Recycling of cellulose-fiber-reinforced thermoplastic composites
Martina Prambauer, Oleksandra Voronych, Christoph Burgstaller
Transfercenter für Kunststofftechnik GmBH, Austria
Environmental concerns connected with new restrictive legal regulations have led to an increasing interest in the production of more environmentally friendly materials throughout numerous industrial areas, including the composite industry. For instance, by replacing synthetic reinforcement fibers by lignocellulosic plant fibers interesting composite materials with remarkable properties have been obtained. Plant fibers have high specific properties, are low in cost and density and are characterized by low energy input during their production. However, the natural variation in fiber quality is considered as one of their main drawbacks, which can be circumvented by applying processed plant fibers, such as pulp or paper fibers. Due to chemical or mechanical pulping processes, the fiber quality of the resulting cellulose pulps is more homogenous compared to natural plant fibers. This way, reinforcement fibers with high cellulose contents, suitable mechanical properties and constant quality are produced [1,2].
In this work, compounded and injection molded polypropylene composites, filled with paper snippets and MAPP as a coupling agent, were produced. After mechanical testing the specimens were re-processed in three cycles and the influence of material recycling on the composite’s properties were investigated by mechanical testing and SEM. Furthermore, cellulose fibers were extracted from the composites and a fiber length distribution, based on approximately 3000 fibers, was created for every recycling step. As a result, a significant reduction of the average fiber length due to processing and re-cycling was observed. However, the composite’s mechanical properties could be maintained at a high level, especially regarding the tensile modulus. Due to multiple shear-intensive processing steps, fiber defibrillation of the paper fiber bundles was observed causing an increase in contact area between cellulose fibers and polymer matrix. It is suggested that this led to an increase in mechanical properties, which acted as a counter effect to the property loss due to fiber degradation.
 Prambauer M, Paulik C, Burgstaller C (2016) Evaluation of the interfacial properties of polypropylene composite laminates, reinforced with paper sheets. Composites Part A 88: 59–66. DOI 10.1016/j.compositesa.2016.05.016
 Prambauer M, Paulik C, Burgstaller C (2018) Influence of paper content and matrix selection on the porosity, crystallinity and water uptake of thermoplastic paper composites. Journal of Polymers and the Environment, in press. DOI 10.1007/s10924-017-1098-y