Shanshan Lv

Biodegradation behavior and modelling of soil burial effect on degradation rate of PLA blended with starch and wood flour

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.

Preparation and properties of isocyanate prepolymer/corn starch adhesive

Utilizing corn starch as a main raw material to prepare starch adhesive, polyvinyl alcohol, borax, and carboxymethyl cellulose (CMC) were added in the preparation process. Because of the poor water resistance of native starch adhesive, an isocyanate prepolymer as a cross-linking agent was synthesized and added to improve its water resistance. Three-layer wood panels were fabricated and bonding strength was measured. The differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the thermal properties, morphology, and element content of samples. Effects of R value (the molar ratio of isocyanate group to hydroxyl group) and CMC addition on the physicochemical properties of starch adhesive were investigated. Thermal analysis results showed prepolymer/starch adhesive (PSA) cured at a relatively low temperature and thermal stability was improved after prepolymer added. SEM, XPS, and EDX results revealed that prepolymer played an effective role in bonding process, and the penetration of adhesive occurred in the wood, resulting in the improvement of bonding strength.

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

Abstract 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.

Effect of Mesh Number of Wood Powder and Ratio of Raw Materials on Properties of Composite Material of Starch/Wood Powder

Utilizing wood powder and corn starch as the main materials with polyurethane adhesive as a cross-linking agent, the starch/wood powder composite material was prepared via molding forming techniques. The effects of wood powder mesh and addition of wood powder on the properties of composite material were investigated. The compatibility of starch and wood powder and the thermal stability of composite were evaluated by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMA), respectively. The mechanical properties and water absorption of composite material were also tested. The results showed that the mechanical properties and water resistance of composite material first increased and then fell with increasing mesh, and the best performance was obtained when the mesh ranged from 80 to 100. The best compatibility, mechanical properties, water resistance, and thermal stability of composite material was obtained with 10% polyurethane crosslinking agent addition.

Soil burial-induced chemical and thermal changes in starch/poly (lactic acid) composites

Soil burial degradation was confirmed to be an efficient waste disposal method for the biodegradable materials with short service life, such as starch/poly (lactic acid) (PLA) composite. The biodegradation behavior about chemical and thermal properties of starch/PLA composite was analyzed by using X-ray photoelectron spectroscopy (XPS), infrared microscopy (IRM), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). XPS and IRM results indicated that the biodegradation of PLA occurred at the ester groups in PLA chains. XPS demonstrated the cleavage of CO linkages between glucose rings in starch. DSC and TGA results showed that the starch/PLA composite degraded faster than the pure PLA. During the soil burial degradation, the glass transition temperature of starch/PLA composite exhibited an obviously decrease while it had a slight variation for PLA. The thermal stability of starch/PLA composite shifted towards to that of PLA when they were subjected to soil burial for the same time. It is established that the starch can accelerate the degradation of PLA-based materials, which will enlarge the markets of biodegradable PLA materials used for short service life products.

Preparation of plasticized poly (lactic acid) and its influence on the properties of composite materials

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.

Transcriptomic analysis reveals the roles of gibberellin-regulated genes and transcription factors in regulating bolting in lettuce (Lactuca sativa L.)

A cool temperature is preferred for lettuce cultivation, as high temperatures cause premature bolting. Accordingly, exploring the mechanism of bolting and preventing premature bolting is important for agriculture. To explore this relationship in depth, morphological, physiological, and transcriptomic analyses of the bolting-sensitive line S39 at the five-leaf stage grown at 37°C were performed in the present study. Based on paraffin section results, we observed that S39 began bolting on the seventh day at 37°C. During bolting in the heat-treated plants, GA3 and GA4 levels in leaves and the indoleacetic acid (IAA) level in the stem reached a maximum on the sixth day, and these high contents were maintained. Additionally, bolting begins in the fifth day after GA3 treatment in S39 plants, GA3 and GA4 increased and then decreased, reaching a maximum on the fourth day in leaves. Similarly, IAA contents reached a maximum in the stem on the fifth day. No bolting was observed in the control group grown at 25°C, and significant changes were not observed in GA3 and GA4 levels in the controls during the observation period. RNA-sequencing data implicated transcription factors (TFs) in regulating bolting in lettuce, suggesting that the high GA contents in the leaves and IAA in the stem promote bolting. TFs possibly modulate the expression of related genes, such as those encoding hormones, potentially regulating bolting in lettuce. Compared to the control group, 258 TFs were identified in the stem of the treatment group, among which 98 and 156 were differentially up- and down-regulated, respectively; in leaves, 202 and 115 TFs were differentially up- and down-regulated, respectively. Significant changes in the treated group were observed for C2H2 zinc finger, AP2-EREBP, and WRKY families, indicating that these TFs may play important roles in regulating bolting.

Physicochemical evolutions of starch/poly (lactic acid) composite biodegraded in real soil

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.

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

Abstract 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.