Acetylated nanocellulose reinforced hydroxypropyl starch acetate realizing polypropylene replacement for green packaging application.

The use of natural starch as a replacement for petroleum-based packaging materials is limited due to its poor processability, weak mechanical properties, and strong moisture sensitivity. To address these limitations, this study adopts molecular design of hydroxypropylation and acetylation to sequentially modify natural starch, and material design of introducing acetylated cellulose nanofibers (ACNF) into the starch matrix to reinforce the material. Hydroxypropylation decreased the interaction force between the starch molecular chains, thereby reducing the glass transition temperature. Subsequent acetylation introduced hydrophobic acetyl groups that disrupted intermolecular hydrogen bonds, enhancing the mobility of the starch molecular chain, and endowed the hydroxypropyl starch acetate (HPSA) with excellent thermoplastic processability (melt index of 7.12 g/10 min) without the need for plasticizers and notable water resistance (water absorption rate of 3.0 %). The introduction of ACNF generated a strong interaction between HPSA chains, promoting the derived ACNF-HPSA to exhibit excellent mechanical strength, such as high impact strength of 2.1 kJ/m2, tensile strength of 22.89 MPa, elasticity modulus of 813.22 MPa, flexural strength of 24.18 MPa and flexural modulus of 1367.88 MPa. Its overall performance even surpassed that of polypropylene (PP) plastic, making it a potential alternative material for PP-based packaging materials.

Improvement of Mechanical Properties and Solvent Resistance of Polyurethane Coating by Chemical Grafting of Graphene Oxide.

Waterborne polyurethane coatings (WPU) are widely used in various types of coatings due to their environmental friendliness, rich gloss, and strong adhesion. However, their inferior mechanical properties and solvent resistance limit their application on the surface of wood products. In this study, graphene oxide (GO) with nanoscale size, large surface area, and abundant functional groups was incorporated into WPU by chemical grafting to improve the dispersion of GO in WPU, resulting in excellent mechanical properties and solvent resistance of WPU coatings. GO with abundant oxygen-containing functional groups and nanoscale size was prepared, and maintained good compatibility with WPU. When the GO concentration was 0.7 wt%, the tensile strength of GO-modified WPU coating film increased by 64.89%, and the abrasion resistance and pendulum hardness increased by 28.19% and 15.87%, respectively. In addition, GO also improved the solvent resistance of WPU coatings. The chemical grafting strategy employed in this study provides a feasible way to improve the dispersion of GO in WPU and provides a useful reference for the modification of waterborne wood coatings.

Acrylic Resin Filling Cell Lumen Enabled Laminated Poplar Veneer Lumber as Structural Building Material.

Wood is a viable alternative to traditional steel, cement, and concrete as a structural material for building applications, utilizing renewable resources and addressing the challenges of high energy consumption and environmental pollution in the construction industry. However, the vast supply of fast-growing poplar wood has bottlenecks in terms of low strength and dimensional stability, making it difficult to use as a structural material. An environmentally friendly acrylic resin system was designed and cured in this study to fill the poplar cell cavities, resulting in a new type of poplar laminated veneer lumber with improved mechanical strength and dimensional stability. The optimized acrylic resin system had a solid content of 25% and a curing agent content of 10% of the resin solid content. The cured filled poplar veneer gained 81.36% of its weight and had a density of 0.69 g/cm3. The static flexural strength and modulus of elasticity of the further prepared laminated veneer lumber were 123.12 MPa and 12,944.76 MPa, respectively, exceeding the highest flexural strength required for wood structural timber for construction (modulus of elasticity 12,500 MPa and static flexural strength 35 MPa). Its tensile strength, impact toughness, hardness, attrition value, water absorption, water absorption thickness expansion, and water absorption width expansion were 58.81%, 19.50%, 419.18%, 76.83%, 44.38%, 13.90%, and 37.60% higher than untreated laminated veneer lumber, demonstrating improved mechanical strength and dimensional stability, significantly. This method provides a novel approach to encouraging the use of low-value-added poplar wood in high-value-added structural building material applications.

Mechanical Properties and Dimensional Stability of Poplar Wood Modified by Pre-Compression and Post-Vacuum-Thermo Treatments.

Fast-growing poplar wood has the bottleneck problems of inferior mechanical strength and poor dimensional stability. In this study, the wood was modified by combined treatments of pre-compression and post-vacuum-thermo modification to improve its mechanical strength and dimensional stability, simultaneously; in addition, the variation law of mechanical properties of the wood with compression ratio as well as the improvement effect of dimensional stability of the treated wood were mainly studied. The results show that the optimal temperature and time of the vacuum-thermo modification were 190 °C and 10 h, respectively. Under these conditions, the structure of pre-compressed and post-vacuum-thermally modified wood (CT wood) is gradually densified with the increase in the compression ratio, which results in the continuous enhancement of mechanical properties. Meanwhile, the anti-swelling efficiency (ASE) of the CT wood after water absorption is correspondingly better than that of the compressed wood before thermal modification, indicating that the dimensional stability of compressed wood was improved by the thermal modification. When the compression ratio was 70%, the modulus of rupture (MOR) and impact toughness of CT wood was 176 MPa and 63 KJ/m2, which was 125% and 59% higher than that of untreated wood, respectively. The ASE was also 26% higher than that of the wood with sole compression. Therefore, this method improves the mechanical strength and dimensional stability of wood simultaneously, and it provides a scientific basis for optimization of the reinforcing modification process of fast-growing wood.