Investigation of mechanical, thermal and flame retardant properties of glass fiber reinforced PBT and PBT/PET blends

Abstract

Engineering plastics are used more and more areas in a wide spread manner. Especially, need of special performance characteristics, engineering plastics are come to mind. These special characteristics can be defined as high mechanical properties, high abrasion resistance, high electrical and thermal resistance, improved fire retardant performance. Plastics are used in different significant areas such as aeronautics and space, construction, defense industry, automotive, electrical and electronical industry etc. Improvement of mechanical, thermal and fire retardant performance of these engineering plastics, become more of an issue. In order to reach these desirable performance characteristics, manufacturers use reinforcement agents and additives. Glass fibers are commonly used to support polymeric structure with the purpose of obtain stiffness, strength and flexibility. Glass fiber reinforced engineering plastics have also varied fire behavior depend on resins which are used. Previous studies show that scientists had preferred halogenated flame retardants because of their outstanding fire retardant performance in case of fire. By the reason of legislative restrictions (such as REACH), environmental and health considerations, halogen free flame retardant additives have become more and more important. Also, high temperature stable mineral fillers are used to improve thermal properties. The combination of halogen free flame retardants and mineral fillers, give a new impulse to fire retardant performance of engineering plastics. This combination also reduces the cost of high fire retardant performance plastics. Poly(butylene terephthalate) (PBT) is preferred among engineering plastics with its high dimensional stability, low moisture absorption, productivity and fast cycle time characteristics. However, glass fiber reinforced PBT grades have preferred due to modified mechanical properties. Glass fiber reinforced PBT/PET blends have desirable properties such as glossy surface appearance, high rigidity, high temperature and strength properties. Additionally, the most important characteristic of glass fiber reinforced PBT/PET blends is good cost-performance ratio. After the restriction of halogenated based flame retardant, halogen free high performance phosphorus based flame retardant additives are preferred to use in engineering plastics. In this study, samples were prepared by using co-rotating twin screw extruder and they were shaped by injection moulding machine. A halogen free phosphorus based flame retardant additive which is called aluminium diethyl phosphinate is used as main flame retardant. This halogen free phosphorus based flame retardant is also called DEPAL and especially identified as AlPi – Et in scientific researches. Two aluminium based mineral filler are used as a co-flame retardant which has the same chemical structure but they have different average particle size and specific surface area. In first stage of experiment, Actilox B60, which its particle size is 1.2 m, aluminium based mineral filler is used as co-flame retardant. In second stage of experiment, Actilox B30, which its particle size is 2.3 m, aluminium based mineral filler is used as co-flame retardant. This aluminium based mineral flame retardants are boehmite originated and its chemical formula is AlO(OH). All samples contain totally 20% flame retardant additives except control sample. The samples were extruded with different matrices which are neat PBT, glass fiber (GF) reinforced PBT and GF reinforced PBT/PET blend. In order to determine optimum combination of main flame retardant/co-flame retardant, five different ratios are selected. In first stage of the experiment, Actilox B60 is used and these main flame retardant/co-flame retardant ratios are aligned as 20% DEPAL/0% Actilox B60; 15% DEPAL/5% Actilox B60; 10% DEPAL/10% Actilox B60; 5% DEPAL/15% Actilox B60 and 0% DEPAL/20% Actilox B60. In second stage of experiments, samples were prepared with Actilox B30 as co-flame retardant and the main flame retardant/co-flame retardant ratios are 20% DEPAL/0% Actilox B30; 15% DEPAL/5% Actilox B30; 10% DEPAL/10% Actilox B30; 5% DEPAL/15% Actilox B30 and 0% DEPAL/20% Actilox B30. Structural properties of samples were evaluated by measurements of density and melt flow index (MFI). In order to obtain mechanical properties of samples; stress at break, tensile modulus, strain at break and Izod impact (+23 °C and -30 °C) values are calculated. Thermal properties of samples were investigated by heat distortion temperature (HDT), thermal gravimetric analysis (TGA) and differential scanning calorimeter (DSC) analysis. Flame retardant performance of the samples were obtained by UL 94, glow wire ignition temperature and glow wire flammability index tests. In consequence of all experiments; Sample 27, which is contained 5% DEPAL/15% Actilox B30 in 20% GF reinforced PET/PBT blend matrix, is given the best mechanical, thermal and fire retardant performance results.