Development of natural fiber reinforced composites with flame retardant fillers

Abstract

The global automotive industry is highly focused on application natural fibers with thermoplastic polymers due to its commercial applicability. Due to being environmentally friendly and having better advantages such as lightweight behavior, good strength to weight ratio and weather resistance, jute fiber has become a very suitable option to make composite material with thermoplastic materials such as polypropylene (PP). Application of jute fiber with PP matrix is growing day by day. In addition to that, flame retardant jute/PP composites have become a new set of trends of reliability. However, to achieve flame retardancy without compromising mechanical properties is a key concern to be noticed. In this thesis, flame-retardant jute/PP composites based on ATH/ZB and APP/ZB at a ratio of 80:20 were produced via combination of extrusion process and hot press method. Zinc borate (ZB) was used for creating a synergetic effect with aluminium tryhydride (ATH) and ammonium polyphosphate (APP). Before infusing flame retardant fillers to jute/PP composites, fiber loading levels were optimized with PP matrix at 20 wt.% of loading level based on long jute fiber (LJF) and short jute fiber (SJF) by the presence of 5 wt.% of maleic anhydrate-grafted polypropylene (MA-g-PP). The results indicated that length of short jute fiber was having a positive impact over mechanical properties (tensile strength and flexural strength). A maximum tensile strength value of 37.32±0.75 MPa and flexural strength value of 34.68±1.70 MPa have been achieved. Tensile modulus was reached to 1811±81 MPa and flexural modulus was reached to 1181±95 MPa. Further investigations were carried out with 20 wt.% SJF by increasing fiber loading up to 60 wt.% since the 20 wt.% SJF had been found to performed better than the 20 wt.% of LJF one in the initial mechanical property experiments. It was evident that increasing jute fiber content decreases tensile strength as well as strain (%) value. A clear noticeable decrease of tensile strength value (19.50±2.04 MPa) was found when 60 wt.% of SJF was infused within PP matrix. Until 40 wt.% of loading of short jute fiber flexural strength remains high (38.98±3.45 MPa) and consistent compared to others. But, when 60 wt.% loading of SJF was infused flexural strength value was decreased to minimum of 37.77±1.25 MPa was reached a tensile strength value of 19.50±2.04 MPa. Morphological analysis was carried out via scanning electronic microscope (SEM). Better adhesion was noticed for 30 wt.% loading of SJF which ensured optimum mechanical properties (tensile properties: strength-29.5±2.74 MPa, strain- 4.97±0.84 % and young modulus-1517±198 MPa; flexural properties: strength: 38.17±1.9 MPa, strain-7.18±1.17 % and flexural modulus- 1488±88 MPa) that was achieved. By keeping SJF loading level constant at 30 wt.%, as flame-retardant additives ATH/ZB and APP/ZB were incorporated at a loading level of 30 wt.% and 40 wt.% to achieve better flame-retardant properties without compromising mechanical properties. Char formation were greatly influenced via APP/ZB on jute/PP composites. To analyze flame-retardant behavior and thermal properties, UL-94 (Vertical burning and Horizontal burning), LOI, Cone calorimetry and TGA were carried out to investigate. An excellent flame retardancy was achieved at 40 wt.% loading of APP/ZB into jute/PP composites. V-0 classification level was achieved and 'no burning effect' was found which ensured self-extinguished (LOI- 28.8%) manner of flame-retardant jute/PP composite. A clear increment of LOI value was achieved up to 76.61% compared to unmodified jute/PP composite at a loading level of 30 wt.% of short jute fiber. Peak heat release rate (pHRR) was reached to 197.5 kW/m2 with total smoke production (TSP) value of 10.5 m2. Total heat release (THR) was 86.42 kW/m2. Effective hear of combustion value was 23.47 MJ/kg. Tensile strength and flexural strength increased by 15.86% and 81.21%, respectively. However, impact properties were negatively affected due to the high loading of APP/ZB. 35.68% decrease was noticed. Density was increased 18.75% compared to unmodified short jute fiber at a constant loading level of 30 wt.%. Inclusion of flame-retardant additives increased wear rate as well as value of co-efficient of friction (COF) significantly. A maximum increase of 195.75% was observed due to high pin temperature with self-extinguished APP/ZB based jute/PP composites. COF value was moderate compared to ATH/ZB at a loading level of 40 wt.%. Thermogravimetric analysis (TGA) results showed the maximum degradation rate temperature of the composite structures containing 40 wt.% of APP/ZB to be 481.62 oC, which was approximately 16 °C higher than that of the unmodified jute/PP composite at a short jute fiber loading of 30 wt.%. Fourier-transform infrared (FTIR) spectroscopy results was showed no significant differences within chemical structures of APP/ZB or ATH/ZB compared to unmodified jute/PP composites which signifies flame retardants were acted just as a filler to improve flame retardancy without any sorts of drastic changes into produced composites.