Chunping Dai
Research Classification
Research Interests
Relevant Thesis-Based Degree Programs
Research Methodology
Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
During the manufacturing of wood composites, mats of resinated fibers, particles or strands are consolidated under heat and pressure to produce panels with the necessary strength and stiffness properties. As the mat consolidates a vertical density profile (VDP) is established and it has a significant impact on panel properties. In order to tailor the VDP of the panel to various end-use applications, a means of describing of the effect of pressing variables on the development of the VDP is needed.This study examined the role of environmental factors, i.e., temperature and moisture content (MC), on the compression and viscoelastic behavior of wood strands. The strand stress-strain relationship during hot pressing was modeled using a modified Hooke’s law, in which the compression modulus as a function of temperature and MC was quantitatively obtained using a regression approach. Similarly, the viscoelastic behavior of strands was investigated for various temperatures and MCs and the results were used to develop a model for predicting the stress relaxation response of the strands. The results showed that the relaxation modulus as a function of time follows a linear relationship on a log-log plot; it is important to note that the response was affected by strain level and environmental conditions.Based on the strand compression properties and mat structure, a comprehensive model was established that simulated the VDP development and was found to be a good description of the experimental results. The effects of mat elastoplasticity and springback on the formation of the VDP were also discussed. In addition, a generalized model based on the beam bending of the wood elements was developed to predict the mat pressure-density relationship of wood composites. This is valuable for improving the fundamental understanding of the relationship between pressing variables and panel properties for process optimization.
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Sustainable development of bamboo-wood composites requires a better understanding and optimization of bonding. This thesis investigates the bonding process and performance of structural bamboo-wood laminates. A polylamellate cell wall structure, low tissue porosity and permeability, and poor surface wettability all hamper bamboo bonding with most softwood adhesives. Adhesive modification must be optimized in conjunction with more efficient material utilization and processes. Understanding the bonding mechanism between wood/bamboo and adhesives is essential for the development of modified adhesives for advanced hybrid composite. Phenol formaldehyde (PF) resins with two different molecular weights (MW) were tested for bamboo-wood bonding. Optical microscopy was used to observe the penetration of resin into the surface of solid or veneered wood (Douglas fir) and milled or flattened bamboo (Moso). The results showed that on the bamboo substrate, high MW PF largely remained in the glueline and only entered the lumina of cut or damaged cells near the bondline. Low MW PF penetrated cell wall corners of Moso bamboo but not the uncut lumens. Undamaged lumens seem impermeable to PF resins. Results from dry and wet bond shear tests showed that applying low MW PF to the bamboo and high MW PF to the wood surface separately significantly improved the bonding performance. The work also evaluated PF mixed with extenders and fillers for bonding veneer-type hybrid wood-bamboo composites with different glue application rates. The mixed plywood PF was comparable in both dry and wet bond shear strength and wood failure to using pure PF even at the same glue application rate due to its good gap filling capability. The findings indicate that plywood resin with fillers is a viable, lower cost-effective adhesive for veneer-type wood-bamboo composites.In conclusion, hybrid bamboo-wood composites are promising cost-effective approaches for the engineered bamboo industry, leading to viable building products. Bond qualification standards for wet bond criteria of plywood will need to be modified and adapted to accommodate the different resins and materials used in wood-bamboo composites. Further modifications are required to produce a stronger adhesive than the bamboo outer wall tissue in order to improve wet shear fiber failure rates.
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The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.
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