Macro and micromechanics analysis of short fiber composites stiffness: The case of old newspaper fibers–polypropylene composites

Stiffness is one of the most relevant characteristics of composite materials. Natural wood fibers have demonstrated their ability to increase the Young’s moduli of composite materials, and old newspapers are a potential source of reinforcing fibers for composite materials. There are some micromechanic models to predict the Young’s modulus of composite materials, and one of the input data is the intrinsic modulus of their fibers. This intrinsic modulus is a value which is difficult or impossible to measure in the case of wood fibers, due to their measures. This paper evaluates the stiffening abilities of old newspaper fibers and the possibility to back calculate the value of the intrinsic Young’s modulus by means of micromechanic models. Different percentages of old newspaper fibers were compounded with polypropylene (PP). Micromechanics of the fibers were obtained using Hirsch model, Cox–Krenchel’s model, Tsai–Pagano model and Halpin–Tsai equations. The most important results were the average intrinsic Young’s modulus of the fibers, the mean orientation angle and the mean modulus efficiency factor.