using olive oil for improving the compatibility with PLA matrix. The acylated microcrystalline cellulose (AMCC) exhibited reduced polarity in comparison to unmodified MCC. AMCC/ PLA composite films were prepared using solvent casting technique. The effects of the MCC surface modification on morphological, mechanical, physical, thermal, biodegradability and barrier properties of the PLA based MCC composites were studied. FTIR analysis confirmed acylation reaction of MCC. Scanning electron microscopy analysis exhibited a uniform distribution of AMCC in PLA matrix. Barrier properties of AMCC based composites were improved as compared to MCC based composites. The tensile strength and tensile modulus of composite films (at 2 wt.% AMCC) were improved about 13% and 35% as much as those of the pure PLA films, respectively. These biodegradable composite films can be a sustainable utilization of olive oil and microcrystalline cellulose in the food packaging application.     

Physical,mechanical, and thermal properties of micronized organo‐montmorillonite suspension modified wood flour/poly(lactic acid) composites

In this study, micronized organo‐montmorillonite (OMMT) suspension was prepared with sodium‐montmorillonite (Na‐MMT), didecyl dimethyl ammonium chloride, and dispersant polyethylene glycol 1000 by a ball‐milling process. Then, wood flours (WFs) were impregnated with prepared OMMT suspension at a concentration of 0.5, 1.0, 2.0, or 4.0%. WFs were characterized by X‐ray diffraction and scanning electron microscopy. The hygroscopicity of WF was investigated by a vapor adsorption method. WFs were, respectively, blended with poly (lactic acid) (PLA) to produce WF/PLA composites. Thereafter, physical, mechanical, and thermal properties of the composites were tested. The results showed that a great amount of OMMT attached on the surface of WF, partly penetrating into the microstructure of WF. Owing to the hydrophobicity of OMMT, the vapor adsorption of OMMT‐modified WF decreased. The composite which was produced by WF treated with 0.5% OMMT suspension, showing an increment in the physical, mechanical, and thermal properties. However, OMMT should not be overloaded. Otherwise, the accumulation of OMMT might cause poor interfacial adhesion between WF and PLA matrix. POLYM. COMPOS., 36:731–738, 2015. © 2014 Society of Plastics Engineers     

Properties of grafted wood flour filled poly (lactic acid) composites by reactive extrusion

Composites of poly(lactic acid) with wood flour which was grafted by melt extruding with methyl acrylate in the presence of benzoyl peroxide (BPO) were investigated. The modification of filler (WF-g-PMA) was carried out to enhance the filler-matrix interactions, while the treated component was characterized by infrared spectrum. Properties of binary (PLA/WF, PLA/WF-g-MA) composites were analyzed as a function of the grafting monomer amount by scanning electron microscopy, differential scanning calorimeter, thermogravimetric analysis, water absorption and mechanical tests. Compared with the untreated system (PLA/WF), all treated composites showed higher interfacial compatibility as a result of chemical bonding between WF and grated monomer. All composites showed higher tensile modulus and lower strength and elongation at break as compared to pure PLA; grafting modification with methyl acrylate led to an increased stiffness and decreased water absorption of the composites because of an enhanced filler-matrix interfacial compatibility.     

Mechanical properties of acrylonitrile–butadiene–styrene copolymer/poly(l‐lactic acid) blends and their composites

As the material properties of acrylonitrile–butadiene–styrene copolymer (ABS) have an excessively wide margin for applications in automobile console boxes, ABS partly replaced with poly(l ‐lactic acid) (PLA) may be used for the same purpose with improved ecofriendliness if the corresponding deterioration of the material properties is acceptable through the choice of appropriate additives. ABS composites with 30 wt % renewable components (PLA and cellulose pulp) were prepared by melt compounding, and the material properties were examined as a function of the additive content. The changes in the mechanical properties of the ABS/PLA blends were examined after the addition of cellulose pulp and two clays [Cloisite 25A (C25A) and sodium montmorillonite] as well as these two clays treated with bis(3‐triethoxysilylpropyl)tetrasulfide (TESPT). The heat distortion temperatures of the composites were measured as a function of the content of the TESPT‐treated C25A. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40329.     

Facile Preparation of Cellulose/Polylactide Composite Materials with Tunable Mechanical Properties

A solvent-free route was developed to fabricate 100% biobased, renewable, and degradable polylactide (PLA) composites reinforced with ball-milled celluloses. The results show that the original pulp cellulose fibers were modified to partial amorphization through 30-min ball milling. Filling the ball milled celluloses into PLA increased the tensile modulus for the resultant cellulose/PLA composite materials, while decreased their tensile strength and impact resistance. This method can be used to access the cost-efficient PLA-based composite materials with tunable mechanical properties. The variation analysis shows that filling content contributed more to the variations of their mechanical properties than that particle size did.     

Mechanical and thermal properties,morphology and relaxation characteristics of poly(lactic acid) and soy flour/wood flour blends

Poly(lactic acid) (PLA) is a biodegradable polymer derived from sugar‐based materials, and its applications are varied. PLA blends are commonly employed to overcome certain disadvantages such as poor impact strength, low heat distortion temperature, poor processability and relatively high cost. In this study, blending PLA with soy flour (SF), wood flour (WF) and sodium bisulfite‐modified SF was used to improve the adhesion to PLA. In all cases, 0.5 wt% methylenediphenyl diisocyanate (MDI) was used as a coupling agent. Mechanical and thermal properties, morphology and relaxation characteristics of the blends were investigated. The results showed that MDI was an effective coupling agent for the WF/PLA system in improving tensile strength and elongation. Differential scanning calorimetry results indicated that SF and modified SF act as nucleation agents and facilitate the crystallization behavior of PLA by increasing the percentage crystallinity. From mechanical relaxation of the temperature‐variant system, we determined how the mechanical relaxation time evolves during the course of heating and obtained the Kohlrausch–Williams–Watts parameter and activation energy (ΔE). PLA and its blends exhibited highly homogeneous relaxational dynamics in their transition from glass to liquid, and ΔE of PLA and its blends is mainly affected by their densities and compositions. Copyright © 2010 Society of Chemical Industry     

Surface modification of spruce wood flour and effects on the dynamic fragility of PLA/wood composites

Poly (lactic acid) (PLA), a biodegradable aliphatic semicrystalline polyester was filled with 40 wt% spruce wood flour (WF), to produce composite materials. Hydrothermal treatment, as well as maleic anhydride, vinyltrimethoxysilane, and stearic acid surface treatments were applied. The influence of surface modifications for WF was tested in terms of thermal, mechanical, and viscoelastic properties. The recorded results show that in both, the untreated and treated PLA/WF composites, the rigid amorphous phase content has been enhanced. The presence of WF causes a stiffness increase of the PLA/WF composites, while damping factor was decreased. The effect of wood surface modifications on interfacial compatibility with PLA was estimated by dynamic fragility parameter m calculated according the Williams‐Landel‐Ferry equation. The incorporation of untreated WF increased dynamic fragility of PLA/WF composites markedly, whereas used silane, maleic anhydride and hydrothermal treatments lead to lower values of parameter m. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Design of new polypropylene–woodflour composites: Processing and physical characterization

Woodflour/polypropylene composites were prepared with 10 and 20% in weight of woodflour (WF). The influence of the WF, the compatibilizer, and processing aid (WP) in the crystalline structure of the polypropylene was studied by thermal analysis. The results showed that the WF acts as a nucleating agent, increasing the crystallization rate of the PP at the cooling rates studied. The morphological study by SEM proved that the WP increased the dispersion of the filler into the PP matrix, and the ionomer, used like compatibilized improved the adhesion between the PP and the filler obtaining a more uniform morphology. The mechanical properties indicated that the incorporation of the ionomer and the WP enhanced the ductility of the composites at the same time that the materials reached a more uniform morphology. The amount of additives (compatibilizer and WP) included in the woodflour-plastic composite (WPC) formulations was small, for this, the formulations are suitable to use in a possible industrial application. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The effects on mechanical properties and crystallization of poly (l‐lactic acid) reinforced by cellulosic fibers with different scales

Bacterial cellulose (BC), microcrystalline cellulose (MCC), and bamboo cellulosic fibers (BCFs) were used to reinforce poly(l ‐lactic acid) (PLLA) based bio‐composites. The mechanical properties and crystallization of the composites were studied through mechanical testing, differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, and polarizing microscope. The incorporation of all three kinds of cellulose increased the stiffness of the composites compared to pure PLLA. The reinforcing effect of the MCC in the composites is most significant. The Young's modulus and impact toughness of the MCC/PLLA composites were increased by 44.4% and 58.8%, respectively. The tensile strength of the MCC/PLLA composites was increased to 71 MPa from 61 MPa of PLLA. However, the tensile strength of the composites reinforced with BCF or BC was lower than PLLA. The three kinds of cellulosic fibers improved the crystallization of PLLA. The BC with smallest size provided the composites with smallest grain and highest crystallinity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41077.     

Poly(vinyl alcohol)–lignin blended resin for cellulose‐based composites

Wood has limitations in strength because of its biostructural defects, including vessels. To overcome this limitation, composite materials can be innovated by breaking wood down into cellulose and lignin and reassembling them for bio‐originating strong structural materials. In this study, an ecofriendly resin was developed that was suitable for cellulose‐based composites. To overcome the low dimensional stability of lignin and to increase its interactions with cellulose, it was blended with poly(vinyl alcohol) (PVA). The PVA–lignin resin was characterized with scanning electron microscopy, Fourier transform infrared spectroscopy, thermal analysis, mechanical tensile testing, and lap‐shear joint testing. The adhesion properties of the PVA–lignin resin increased with increasing PVA content. PVA played the role of synthetic polymer and that of linker between the cellulose and lignin, like hemicellulose does in wood. The PVA–lignin resin exhibited a high miscibility, mechanical toughness, and good adhesion properties for nanocellulose composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46655.     

Poly(lactic acid)-based biocomposites reinforced with kenaf fibers

Biodegradable thermoplastic-based composites reinforced with kenaf fibers were prepared and characterized. Poly(lactic acid) (PLA) was selected as polymeric matrix. To improve PLA/fibers adhesion, low amount of a proper reactive coupling agent, obtained by grafting maleic anhydride onto PLA, was added during matrix/fibers melt mixing. Compared with uncompatibilized composites, this compatibilization strategy induces a strong interfacial adhesion and a pronounced improvement of the mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of poly(vinyl alcohol) nanocomposites made from cellulose nanofibers

A method using a combination of ball milling, acid hydrolysis, and ultrasound was developed to obtain a high yield of cellulose nanofibers from flax fibers and microcrystalline cellulose (MCC). Poly(vinyl alcohol) (PVA) nanocomposites were prepared with these additives by a solution‐casting technique. The cellulose nanofibers and nanocomposite films that were produced were characterized with Fourier transform infrared spectrometry, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Nanofibers derived from MCC were on average approximately 8 nm in diameter and 111 nm in length. The diameter of the cellulose nanofibers produced from flax fibers was approximately 9 nm, and the length was 141 nm. A significant enhancement of the thermal and mechanical properties was achieved with a small addition of cellulose nanofibers to the polymer matrix. Interestingly, the flax nanofibers had the same reinforcing effects as MCC nanofibers in the matrix. Dynamic mechanical analysis results indicated that the use of cellulose nanofibers (acid hydrolysis) induced a mechanical percolation phenomenon leading to outstanding and unusual mechanical properties through the formation of a rigid filler network in the PVA matrix. X‐ray diffraction showed that there was no significant change in the crystallinity of the PVA matrix with the incorporation of cellulose nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009