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Thermal degradation behavior and kinetics of starch/PLA composites in an inert and oxygen atmosphere were investigated by TG and TG-FTIR techniques. It is shown that the thermal degradation process can be divided into three stages, and a significant difference between thermal and thermo-oxidative degradation is the third stage in which the residual chars are further cracked for the thermo-oxidative degradation. The activation energy was calculated using the iso-conversional Flynn-Wall-Ozawa (FWO) method. The lower activation energy for thermo-oxidative degradation indicated that oxygen had an accelerated effect on thermal degradation. The variation of activation energy indicated that the decomposition of all the samples was a complex process that included at least two different mechanisms. Evolution of the evolved gaseous products with temperature was studied to understand the thermal and thermo-oxidative decomposition comprehensively. According to the TG-FTIR analysis, the gaseous products mainly contained lactide, cyclic oligomers, aldehydes, CO 2 , CO, and H 2 O., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A comparative study of the thermal behavior of PLA/starch blends annealed at different temperatures has been conducted. Annealing was found to be beneficial to weaken and even eliminate the enthalpy relaxation near Tg. The degree of crystallinity was evaluated by means of DSC, and the results showed that the crystallinity of the samples increased as the annealing temperatures were increased. It was observed that, during the annealing process, the disorder α (α') crystal modification tended to transform into the order α crystal modification. All of the PLA/starch blends showed a double melting behavior. With the increase of annealing temperatures, the lower Tm1 increased, while the Tm2 showed no evident change. The XRD patterns also showed that annealing was beneficial to the samples to form higher crystallinity. The TGA results indicated that the annealed samples did not show any higher thermal stability than the virgin samples. The activation energy calculated by the Flynn-Wall-Ozawa method at lower conversion degrees confirmed that the annealing slightly slowed the degradation. The activation energy did not show any dependence on the conversion degree, which indicated that there existed a complex degradation process of the PLA/starch blends. The average activation energy did not show obvious differences, indicating that the annealing treatment had little influence on the degradation activation energy., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Maleic anhydride esterified corn starch was prepared by dry method. Esterified starch/polylactic acid (PLA) biodegradable composite was produced via melt extrusion method with blending maleic anhydride esterified corn starch and PLA. The influence of the dry method esterification of starch on the degradation characteristics of starch/PLA composites was investigated by the natural aging degradation which was soil burial method. Test results of mass loss rate showed that the first 30 days of degradation was mainly starch degradation, and the degradation rate of esterified starch/PLA (ES/PLA) was slower than that of native starch/PLA (NS/PLA). Therefore, the damage degree of ES/PLA on the surface and inside was smaller than that of NS/PLA, and the infrared absorption peak intensities of C-O, C=O and C-H were stronger than that of NS/PLA. With the increasing time of soil burial degradation, the damage degree of NS/PLA and ES/PLA on the exterior and interior were gradually increased, whereas the infrared absorption peak intensities of C-O, C=O and C-H were gradually decreased. The XRD diffraction peak intensity of PLA in composites showed an increased trend at first which was then followed by a decreased one along with the increasing time of soil burial degradation, indicating that the degradation of amorphous regions of PLA was earlier than its crystalline regions. When the soil burial time was the same, the diffraction peak intensity of PLA in ES/PLA was stronger than that of NS/PLA. If the degradation time was the same, T0, Ti and residual rate of thermal decomposition of NS/PLA were larger than those of ES/PLA. The tensile strength and bending strength of composites were decreased gradually with soil burial time increasing. Both the tensile strength and bending strength of ES/PLA were stronger than those of NS/PLA., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Corn starch and maleic anhydride were synthesized from a maleic anhydride esterified starch by dry method. Fourier transform infrared spectroscopy (FTIR) was used for the qualitative analysis of the esterified starches. The reaction efficiency of dry method esterified starch reached 92.34%. The dry method esterified starch was blended with polylactic acid (PLA), and the mixture was melted and extruded to produce the esterified starch/polylactic acid (ES/PLA) composites. The degree of crystallinity of the ES/PLA was lower than that of the NS/PLA, indicating that the relative dependence between these two components of starch and polylactic acid was enhanced. Scanning electron microscopy (SEM) indicated that the dry method esterified starch increased the two-phase interface compatibility of the composites, thereby improving the tensile strength, bending strength, and elongation at break of the ES/PLA composite. The introduction of a hydrophobic ester bond and increase in interface compatibility led to an increase in ES/PLA water resistance. Melt index determination results showed that starch esterification modification had improved the melt flow properties of starch/PLA composite material. Strain scanning also showed that the compatibility of ES/PLA was increased. While frequency scanning showed that the storage modulus and complex viscosity of ES/PLA was less than that of NS/PLA., (Copyright © 2013 Elsevier B.V. All rights reserved.)

In recent years, under the pressure of resource shortage and white pollution, the development and utilization of biodegradable wood-plastic composites (WPC) has become one of the hot spots for scholars' research. Here, corn straw fiber (CSF) was chosen to reinforce a poly(lactic acid) (PLA) matrix with a mass ratio of 3:7, and the CSF/PLA composites were obtained by melt mixing. The results showed that the mechanical properties of the corn straw fiber core (CSFC) and corn straw fiber skin (CSFS) loaded PLA composites were stronger than those of the CSFS/PLA composites when the particle size of CSF was low. The tensile strength and bending strength of CSFS/CSFC/PLA are 54.08 MPa and 87.24 MPa, respectively, and the elongation at break is 4.60%. After soaking for 8 hours, the water absorption of CSF/PLA composite reached saturation. When the particle size of CSF is above 80 mesh, the saturated water absorption of the material is kept below 7%, and CSF/PLA composite has good hydrophobicity, which is mainly related to the interfacial compatibility between PLA and CSF. By observing the microstructure of the cross section of the CSF/PLA composite, the research found that the smaller the particle size of CSF, the smoother the cross section of the composite and the more unified the dispersion of CSF in PLA. Therefore, exploring the composites formed by different components of CSF and PLA can not only expand the application range of PLA, but also enhance the application value of CSF in the field of composites. [ABSTRACT FROM AUTHOR]

Green and renewable foaming poly(lactic acid) (PLA) represents one of the promising developments in PLA materials. This study is the first to use the lignin graft PLA copolymer (LG‐g‐PLA) to improve the foamability of PLA as a biobased nucleating agent. This agent was synthesized via ring‐opening polymerization of lignin and lactide. The effects of LG‐g‐PLA on cell nucleation induced by the crystallization, rheological behavior, and foamability of PLA were evaluated. Results indicated that LG‐g‐PLA can improve the crystallization rate and crystallinity of PLA, and play a significant nucleation role in the microcellular foam processing of PLA. LG‐g‐PLA improved the foam morphology of PLA, obtaining a reduced and uniform cell size as well as increased expansion ratio and cell density. With the addition of 3 wt% LG‐g‐PLA content, the PLA/LG‐g‐PLA foams increased the compressive strength 1.6 times than that of neat PLA foams. The improved foaming properties of PLA via a biobased nucleating agent show potential for the production and application of green biodegradable foams. [ABSTRACT FROM AUTHOR]

The difficulty of dispersing cellulose nanocrystals (CNCs) in poly(lactic acid) (PLA) was still a primary obstacle to enhance the properties of PLA nanocomposites. In this work, two different methods were used to modify CNCs that were then added dropwise and mixed with the PLA solution to conveniently obtain the composites. Transmission electron microscopy and Fourier transform infrared spectroscopy were used to characterize CNCs before and after modification. Ultraviolet–visible spectroscopy, tensile tests, differential scanning calorimetry, and thermogravimetric analysis were used to characterize the PLA nanocomposites. The results revealed that the CNCs that were modified with surfactant had better dispersion and thermal stability in the PLA nanocomposites. The Young's modulus and strength of PLA/SCNC nanocomposites were significantly reinforced (up to 66.0% and 29.8%, respectively). Meanwhile, the transmittance remained above 60% in the visible range. The solution precipitation approach was effective and simple, which could be used with other polymers. [ABSTRACT FROM AUTHOR]

To prolong the service lives of wood fiber (WF)/poly(lactic acid) (PLA) composites, composites with different contents of bis (2,6-diisopropylphenyl) carbodiimide (BDICDI) were prepared. The composites were buried in natural soil for 150 days to evaluate the stabilizing effect of BDICDI on the WF/PLA composites. It was also used to evaluate the properties changes of WF/PLA composites under extreme conditions. The changes in the chemical structures, molecular weights and thermal properties of the WF/PLA composites during soil burial and the stabilization mechanism of BDICDI on the composites were studied. The results showed that the addition of BDICDI reacted with both the formed acid and the water absorbed by the WF/PLA composites, which inhibited the breaking of ester bonds in the WF/PLA composites. After 120 days of soil burial, the tensile strengths of the WF/PLA/1 wt% BDICDI composites were 1.31 times to those of the WF/PLA composites. This research provided theoretical support to prolong the service lives of WF/PLA composites and expanded the application scope of WF/PLA composites. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Abstract Plastic pollution is a major environmental problem and the waste disposal is a challenge in this case. Poly (lactic acid) (PLA) based biodegradable materials is one of the most attractive polymers which can fulfill the current demand. In this work, the degradation of starch/PLA composite was investigated in real soil environment. The weight loss results demonstrated that the degradation rate of PLA could be accelerated by starch. Scanning electrical microscopy (SEM) and Fourier transform infrared (FTIR) results showed that the samples degraded faster with the presence of starch. The mechanical strengths had an abrupt decrease for the starch/PLA composite while that of PLA only decreased in a low degree. The distribution of carboxyl group intensity and carbon atomic percent reflected the heterogeneity of biodegradation for starch/PLA composite in soil. Moreover, the variation of internal carbon atomic percent was higher than that on the surface, demonstrating that the degradation of starch/PLA composite was bulk degradation. Based on the role of starch played in starch/PLA composite and the physicochemical performance evolutions during biodegradation, it should create a scientific basis for people interested in studying the biodegradation of PLA, and provide some knowledge about controlling the biodegradation rate of PLA through adjusting the content of starch in the composite. Graphical abstract Image Highlights • Starch can accelerate the biodegradation rate of PLA in soil. • Both the biodegradation of PLA and starch/PLA composite were heterogeneous. • Both the PLA and starch/PLA composite underwent bulk degradation. [ABSTRACT FROM AUTHOR]

Plasticized poly (lactic acid) (PPLA) was prepared by melt blending poly (lactic acid) (PLA) with 10 wt% of poly (ethylene glycol) (PEG), with varied molecular weights range from 400 to 4000. The structure, thermal property, morphology, and surface free energy of the PPLA were investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and contact angles (CA). The resulting PPLA results indicated that the introduction of PEG to the blend systems resulted in a ductile fracture, a decrease in the melt temperature (Tm) and glass transfer temperature (Tg), and an increase in the degree of crystallization (χc), which indicated an improved flexibility. In addition, the polarity of the PPLA increased and the surface free energy decreased. The resulting PPLA was subsequently used as matrix to blend with wood flour to prepare composites. The mechanical strength, melting behavior, thermal stability, and microscopy of the PPLA/wood flour composites were also evaluated. These results illustrated that the plasticized PPLA matrix was beneficial to the interfacial compatibility between the polar filler and the substrate. [ABSTRACT FROM AUTHOR]

The biodegradation behavior of Poly (lactic acid) (PLA) blended with starch and wood flour in outdoor soil was investigated comprehensively. As a result, starch provided a biological fuel for the growth of microorganisms in the soil which accelerated the degradation rate of PLA more obviously than wood flour. With the increase of starch content, the weight loss increased and the morphology exhibited more gullies and cavities. X-ray Photoelectron Spectroscopy (XPS) analysis indicated that the variation of O/C ratio was controlled by starch biodegradation and PLA hydrolysis and they were a concomitant process. The mechanical strengths of all the blends showed similar trend and fitted a first-order exponential decay model. The model is shown in good agreement with experimental results as the correlation coefficient is higher than 0.99, and the model can support an efficient method to estimate the durability of starch/wood flour/PLA blends. [ABSTRACT FROM AUTHOR]

The high density and poor thermal insulation of traditional wood-plastic composites limited the application in the field of building materials. In this paper, wood fiber (WF) and PLA were used as raw materials and azodicarbonamide was used as the foaming agent. Lightweight WF/PLA composites were prepared by the hot-pressing foaming method, aiming to obtain renewable, low-density material with high strength-to-weight ratio and thermal insulation performance. The results showed that after adding 20 % WF into PLA, the cell morphology was excellent and the cell size was uniform. The magnification reached the minimum value of 0.36 g/cm3 and the foaming magnification was 3.42 times. The impact strength and compressive strength were 3.16 kJ/m3 and 4.12 MPa, its comprehensive mechanical properties were outstanding. The thermal conductivity of foamed materials was 0.110–0.148 (W/m·K), which was significantly lower than that of unfoamed materials and common wood. Its excellent mechanical properties and thermal insulation can be suitable for application in the construction field to replace traditional wood. [Display omitted] • Preparation of renewable and lightweight wood fiber/poly(lactic acid) composites • The composites have high mechanism strength and thermal insulation performance. • Wood flour content can affect the lightweight material properties. [ABSTRACT FROM AUTHOR]

Herein, carvacrol (CRV) and modified cellulose nanocrystal–zinc oxide (CNC–ZnO) were incorporated into a poly (lactic acid) (PLA) matrix to prepare a PLA-based composite film using a simple solution casting method to achieve antimicrobial effects for application in antimicrobial food packaging. Compared with films obtained from neat PLA, the PLA@CRV 20% @CNC–ZnO 3% composite film shows better performance in terms of mechanical properties, ultraviolet (UV) blocking, and antimicrobial effects. The PLA composites containing CRV and 3 wt% CNC–ZnO blends exhibit improved tensile strength (21.8 MPa) and elongation at break (403.1 %) as well as excellent UV resistance. In particular, CRV and the CNC–ZnO hybrid endow the obtained PLA composite films with a synergistic antibacterial effect, resulting in good antibacterial properties for microbes, such as Escherichia coli , Staphylococcus aureus and Aspergillus niger. The diameters of the inhibition zone of the PLA@CRV 20% @CNC–ZnO 3% composite films against E. coli , S. aureus , and A. niger were 4.9, 5.0, and 3.4 cm, respectively. Appling the PLA@CRV 20% @CNC–ZnO 3% composite film as an antibacterial food packaging material, the storage period for strawberries was considerably extended. This study provides a theoretical basis for developing new organic/inorganic composite antimicrobial film materials from PLA. [Display omitted] • A dual organic (CRV)/inorganic (CNC–ZnO) synergistic antibacterial mechanism was found. • The PLA@CRV 20% @CNC–ZnO 3% composite film exhibited excellent antimicrobial activity. • The composite film can effectively extend the shelf life of strawberries up to 12 days. [ABSTRACT FROM AUTHOR]

Biodegradable poly (lactide) (PLA) and poly (butylene adipate- co -terephthalate) (PBAT) composite films were made by a co-precipitation and hot-pressing method. The property of composite films like the chemical interaction, phase morphology, mechanical properties, and thermal properties were studied. The Fourier transform infrared spectroscopy (FTIR) test manifested that there was a small amount of the transesterifications between the PBAT and PLA during hot pressing, which could improve the compatibility of the two phases. The tensile strength of the film only reduced by 7.4%, while the elongation at break was increased by 119.1% compared with PLA after adding 4%wt PBAT. The composite films showed a high Ultraviolet-visible (UV) light barrier property. The UV blocking rate of the composite after adding 4%wt PBAT was 6.95 times higher than that of pure PLA at 380 nm. The PLA/PBAT composite films with excellent thermal stability, satisfactory mechanical properties and UV-light barrier have high a possibility for an UV screening packaging application. [Display omitted] • The PLA/PBAT composite films made by a co-precipitation method • The transesterification between the PBAT and PLA has existed. • The PBAT at low addition levels blended with PLA can realize the compatibility. [ABSTRACT FROM AUTHOR]

Using polylactic acid (PLA) as the green wall insulation materials have the advantages of environmental protection and renewable, but they are not widely used due to poor performance. To solve this problem, azodicarbonamide (AC) used as the foaming agent and PLA/rice straw (RS) bio-composite foams were processed using the moulded foaming method. And degradable polycaprolactone (PCL) was added to improve the performance of foams. After the addition of 40 wt% PCL, the impact strength, compression strength and water resistance of the foams were improved by 357.7 %, 277.1 % and 803.9 %, respectively. All foams exhibited excellent insulation performance of 0.038–0.040w/(m·k). Thus, this study provides an effective way to resource utilization of crop waste and prepare high-performance wall insulation foam materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • PLA can be burned as a fuel because the incineration is regard as carbon neutral. • Pyrolysis of PLA with MgO and its co-pyrolysis with biomass is very promising. • Alcoholysis of PLA is considered to be the most suitable method for chemical recovery of PLA. • The hydrolysis of PLA can upcycle lactic acid with low energy consumption compared to that from starch fermentation. • The products have higher added value and wider usages during ammonolysis of PLA. Polylactic acid (PLA) is currently the highest production of all bio-based plastics globally. Its production will increase year by year to replace part of petroleum-based plastics to reduce environmental pollution and curb carbon emissions. However, the raw materials for synthesizing PLA mainly come from sugary foods, and mass production will pose a threat to food security. In addition, the degradation rate of PLA is slow, and a large amount of waste PLA accumulation still causes pollution. As a high-quality carbon source, compared with direct degradation, recycling PLA is a more green and environmentally friendly method. Because PLA can not only be depolymerized into raw materials for synthesizing PLA but also can be upcycled to chemicals required by various industries, which helps to reduce the use of petroleum resources. In addition, the recycling of PLA helps to reduce CO 2 emissions, because the source of PLA does not consume petroleum resources, but rather fixes CO 2 in the air. This review summarizes the works of upcycling waste PLA as an alternative carbon source for energy and other chemicals from the perspectives of tertiary and quaternary recycling, which provides a reference for the proper treatment of a large amount of waste PLA. [ABSTRACT FROM AUTHOR]

[Display omitted] • Time-dependent hydrolysis behavior of PLA and starch/PLA composites were studied. • Starch slightly slowed down the hydrolysis of PLA, but did not reduce the final hydrolytic degree. • The autocatalysis effect was more prominent at a higher temperature. Structural modification of starch/PLA composites caused by hydrolysis was evaluated at different temperatures. Water uptake of starch/PLA composites showed a time-dependent behavior which did not follow the Fickian behavior well. Molecular weight also showed a time dependence, especially at 50 °C. Combining water uptake and molecular weight change together, the entrapment of acidic products in the bulk could increase the hydrophilicity of materials and catalyze the hydrolysis. The chain scission occurred at the C = O in the PLA chains according to the FTIR results. The presence of starch may induce the hydrolysis to take place at the interface between starch and PLA matrix. In addition, starch may slow down the hydrolysis rate slightly without influencing the hydrolysis degree. This research should provide valuable information for designing green materials to be applied in water-present conditions. [ABSTRACT FROM AUTHOR]