The morphology,rheological, and mechanical properties of wood flour/starch/poly(lactic acid) blends

An entirely biosourced blend composed of poly(lactic acid) (PLA), starch, and wood flour (WF) was prepared by a co‐extruder with glycerol as a plasticizer. The morphology, rheological properties, and mechanical properties of the WF/starch/PLA blends were comprehensively analyzed. The results showed that with the decrease of the starch/WF ratio, the morphology experienced a large transformation, and the compatibility of the blends was found to be superior to other blends, with a starch/wood flour ratio of 7/3. The dynamic mechanical thermal analysis (DMA) results demonstrated the incompatibility of the components in WF/starch/PLA blends. Following the decrease of the starch/WF ratio, the storage modulus (G″) and the complex viscosity (η*) of the blends increased. The mechanical strength first increased, and then decreased with the increase of the WF concentration. The water absorption results showed that the water resistance of the blends was reduced with the lower starch/WF ratio. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44743.     

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 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     

Thermal and dynamic mechanical behavior of poly(vinyl chloride)/wood flour composites

Thermal and dynamic mechanical behaviors of wood plastic composites made of poly vinyl chloride (PVC) and surface treated, untreated wood flour were characterized by using differential scanning calorimetry and dynamic mechanical analysis. Glass transition temperature (T_g) of PVC was slightly increased by the addition of wood flour and by wood flour surface treatments. Heat capacity differences (ΔC_p) of composites before and after glass transition were markedly reduced. PVC/wood composites exhibited smaller tan δ peaks than PVC alone, suggesting that less energy was dissipated for coordinated movements and disentanglements of PVC polymer chains in the composites. The rubbery plateaus of storage modulus (E′) curves almost disappeared for PVC/wood composites in contrast to a well defined plateau range for pure PVC. It is proposed that wood flour particles act as “physical crosslinking points” or “pinning centers” inside the PVC matrix, resulting in the absence of the rubbery plateau and high E′ above T_g. The mobility of PVC chain segments were further retarded by the presence of surface modified wood flour. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of miscibility on mechanical and thermal properties of poly(lactic acid)/ polycaprolactone blends

Binary blends based on poly(lactic acid) (PLA) and polycaprolactone (PCL) were prepared by melt mixing in a twin‐screw co‐rotating extruder in order to increase the low intrinsic elongation at break of PLA for packaging applications. Although PLA and PCL show low miscibility, the presence of PCL leads to a marked improvement in the ductile properties of PLA. Various mechanical properties were evaluated in terms of PCL content up to 30 wt% PCL. In addition to tensile and flexural properties, Poisson's ratio was obtained using biaxial extensometry to evaluate transversal deformations when axial loads are applied. Very slight changes in the melt temperature and glass transition temperature of PLA are observed thus indicating the low miscibility of the PLA–PCL system. Field emission scanning electron microscopy reveals some interactions between the two components of the blend since the morphology is characterized by non‐spherical polycaprolactone drops dispersed into the PLA matrix. In addition to the improvement of mechanical ductile properties, PCL provides higher degradation rates of blends under conditions of composting for contents below 22.5% PCL. © 2016 Society of Chemical Industry     

微孔发泡聚乳酸/木纤维复合材料的泡孔结构

引言聚乳酸(PLA)因具有环境友好性和降解性而被用于制备不同泡孔结构的泡沫制品[1],然而PLA呈现低的熔体强度和窄的加工窗口,这不利于以超临界流体(如超临界二氧化碳Sc-CO2)发泡制备微孔PLA材料[2-3]。加入填料(如二氧化硅[4]、羟基磷灰石[5]和蒙脱土[6]等)可改善PLA     

Influence of ammonium polyphosphate on the flame retardancy and mechanical properties of ramie fiber‐reinforced poly(lactic acid) biocomposites

Fully degradable natural fiber/degradable polymer composites have received much research attention and have various applications such as in automotive components. But flammability limits their application; it is important to improve the flame retardancy of fully degradable composites with environmentally friendly flame retardants. Flame‐retarded ramie fiber‐reinforced poly(lactic acid) (PLA) composites were prepared using three processes: (1) PLA was blended with ammonium polyphosphate (APP), and then the resulting flame‐retarded PLA was combined with ramie fibers; (2) ramie fibers underwent flame‐retardant treatment with APP, which were then compounded with PLA; and (3) PLA and ramie, both of which had been flame‐retarded using APP, were blended together. The APP in the composites is shown to be very effective in improving flame retardancy according UL94 test and limiting oxygen index measurements. Thermogravimetric analysis shows that the improved flame retardancy is due to increased char residue at high temperature. The loading of APP disturbs the compatibility between PLA and fibers, which can be directly observed using scanning electron microscopy. Furthermore it has an influence on the dynamic mechanical properties and mechanical properties according dynamic mechanical analysis and mechanical measurements. The results show that composites produced using the third process not only have the best flame retardancy but also comparatively better mechanical properties. Copyright © 2009 Society of Chemical Industry     

Preparation and some properties of stereocomplex‐type poly(lactic acid)/layered silicate nanocomposites

Stereocomplex‐type poly(lactic acid)‐ [PLA]‐ based blends were prepared by solution casting of equimolar PLLA/PDLA with different amounts of organo‐modified montmorillonite. The homocrystallization and stereocomplexation of PLAs were enhanced by annealing of the blends. The stereocomplexation of PLAs, intercalation of the polymer chains between the silicates layers, and morphological structure of the filled PLAs were analyzed by wide‐angle X‐ray diffraction and transmission electron microscope. Thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and tensile test were performed to study the thermal and mechanical properties of the blends. The homo‐ and stereocomplex crystallization of neat PLLA/PDLA were enhanced by annealing. The effect of annealing on the crystallization was emphasized by the addition of clay. With this structural change, thermal stabilities properties were also improved by the addition of clay. The silicate layers of the clay were slightly stacked but intercalated and distributed in the PLA‐matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fracture toughness of poly(lactic acid)/ ethylene acrylate copolymer/wood‐flour composite ternary blends

A fracture mechanics analysis based on the J‐integral method was adopted to determine the resistance of composites with various concentrations of wood‐flour and ethylene acrylate copolymer (EAC) to crack initiation (J_in) and complete fracture (J_f). The J_in and J_f energies of unmodified poly(lactic acid) (PLA)/wood‐flour composites showed the deleterious effect of incorporating wood fibers into the plastic matrix by significantly decreasing the fracture toughness of PLA as the wood‐flour content increased. The reduced fracture toughness of the matrix induced by adding brittle wood‐flour into PLA was well recovered by impact modification of the composites with EAC. Microscopic morphological studies revealed that the major mechanisms of toughening were through the EAC existing as separate domains in the bulk matrix of the composites which tended to act as stress concentrators that initiated local yielding of the matrix around crack tips and enhanced the toughness of the composites. © 2012 Society of Chemical Industry     

Reactable versus soluble DOPO derivatives in poly(lactic acid)/poly(butylene adipate-co-terephthalate) composites: Flame retardance,mechanical properties and morphology

Flame retardant poly(lactic acid)/poly(butylene adipate-co- terephthalate) (PLA/PBAT) composites containing 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO) derivatives (phosphorus-containing diol compound of DOPO-HQ, and bis DOPO phosphonates of DIDOPO) were systematically and comparatively investigated. Results showed that the different structures of the two derivatives with reactable or soluble characteristics display different effects. DIDOPO endows a higher limiting oxygen index and a better UL-94 rating for PLA/PBAT composites compared with DOPO-HQ. Compared with that of PLA/PBAT, the peak heat release rate of PLA/PBAT/DIDOPO-12.5 is 8.4% lower and that of PLA/PBAT/DOPO-HQ-12.5 is 30.6% lower. The flame retardant mechanism of the main gaseous and minor condensed phases is evident for the flame retardant PLA/PBAT composites. In comparison, DIDOPO displays a greater flame inhibition effect, and DOPO-HQ shows better barrier and protective functions in PLA/PBAT composites. Besides, the elongation at break of the composites with DOPO-HQ is slightly superior to that of PLA/PBAT/DIDOPO. After the introduction of flame retardant, the blends show dispersed particles with size reduction relative to those of PLA/PBAT. This work provides a guidance to design PLA composites with simultaneously improved flame retardancy and toughness.     

Dynamic mechanical and thermal properties of plasticized poly(lactic acid)

The blends of low molecular weight triacetin (TAC) and oligomeric poly(1,3‐butylene glycol adipate) (PBGA) were used as multiple plasticizers to lubricate poly(lactic acid) (PLA) in this study. The thermal and mechanical properties of plasticized polymers were investigated by means of dynamic mechanical analysis and differential scanning calorimetry. Atomic force microscopy (AFM) was used to analyze the morphologies of the blends. Multiple plasticizers were effective in lowering the glass transition temperature (T_g) and the melting temperature (T_m) of PLA. Moreover, crystallinity of PLA increased with increasing the content of multiple plasticizers. Tensile strength of the blends decreased following the increasing of the plasticizers, but increased in elongation at break. AFM topographic images showed that the multiple plasticizers dispersed between interfibrillar regions. Moreover, the fibrillar crystallite formed the quasicrosslinkings, which is another cause for the increase in elongation at break. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1583–1590, 2006     

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     

聚乳酸/聚乙烯醇纳米纤维的制备及结构

以二甲基亚砜为溶剂,制备不同配比的聚乳酸(PLLA)和聚乙烯醇(PVA)的混合溶液,静电纺丝制得PLLA/PVA纳米纤维。采用红外光谱仪、原子力显微镜等对PLLA/PVA纳米纤维结构与性能进行了表征。结果表明:PLLA/PVA纳米纤维中PVA上的羟基与PLLA上的羰基形成了氢键,PLLA与PVA之间存在一定的相互作用,但PLLA/PVA纳米纤维存在相分离现象;混合溶液的PLLA质量分数为11%,PVA质量分数为8%时可以得到较好的PLLA/PVA纳米纤维,但PVA质量分数为6%时出现液滴及珠丝,PVA质量分数为4%时,不能制得纳米纤维。     

Thermal properties and non‐isothermal crystallization behavior of poly(trimethylene terephthalate)/poly(lactic acid) blends

Thermal properties and non‐isothermal melt‐crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(lactic acid) (PLA) blends were investigated using differential scanning calorimetry and thermogravimetric analysis. The blends exhibit single and composition‐dependent glass transition temperature, cold crystallization temperature (T_cc) and melt crystallization peak temperature (T_mc) over the entire composition range, implying miscibility between the PLA and PTT components. The T_cc values of PTT/PLA blends increase, while the T_mc values decrease with increasing PLA content, suggesting that the cold crystallization and melt crystallization of PTT are retarded by the addition of PLA. The modified Avrami model is satisfactory in describing the non‐isothermal melt crystallization of the blends, whereas the Ozawa method is not applicable to the blends. The estimated Avrami exponent of the PTT/PLA blends ranges from 3.25 to 4.11, implying that the non‐isothermal crystallization follows a spherulitic‐like crystal growth combined with a complicated growth form. The PTT/PLA blends generally exhibit inferior crystallization rate and superior activation energy compared to pure PTT at the same cooling rate. The greater the PLA content in the PTT/PLA blends, the lower the crystallization rate and the higher the activation energy. Moreover, the introduction of PTT into PLA leads to an increase in the thermal stability behavior of the resulting PTT/PLA blends. Copyright © 2011 Society of Chemical Industry     

Properties of mineral filled poly(lactic acid)/poly(methyl methacrylate) blend

This study examines the influence of three different minerals, that is, clay, calcium carbonate, and quartz on the physical, thermal, and mechanical properties of poly(lactic acid) (PLA)/poly(methyl methacrylate) blend. Rheological behavior and phase structure were initially studied by small-amplitude oscillatory shear rheology. Clay- and quartz-filled materials presented an increase in viscosity at low frequency associated with the presence of a yield stress. However, this behavior was not observed for calcium carbonate filled materials due to a matrix degradation effect. To elucidate this aspect, thermal stability and thermal properties were examined by thermogravimetric analysis and differential scanning calorimetry, showing that calcium carbonate promotes degradation of the PLA phase. No nucleating effect was observed in the presence of the minerals. Dynamical mechanical analysis and mechanical characterization revealed an increase of the overall softening temperature and, a reinforcing effect for clay- and quartz-based composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46927.     

An investigation of melt rheology and thermal stability of poly(lactic acid)/ poly(butylene succinate) nanocomposites

A systematic investigation of the rheological and thermal properties of nanocomposites prepared with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and organically modified layered silicate was carried out. PLA/PBS/Cloisite 30BX (organically modified MMT) clay nanocomposites were prepared by using simple melt extrusion process. Composition of PLA and PBS polymers were fixed at a ratio of 80 to 20 by wt % for all the nanocomposites. Rheological investigations showed that high clay (> 3 wt %) contents strongly improved the viscoelastic behavior of the nanocomposites. Percolation threshold region was attained between 3 and 5 wt % of clay loadings. With the addition of clay content for these nanocomposites, liquid‐like behavior of PLA/PBS blend gradually changed to solid‐like behavior as shown by dynamic rheology. Steady shear showed that shear viscosity for the nanocomposites decreased with increasing shear rates, exhibiting shear‐thinning non‐Newtonian behavior. At higher clay concentrations, pseudo‐plastic behavior was dominant, whereas pure blend showed almost Newtonian behavior. Thermogravimetric analysis revealed that both initial degradation temperature (at a 2% weight loss) and activation energy of thermal decomposition nanocomposite containing 3 wt % of C30BX were superior to those of other nanocomposites as well as to those of PLA/PBS blend. Nanocomposite having 1 wt % of C30BX did not achieve expected level of thermal stability due to the thermal instability of the surfactant present in the organoclay. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

聚（乳酸⁃乙醇酸）薄膜制备及其性能研究

以左旋乳酸（L?LA）和乙醇酸（GA）为原料,利用一步法熔融共聚合成聚（乳酸?乙醇酸）（PLLGA）共聚物,通过差示扫描量热仪（DSC）对共聚物薄膜的结晶性能进行了表征,并利用Avrami方程对其进行了等温结晶动力学研究,通过万能拉伸试验机和压差法气体透过仪对共聚物薄膜的力学性能和气体阻隔性能进行测试。结果表明,PLLGA共聚物薄膜中GA的引入对材料结晶性能有较大影响,在GA含量为4 %（摩尔分数,下同）的PLLGA中,GA表现为成核剂作用,共聚物结晶比纯聚左旋乳酸（PLLA）薄膜快,半结晶时间减少;而在GA含量为8 %的PLLGA中,GA则表现出限制分子链运动的作用,破坏共聚物分子间的规整度,导致材料结晶性能大幅度降低,处于非晶态;随着GA含量的增加,PLLGA薄膜的拉伸强度和弹性模量逐步下降,而断裂伸长率大幅度增加,GA含量为8 %的PLLGA的断裂伸长率达到了130.1 %,是纯PLLA薄膜的21.3倍;同时,PLLGA薄膜的气体阻隔性显著增加,5 ℃时,相比于纯PLLA薄膜,GA含量为8 %的PLLGA薄膜的O₂、CO₂、N₂透过量分别降低了47 %、41 %和39 %。     

Effect of cooling conditions on the mechanical properties of crystalline poly(lactic acid)

Appropriate cooling conditions in melt processing were found to provide crystalline poly(lactic acid) (PLA) with greater mechanical toughness in tensile tests. PLA films cooled near its glass transition temperature T_g showed ductile behavior, whereas those obtained by a quenching process exhibited brittle fracture. The content of gauche‐gauche (gg) conformer, which leads to low critical onset stress for shear yielding, increased in the films cooled near T_g. The crystallinity of the films hardly affected their mechanical toughness and proportion of gg conformer except for that with a high degree of crystallinity (>50%). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44960.     

Influence of high loaded wood flour and coupling agent (m-TMI-g-PP) content on properties of wood flour/polypropylene

The effects of wood flour content (60–80%) and m-TMI-g-PP content (0–14%) on the properties of wood flour/polypropylene composites (WF/PP) were investigated by means of mechanical properties, thermal analysis, dynamic rheological analysis, and scanning electron microscopy (SEM). The results demonstrated that WF significantly increased the mechanical properties, char yield, heat deflection temperature (HDT), vicat softening temperature (VST), T _c, G′, G″, and η ^?. However, WF above 70% led to decreased mechanical properties, so for the comprehensive consideration of the cost and environmental issues, 70% WF is the best. With the addition of m-TMI-g-PP, the mechanical properties, thermal stability, HDT, VST, △H _m, and T _m of composites were all got improvement, which was attributed to the strong interfacial interaction of m-TMI-g-PP on composites. However, when it exceeded 10%, the mechanical properties of the composites declined, it probably formed a separate phase in the PP matrix. Therefore, the 10% m-TMI-g-PP was chosen in WF/PP. In addition, the results were all further confirmed by SEM analysis.     

聚乳酸及其纤维的发展概况和应用前景

介绍了聚乳酸及其纤维的发展现状,纺丝成型及纤维的性能和主要应用领域。由于聚乳酸纤维采用了天然可再生的植物资源,使用后可自然降解,所以在纺织、医学、农业等领域都有广阔的发展前景。