Abstracts

Natural fibers nowadays play a very important role in the composites industry due to their several attractive characteristics especially energy saving potential which addresses the most vital industrial problem. Hence, this increasing demand of natural fiber thermoplastic composites in the market requires a technique to be established for handling the waste products out of these composites. The limitation of literature regarding the effect of recycling these for composites is the motivation for this work.This research focuses on recycling pre-consumer polypropylene compounds reinforced with sisal and hemp fibers up to five cycles. These two fibers are selected because they cover two main types of natural fibers: straight leaf fibers for sisal and branched bast fibers for hemp. Knowledge gained from these two types serves as a basis which could be implemented in future on other fibers from the same type.Natural fibers being natural products unlike synthetic fibers, offer unusual scatter of values, which in turn leads to the difficulty of assessing the effect of several reprocessing cycles on the compound. To be able to set a good foundation for this research, a thorough investigation on sisal and hemp fibers in both dry and compounded (with polypropylene) states is performed in the first section of this research followed by recycling of sisal and hemp compounds. A thorough investigation for determining the evolution of fiber shape and morphology is conducted on extracted fibers at selected cycles using dynamic image analysis in addition to FESEM and digital microscopy. Followed by rheological, flowability and thermal tests, the effect of number of cycles on the resulting properties could be analyzed based on the understanding of fibers morphology. Finally, mechanical tests are performed to assess the change in the compounds properties after recycling regarding the gained knowledge from the previous analysis.Understanding the difference in nature and consequently the difference in behavior between sisal and hemp fibers in the polypropylene melt gives an insight into comprehending the rheological and mechanical behavior of the compounds under study. Sisal with its straight and stiff fibers is less likely to agglomerate and build fiber clusters and is homogeneously distributed in the PP matrix. On the contrary, hemp fibers which are thin, branched and flexible tend to tangle up and build agglomerations of fiber clusters which hinder the homogenous distribution of the fibers in the matrix PP. This behavior affects the development of the viscosity along recycling cycles where sisal compound proves higher viscosity than hemp compound in the first cycles. Afterwards, due to recycling, hemp agglomerations disentangle and hemp fibers are shortened and distributed homogenously in the PP matrix causing increase in the overall compound viscosity. Flowability values show a three-stage behavior where compounds start at relatively low values (long sisal fibers / agglomerated hemp fibers). After the first and secondAdvisors/Committee Members: Ziegmann, Gerhardf.