Environmentally friendly thermoplastic composite from natural banana fibers and recycled PET

Today's society faces the accumulations of considerable amounts of plastic waste. This waste can be managed in several ways, and one of them is recycling. In this work, the design of a composite is made from recycled polyethylene terephthalate (PET) and natural banana fibers (BF) with an environmentally friendly mindset. Unfortunately the melting temperature of PET is around 250-260°C and the thermal stability of a banana fiber is around 200°C. PET is therefore chemically modified to lower its melting temperature. This modification consists of a depolymerisation by glycolysis with 1,3-propanediol (1,3-PD). Followed by a repolymerisation, with a chain extender made of 1,3-PD and succinic anhydride (SA), which contributes to the reduction of the melting temperature while increasing the molar mass. 1,3-PD and SA can be produced in a bio-sourced way. The next step is solid state polymerization (SSP) to further increase the molar mass. Finally the influence of tetraglycidyl 4,4 diaminodiphenyl methane epox (TGDDM) as chain extender is studied in different proportions and for different reaction times. However, a higher concentration of TGDDM does not further increase the molar mass as expected. It may rather react with small chains to make a branching structure or react with water molecules and gender degradation by transesterification. Before addition of BF in the matrix, acid and alakaline treatments on BF were studied. Alkaline treatment of the fiber increases the thermal stability by 20°C compared to untreated fiber and allows a good cohesion with the matrix. Acid treated fibers have residues on the surface that must be removed by cleaning. Otherwise, these residues mix and react with the matrix during extrusion and make the matrix brittle. This leads to low mechanical properties for the composite. Influence of BF loading content in the matrix corresponding to 5, 10 and 20$\%$ was done for alkaline treated BF. The amount of fiber improves the mechanical properties but renders the material brittle, whereas the matrix has a strain at break exceeding 110%. The highest Young’s modulus is observed for 20wt.$\%$ BF and has a value of 4.75 GPa Influence of annealing temperatures has been done to show the behavior of the composite and the increase of crystallinity that it generates. The techniques used for the charachterisation are the Ubbelohde viscometer to determine the molar weights, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for thermal charachterization, tensile tests for the mechanical analysis, dynamic mechanical analysis (DMA) for thermomechanical charachterization, and at last, scanning electron microscopy (SEM) for morphologic characterization.