Improvement of mechanical and flame retardancy properties of biocomposites based on low density polyethylene and polylactic acid

Altun, Yasemin
The main objective of this study was to improve the mechanical and flame retardant properties of low density polyethylene (LDPE) and poly (lactic acid) (PLA) based biocomposites. Wood flour (WF) and jute fabric were used as the fillers. In the mechanical property improvement studies with LDPE, the effect of two compatibilizing agents MA (random terpolymer of ethylene, acrylic ester and maleic acid) and GMA (random terpolymer of ethylene, acrylic ester and glycidyl metacrylate) functionalized polymers at different concentration on the mechanical, morphological and water uptake properties of LDPE-WF composites were investigated. The effect of solution preimpregnation of WF with dilute compatibilizer solutions was also studied. . Fourier Transform Infrared Radiation (FTIR), Scanning Electron Microscopy (SEM), Tensile and Impact Tests and water-uptake determinations were conducted to investigate the mechanical, morphological, and water absorption properties of the WF-LDPE. According to the results, it was concluded that MA-composites were more effective than GMA based composites as a compatibilizer in LDPE–WF system. In addition, alkaline treatment and pre-impregnation were effective methods to increase the mechanical properties including tensile modulus, tensile and impact strength of LDPE-WF composites. In mechanical property improvement studies with PLA, the effect of alkaline treatment, WF ratio and pre-impregnation with dilute solution of polylactic acid (PLA) on the mechanical, morphological and water uptake properties of PLA-WF green-composites were studied. The similar characterization methods were used with LDPE-WF composites. According to results, the tensile strength of the composite increases as the amount of alkaline treated WF reaches 50 wt%. Furthermore, the preimpregnation of WF with dilute PLA solution further increases the tensile strength of the composites. In the second part of the study, flammability, thermal and combustion properties of LDPE-WF and PLA-jute fabric composites were improved. Limiting Oxygen Index (LOI), UL-94 test, Cone Calorimeter and Thermogravimetric Analysis (TGA) were used to investigate the flammability, thermal and combustion properties of the composites. Two different approaches were applied for producing flame retardant LDPE-WF composites. In the first approach, the flame retardant LDPE-WF was produced with the reduction of the flammability of both WF and LDPE. Accordingly, WF was treated with bis[tetrakis (hydroxymethyl) phosphonium] sulfate (THPS) or dicyandiamide-formaldehyde-phosphoric acid (DFP) flame retardants. Treated WF was used with ammonium polyphosphate (APP). As a result, the combined use of THPS or DFP treated WF with APP increased the fire performance of composites as 70% of decrease in peak heat release rate (pHRR) value with respect to the sample without flame retardant. In the second approach, the flammability of the matrix was reduced with the direct mixing of WF, matrix and the flame retardant material. Thus, LDPE, WF, red phosphorous (RP) or APP were directly mixed in the extruder to obtain flame retardant composites. RP was used for its synergistic effect for improving the flame retardant effect of APP. According to the results of the study, the combined use of APP and RP showed adjuvant effect. The maximum adjuvant effect was seen at ratio of 5:1 (APP: RP). In flame retardancy improvement studies with PLA, one approach was applied to produce flame retardant PLA-jute composites. PLA-jute composites were obtained with the reduction of the flammability of the jute fiber. To this end, jute fabric was treated with ammonium dihydrogenphosphate (ADP) and guanidine dihydrogen phosphate (GDP). The flammability and thermal properties of PLA based biocomposites were investigated. It was found that ADP treated jute fabric containing composite showed better flame retardancy and fire performance than GDP containing one.


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Citation Formats
Y. Altun, “Improvement of mechanical and flame retardancy properties of biocomposites based on low density polyethylene and polylactic acid,” Ph.D. - Doctoral Program, Middle East Technical University, 2015.