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Viscoelastic properties of maleated polypropylene(MAPP)-modified wood flour/polypropylene composites(WPC)were investigated by both a compression stress relaxation method and dynamic mechanical analyses(DMA).Three wood to polymer ratios (40:60,60:40,and 80:20)and five MAPP loading levels(0,1,2,4 and 8%)were used to study their effects on the viscoelastic properties of MAPP-WPC.The results show that: 1)higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC.The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios(60:40 and 80:20),but almost no effect at the 40:60 wood to polymer ratio.The optimal MAPP loading level for the wood to polymer ratio of 60:40 appears at 1%; 2)the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40:60 and 60:40,while for the 80:20 wood to polymer ratio,a higher storage modulus is observed at higher MAPP loading levels,which is quite consistent with the stress relaxation results.The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios.Excessive MAPP loading would have resulted in adverse effects.