ABSTRACT Lignin and agricultural residues are promising resources for wood adhesives, but the use of tobacco stem powder ( TSP ) in phenolated lignin‐based phenol–formaldehyde ( PF ) adhesives remains little studied. Phenolated kraft lignin‐based PF ( PKL ‐ PF ) resin was prepared, and TSP partially replaced concentrated resin solution at constant spread. L 9 orthogonal designs optimized resin synthesis and hot‐pressing. At the selected pressing conditions (140°C, 140 g m −2 , 9 min), dry strength peaked at 10 wt% TSP (4.63 ± 0.72 MPa ), significantly exceeding the TSP ‐free control (3.52 ± 0.35 MPa ). Wet strength was highest at 15 wt% TSP (4.42 ± 0.73 MPa ), but did not differ significantly from the control (4.17 ± 0.47 MPa ). After boiling‐water treatment, 15 wt% TSP gave the highest bonding strength (3.60 ± 0.46 MPa ), whereas 12 wt% TSP had the highest wood failure percentage (74.00% ± 13.42%).
ABSTRACT Traditional epoxy resin (EP) grouting materials are hindered by high brittleness, excessive shrinkage, and slow curing. To address these issues, a polyurethane/epoxy (PU‐EP) interpenetrating polymer network (IPN) composite was developed using a two‐component isocyanate system (MDI/IPDI). At the optimal PU‐EP mass ratio of 10:90, the material exhibited an initial viscosity of 218 mPa·s, a setting time of 18 min, and a volume shrinkage of only 1.75%. Compared with pure EP, tensile, compressive, impact, and flexural strengths increased by 30%, 21%, 54%, and 15%, respectively, with an adhesive strength of 4.29 MPa. Microscopic analyses revealed a well‐developed IPN structure with ductile fracture features and uniformly distributed microbubbles that relieved internal stress. Thermal stability remained adequate up to 150°C. Field tests confirmed rapid crack filling (5 mm wide, 200 mm deep) within 2 min, with no secondary cracking after 30 days and a core compressive strength of 66 MPa. This composite offers a balanced combination of low viscosity, fast curing, high strength, and low shrinkage, making it suitable for rapid concrete crack repair.
ABSTRACT The development of low‐gloss waterborne polyurethane coatings for Polyvinyl Chloride (PVC) artificial leather finishing without external matting agents remains challenging. In this work, self‐matting waterborne polyurethane (SMWPU) dispersions were synthesized by the prepolymer method using Polytetramethylene ether glycol (PTMG‐2000), Isophorone diisocyanate (IPDI), Dimethylolpropionic acid (DMPA), and Trimethylolpropane (TMP). The effects of the isocyanate index ( R value), DMPA content, and TMP content on particle size, Zeta potential, dispersion stability, thermal stability, surface morphology, and gloss were systematically investigated. Increasing the R value increased particle size and surface roughness, reducing gloss from 3.18 to 2.67. Increasing DMPA content enhanced surface charge density and dispersion stability, with the lowest gloss of 2.65 at 1.8 wt% DMPA. Increasing TMP content increased crosslinking density and particle size, with the lowest gloss of 2.66 at 1.2 wt% TMP, while improving thermal stability. SEM analysis showed that particle size and distribution strongly affected surface morphology, and a uniformly rough surface was essential for effective self‐matting. These findings provide practical guidance for developing low‐gloss SMWPU coatings for PVC artificial leather finishing.
ABSTRACT A possible way to enhance the Z‐directional mechanical characteristics of laminated GFRP composites is by suitable through‐thickness alignment of secondary reinforcements. In this work, efficient alignment of polar carboxyl functionalized graphene (FG) in a laminated GFRP composite has been achieved by optimizing the applied z‐directional A.C. field strength. The laminate AF300, where the field strength is 300 V/mm exhibited the best flexural strength among all the composites considered, which is 17% and 32% higher over randomly oriented FG embedded GFRP (RF) and neat GFRP composites respectively. Dynamic mechanical analysis also suggests similar effect where the storage modulus of AF300 composite was found to be significantly better over both RF and Neat composites. Short beam strength as obtained indicates efficient restriction towards delamination due to the through‐thickness alignment of FG. A substantial improvement in energy absorption during Mode I inter laminar fracture toughness (ILFT) test has been noticed due to alignment of FG in the GFRP composite. Similarly, AF300 composite exhibited 84% better Mode II ILFT over the neat composite. Through thickness electrical conductance of AF300 composite is 350% better than Neat and 80% better then RF composite, indicating successful alignment of FG along through thickness direction.
ABSTRACT Compared with traditional thermal interface material (TIM) systems, the TIM‐free heat dissipation system proposed in the study removes the separate TIM layer by using a 3D‐printed monolithic structure, thereby reducing the number of thermal interfaces in the heat path. The integrated design allows for custom‐designed, lightweight, and compact structures directly printed onto heat sources, enhancing thermal management efficiency. In this study, we introduce a novel silicone‐based thermal conductive gel, named TIM‐free, achieving a thermal conductivity of up to 1.69 W m −1 K −1 , a total thermal resistance as low as 5.31 × 10 −4 m 2 K W −1 , a storage modulus as low as 392.8 Pa, and an elongation at break of up to 5.44%. Moreover, the TIM‐free gel exhibits excellent printability and can be directly written into 3D heat sink structures. In thermal management tests, the TIM‐free gel was printed directly onto ceramic heaters; compared with setups without any TIM, the temperature of the ceramic heater equipped with the printed TIM‐free heat sink was reduced by 10°C. This approach is particularly suitable for high‐power‐density, next‐generation electronics requiring efficient and space‐saving thermal solutions.
