Sensitivity to moisture is an inherent problem in paper, which limits its application in components. Whenever the temperature and relative humidity of the surrounding environment change, the moisture content of the paper changes rapidly to achieve a balance in the new state. Excellent plasticizers, especially with any change in moisture content, all physical properties of the paper will change. When a hydrophobic resin (such as phenolic aldehyde) is sandwiched in the fiber network, the rapid exchange of moisture is greatly suppressed, but there is no loss. It only takes a long time to get a balance. However, the qualitative effect of moisture changes in the laminate is still evident. The higher the moisture content, the more plasticized the laminate and the lower its tensile modulus and stiffness.
Changes in the moisture content of plastic laminates can also cause changes in their physical dimensions. The change is inconsistent in all directions, and the change in the thickness direction is the largest. The most stable direction of the laminate is equivalent to the longitudinal dimension of the paper machine. Typical variations for commercial decorative laminates are: 0.1 ft to 0.3% in the longitudinal direction, 0.7% to 1.0% in the transverse direction, and 5% to 10% in the thickness direction. This value is for the humidity to change from 2% to 98%. The actual test  used two samples: one humidity change was from 55% to 2%, and the other humidity change was from 55% to 98%. It takes a day to get a true balance of 55% to 2% humidity change, and a 55% to 98% humidity change takes 7 days. The inconsistent swellability observed in plastic laminates is directly related to the inconsistencies (i.e., anisotropy) of the cellulose fibers. The hard resin itself is isotropic. Due to the microscopic and submicroscopic structure of the fiber, it is difficult to change the size in the axial direction when the moisture content changes, but rapidly expands and contracts in the radial direction. There is no free space in the plastic laminate
Inter- or void, so any change in fiber size translates directly into a change in laminate size.
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