(409c) Effect of Fiber-Matrix Combatibilization Techniques On the Creep Behavior of Phbv/Wood Flour Biobased Composites

Fully biobased composites of bacterially synthesized poly(β-hydroxybutyrate)-co-(β-hydroxyvalerate) (PHBV) with oak wood flour filler have the potential to have a self-feeding carbon cycle: their constituents can fully biodegrade in anaerobic conditions resulting in carbon feedstock for the constituents. These composites have been shown to have similar material properties to certain engineered woods and glass fiber filled polymers. However, the creep properties of these composites have not been fully assessed; this assessment is necessary to be able to predict time-dependent behavior in load bearing applications.

While inclusion of wood flour in polymer composites has been popular in research due to the low cost of the fiber and the potentially environmentally favorable characteristics it provides, there are some disadvantages associated with natural fiber reinforcement in polymers.  One disadvantage is the incompatibility of hydrophilic natural fibers and hydrophobic polymer matrices, which can lead to poor dispersion of fibers and low mechanical properties [1]. Use of compatablizing agents to improve the interface between matrix and natural fibers has shown to reduce creep behavior in wood flour filled composites through improved wettability and dispersion [2].

In this research, creep behavior was assessed for PHBV/wood flour composites with varying fiber volume fraction (0%, 20%, & 40%) and compatabilizing agents, namely maleic anhydride grafting of the polymer and silane treatment of the fibers were considered. Composites were subjected to three sustained flexural loading scenarios at approximately 9%, 18%, and 27% of their ultimate flexural strength. After the composites were analyzed for time-dependent deflection accrued during sustained loading, they were allowed to recover. Quasi-static flexural tests were then performed on the specimens to determine loss of mechanical properties due to creep. In addition to these analyses, applicability of Burger’s four-element phenomenological model and Findley’s power law model were assessed for their ability to capture composite creep behavior.

It was found that both fiber volume fraction and compatibilizing agents influence creep behavior of this class of composites. Most typically, increased fiber volume fraction and use of compatibilizing agents reduced creep deformation over time with some exceptions. For most cases examined, there was no statistically significant change in quasi-static mechanical properties as a result of creep loading. Of the two models examined, the Findley model captured the creep behavior of the composites better for the behavior and time considered; however, Findley’s model, unlike Burger’s model, cannot be used to predict other material properties [2].

References

[1] Srubar, W.V. III, Pilla, S., Wright, Z.C., Ryan, C.A., Greene, J.P., Frank, C.W., Billington, S.L. (2012) Mechanisms and impact of fiber-matrix compatibilization techniques on the material characterization of PHBV/oak wood flour engineered biobased composites. Composites Science and Technology (72)

[2] Nunez, A.J., Marcovich, N.E. and Aranguren, M.I. (2004). Analysis of creep behavior of polypropylene-woodflour composites. Polymer Engineering and Science (44) 8