Evaluation of exploiting coffee wastes in production of PLA green composites

Nowadays, lot of attention is devoted both to the application of bio-based polymers as promising alternative to the currently used petro-based polymers, and to the recycling of waste materials coming from agriculture industry. However, a series of economic barriers hinder the application of bio-based polymers in large scale. The aim of this study was to evaluate the application of PLA composites containing up to a 30 %wt of wastes deriving from coffee production. The waste was coffee silverskin which is the main byproduct of coffee roasting process. The composites were formulated in three different proportions of waste including 10 %wt, 20 %wt, and 30 %wt of the composites. The mechanical properties, microstructure, and crystallinity of the composites, as well as thermal stability, water uptake, and contact angle have been evaluated. The results show that coffee silverskin did not compromise the thermal stability and degree of crystallinity of the composites, while it changed the mechanical properties. Specifically, tensile strength gradually decreased on addition of coffee silverskin, while the Young’s modulus slightly increased. The distribution of filler throughout the matrix was almost homogeneous without porosities in the composites. An increase in the value of water uptake was obtained, but the water absorption behavior was not modified. Furthermore, the values of contact angle were constant for all the composites. Due to the production conditions of this study, in order to obtain acceptable properties for the composites, the amount of waste should be limited up to 20 %wt. The simple and low cost operations performed on the waste for obtaining the filler, lead to a decrease in material price on account of PLA reduction. Moreover, using coffee waste as filler in production of green composites, in addition to adding value to agricultural waste, would results in minimizing the dependency on petro-based polymers.