Changes in colour and mechanical properties of wood polypropylene composites on natural weathering


  • Jayashri Gunjal
  • Pankaj Aggarwal
  • Shakti Chauhan


Colour, flexural strength, mechanical properties, tensile strength, weathering, WPC


This comparative study focused on understanding the effect of coupling agent and particle size on weathering behaviour of wood polypropylene composite. Two coupling agents, namely maleic anhydride grafted polypropylene and m-TMI (m-Isopropenyl-a,a- dimethylbenzyl isocyanate) grafted polypropylene were used in preparation of the composites. The composites were exposed to outdoor conditions for one year and changes in surface colour and mechanical properties were measured after 2, 4, 8 and 12 months of natural weathering. During the initial four months of weathering considerable colour change was observed with increase in lightness.  Mechanical properties were unaffected largely for the initial four months and thereafter started declining.  Overall, tensile strength decreased by about 15 % and flexural strength decreased by about 8 % after one year of weathering. The flexural modulus also decreased by about 10 %. Wood particle size was found to affect the aesthetic and strength of the composites after natural weathering. Coupling agents had a positive impact on mechanical properties however their influence on weathering degradation was not noticeable.


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American Society for Testing Material. ASTM. 2014. D638-14: Standard Test Method for Tensile Properties of Plastics. ASTM International, West Conshohocken, PA, USA.

American Society for Testing Material. ASTM. 2015. D790-15: Standard test methods for flexural properties of unreinforced and reinforced plastics and electrical insulating materials. ASTM International, West Conshohocken, PA, USA.

Adhikary, K.B. 2008. Development of wood flour-recycled polymer composite panels as building materials. (Ph.D. thesis). University of Canterbury, Christchurch, New Zealand, pp. 229.

Andrady, A.L.; Hamid, S.H.; Hu, X.; Torikai, A. 1998. Effects of increased solar ultraviolet radiation on materials. J Photochem Photobiol B 46(1-3): 96-103.

Chauhan, S.; Aggarwal, P.; Karmarkar A. 2016. The effectiveness of m-TMI-grafted-PP as a coupling agent for wood polymer composites. J Compos Mater 50(25): 3515-3524.

Cherian, B.M.; Leao, A.L.; Chaves M.R.d.M.; Souza S.F. d.; Sain, M.; Narine, S.S. 2013. Environmental ageing studies of chemically modified micro and nanofibril phenol formaldehyde composites. Ind Crops Prod 49: 471–483.

Eshraghi, A.; Khademieslam, H; Ghasemi, I. 2016. Effect of weathering on physical and mechanical properties of hybrid nanocomposite based on polyethylene, wood flour and nanoclay. Maderas-Cienc Tecnol 18(4): 617-626.

Fabiyi, J.S.; McDonald, A.G. 2014. Degradation of polypropylene in naturally and artificially weathered plastic matrix composites. Maderas-Cienc Tecnol 16(3): 275 –290.

Fabiyi, J.S.; McDonald, A.G. 2010. Effect of wood species on property and weathering performance of wood plastic composites. Compos Part A Appl Sci 41(10): 1434-1440.

Fabiyi, J.S.; McDonald, A.G.; Wolcott, M.P.; Griffiths, P.R. 2008. Wood plastic composites weathering: Visual appearance and chemical changes. Polym Degrad Stab 93(8): 1405-1414.

Homkhiew, C.; Ratanawilai, T.; Thongruang, W. 2014. Effects of natural weathering on the properties of recycled polypropylene composites reinforced with rubberwood flour. Ind Crops Prod 56: 52–59.

Kale, A.; Raghu, N., Natu, H.P.; Aggarwal, P.; Chauhan, S. 2016. Effect of grafting yield and molecular weight of m-TMI-grafted-PP on the mechanical properties of wood fibre filled polypropylene composites. J App Polym Sci 133(46).

Klyosov, A.; 2007. Wood-Plastic Composites. Wiley & Sons, Inc. New Jersey, USA. 698 p.

Matuana, L.M.; Jin, S.; Stark, N.M. 2011. Ultraviolet weathering of HDPE/wood-flour composites coextruded with a clear HDPE cap layer. Polym Degrad Stab 96(1): 97-106.

Muasher, M.; Sain, M. 2006. The efficacy of photostabilizers on the colour change of wood filled plastic composites, Polym Degrad Stab 91(5): 1156-1165.

Poletto, M. 2017. Comparative study of wood flour photodegradation of two wood species submitted to artificial weathering. Maderas-Cienc Tecnol 19(2): 141 – 148.

Srinivas, K.; Pandey, K.K. 2012. Photodegradation of thermally modified wood. J Photochem Photobiol B. 117: 140-145.

Stark, N.M. 2007. Considerations in the weathering of wood-plastic composites. In Proceedings, 3rd wood fibre polymer composites international symposium. Bordeaux, France. March 26–27, 2007. 10 p.

Stark, N.M.; Matuana, L.M. 2006. Influence of photostabilizers on wood flour-HDPE composites exposed to xenon-arc radiation with and without water spray. Polym Degrad Stab 91 (12): 3048–3056.

Wolcott, M.P.; Englund, K. 1999. A technology review of wood–plastic composites. In Proceedings of the 33rd International Particleboard and Composite Materials Symposium. Pullman, WA, USA. 8 p.

Zhang, M..; Du, H.; Wang, W.H.; Wang, Q.W. 2010. Property changes of wood-fibre/HDPE composites colored by iron oxide pigments after accelerated UV weathering. J For Res 21(1): 59–62.




How to Cite

Gunjal, J., Aggarwal, P., & Chauhan, S. (2020). Changes in colour and mechanical properties of wood polypropylene composites on natural weathering. Maderas-Cienc Tecnol, 22(3), 325-334. Retrieved from