To suppose an industrial development of softened or densified composites, any possible further processing has to be evaluated.
Two polyurethane coatings systems (primer + top-coat), aqueous and solvent based, have been applied on densified composite. Visual inspection is satisfaying. Cross-cut (Figure 13) and impact normalized tests show comparable results as those obtained with the same coating systems applied on wood.
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Fig. 13. Cross-cut testing carried out on aqueous based coating applied on densified composite |
Tools wearing during machining has to be considered as well. Sanding paper is already been recognized as easily spotted when used to sand densified composite samples. Attention must be paid to blades, since surface acidity of densified samples is around pH 3 (wood surface acidity being around pH 6 to 7).
3. Conclusion
Lactic acid oligomers have been used as reinforcement into the lignocellulosic matrix. Without any polymerization catalyst, the densified composite obtained is stable, biologically resistant and mechanically competitive: high density and good hardness results make it suitable for flooring application for instance.
When a polymerization catalyst is added to the oligomers, wood components are damaged. The softened composite obtained can however be hardened again since an extended heating leads to a stable and biologically resistance material. The middle lamella degradation provokes mechanical properties decrease which suggests applications as decorative moulded objects or covering panels rather indoor that outdoor, for instance.
Manufacturing conditions can obviously be optimized to lead to a better composite material: temperature, duration, chemical catalysts, etc.
Another field of interest would be either to reinforce wood structure with other bio-polymer molecules, or to use lactic acid oligomers mixture to reinforce other natural matrices as bamboo for instance.
4. References
Bledzki, A. K.; Gassa, J. (1999). Composites reinforced will cellulose based fibres Progress in polymer science, 24, 221-274
Ganster, J.; Fink, H.-P. (2006). Novel cellulose fibre reinforced thermoplastic materials Cellulose, 13, 271-280
Gatenholm, P.; Kubat, J.; Mathiasson, A. (1992). Biodegradable natural composites. I.
Processing and properties Journal of applied science, 45, 9, 1667-1677 George, J.; Sreekala, M. S.; Thomas, S. (2001). A review on interface modification and characterization of natural fiber reinforced plastic composites Polymer engineering and science, 24, 41, 1471-1485
Ibach, R. E.; Rowell, R. M. (2001). Wood preservation based on in situ polymerization of bioactive monomers. Holzforschung, 55, 358-372 Noel, M.; Fredon, E.; Mougel, E.; Masson, D.; Masson, E.; Delmotte, L. (2009) Lactic acid/wood-based composite material. Part 1: Synthesis and characterization Bioresource Technology, 100, 4711-4716
Noel, M.; Mougel, E.; Fredon, E. ; Masson, D. ; Masson, E. (2009) Lactic acid/wood-based composite material. Part 2: Physical and mechanical performance Bioresource Technology, 100, 4717-4722
Rowell, R. M. (2005). Chemical modification of wood, In: Handbook of wood chemistry and wood composites, Vol. 14, Ed. Taylor and Francis, 381-420 Zhang, Y.; Zhang, S. Y.; Yang, D. Q. ; Wan, H. (2006). Dimensional stability of wood-polymer composites. Journal of applied polymer science, 102, 5085-5094
