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Autori: Alex Dragomirescu, Jim Nash
Editorial: 9th International Conference on Wood & Biofiber Plastic Composites, Madison, Wisconsin, USA, 2007.
The tendency of wood-plastic composites (WPC) to absorb moisture is very important in the processing and also in mechanical properties, appearance, dimensions. Swelling of natural fibres can lead to cracking of the material, degradation and poor mechanical properties. The potential effect of water absorption on WPC composites is discussed based on known results from a long experience in testing Enviroshake® engineered roofing material. This presentation contains data obtained in laboratory as well as in the field.
The effect upon composites properties of change in moisture content due to water absorption depends on the type of exposure (by immersion in water or by exposure to high humidity), shape of the part, and inherent properties of the material. With non-homogeneous materials, such as Enviroshake®, the rate of water absorption may be widely different through each edge and surface. An in-house method based on ASTM D570 was employed to study the effects of exposure to water or humid conditions for WPC material.
To verify the acceptability of the roofing product characteristics and process capability, some daily QC test results have also been analyzed. Water absorption (24 hours) average was 1.12% while the maximum admissible is 3%; values were between 0.50 and 2.17%. All data (approximately 5500) have been summarized graphically. None of the samples showed any signs of cracking, spalling, or other forms of deterioration. However, the frequency and amplitude are not uniform, the curve having a random aspect, which makes difficult to do estimations or find an empirical formula.
Cuvinte cheie: wood plastic composites, polymers, plastics, water absorption