How do plywood pallets maintain dimensional stability and avoid delamination or warping in high-temperature and high-humidity environments?
Publish Time: 2026-02-18
In modern warehousing, logistics, and international trade, plywood pallets have become a mainstream alternative to traditional solid wood pallets due to their high strength, lightweight, fumigation-free operation, and environmental recyclability. However, in high-temperature and high-humidity environments such as tropical sea transport, cold storage, and rainy season storage, wood materials are highly susceptible to moisture absorption and expansion, and adhesive failure, leading to pallet deformation, delamination, and even structural collapse. The key to plywood pallets maintaining excellent dimensional stability under such harsh conditions lies in the systematic synergy of their raw material selection, adhesive system, hot-pressing process, and structural design.1. Multi-layered cross-laminated structure: The natural mechanical basis for inhibiting deformationPlywood pallets are made by assembling an odd number of veneers perpendicular to each other along the grain direction. This "cross-laminated" structure is the core of its anti-deformation properties. When the ambient humidity changes, the wood will expand or contract slightly along the fiber direction, but because the grain of adjacent layers is orthogonal, the deformation in each direction is mutually restrained, and the net deformation of the overall board in the length and width directions is largely offset. Compared to solid wood pallets, which are prone to warping and cracking due to uneven moisture content, plywood pallets, thanks to their inherent balancing mechanism, significantly improve planar stability, effectively preventing cargo tilting or stacking instability caused by twisting during use.2. High-Performance Waterproof Adhesives: A Key Barrier Against Humid Heat and MoistureThe durability of plywood pallets in high-temperature and high-humidity environments largely depends on the water resistance of the adhesives used. High-quality pallets generally use WBP-grade adhesives, such as phenolic resin or melamine-modified urea-formaldehyde resin. These adhesives, after high-temperature curing, form a highly cross-linked three-dimensional network structure with extremely strong hydrolysis and heat resistance. Even after long-term exposure in environments above 60°C and relative humidity above 90%, the adhesive layer maintains its bonding strength, preventing delamination between veneers.3. High-Temperature and High-Pressure Molding Process: Eliminating Internal Stress and Improving DensityDuring the manufacturing process, plywood pallets undergo hot pressing at 130–150°C and 8–15 kg/cm² pressure. This process not only promotes full cross-linking and curing of the adhesive but also effectively removes moisture and air from the wood, resulting in a uniform board density and a compact structure. More importantly, the slow cooling after hot pressing helps release residual stress within the board, preventing warping caused by uneven stress during subsequent use. Simultaneously, the high-temperature treatment kills insect eggs and microorganisms, further enhancing the pallet's biological stability in humid and hot environments.4. Edge Banding and Surface Treatment: Building an Additional Protective LayerAlthough plywood itself has some moisture resistance, its ends and edges remain the primary channels for moisture intrusion. High-end plywood pallets often undergo edge banding treatments—such as applying waterproof wax, spraying acrylic sealant, or applying PVC edge banding strips—to form a continuous sealed barrier, blocking capillary absorption pathways. In addition, some products apply a hydrophobic coating to the panel surface to further reduce surface moisture absorption, keeping the pallet dry and rigid when stored on damp ground or in the open.In summary, the plywood pallet, through its multi-layered orthogonal structure, high-performance waterproof adhesive, precision hot-pressing process, and edge protection measures, constructs multiple lines of defense in high-temperature and high-humidity environments, effectively maintaining dimensional stability and preventing delamination and warping. It is not only a logistics carrier but also a model of the integration of materials science and engineering practice, providing solid support for the efficient and secure operation of the global supply chain in complex environments.
