Comparison of Two Wood Plastic Composite Extruders Using Bootstrap Confidence Intervals on Measurements of Sample Failure Data

Wood plastic composite (WPC) boards are an emerging engineered wood composite that is a substitute for solid wood and other wood composite materials used for exterior applications, primarily decking. We are interested in understanding the strength of these boards and estimating the lower percentiles of failure under perpendicular pressure. The strength of WPC is determined by the perpendicular pressure required to permanently deform a board (modulus of elasticity, MOE) and the perpendicular pressure required to rupture the board (modulus of rupture, MOR). Two WPC production-size extrusion lines at the same facility are compared in this article by comparing the distributions of pressure to failure for samples of WPC extruded from each line. Parametric bootstrapping is used to calculate confidence intervals of the 1st, 5th, and 10th percentiles of the MOE and the MOR from each line. Furthermore, both parametric and nonparametric bootstrapping are performed to estimate confidence intervals on the differences between the two lines for the 1st, 5th, and 10th percentiles of the MOE and the MOR. A statistical difference between the strength of the WPC extruded from the two lines is found in the MOR.