Study On Preparation Of Glass Fiber Reinforced PA66 With High Comparative Tracking Index And Non-halogen Flame-Retardancy

In recent years,with the rapid development of China's industry,the demand for engineering plastics is growing.In the harsh environment of high temperature and high current,it requires the high tracking resistance and flame retardancy to prevent materials from tracking and burning.Nylon 66(PA66)has good mechanical properties,heat resistance,processability and electrically insulated properties,so it is widely used in automotive industry,mechanical equipment and electronic and electrical fields.However,PA66 and glass fiber reinforced PA66 composites have the poor flame retardancy,which limits their usage and needs to be modified.Although the traditional halogen flame retardant is commonly used in the industry,it will sharply reduce the comparative tracking index(CTI)of PA66,and release the toxic gases during the combustion process of the material.As an eco-friendly flame retardant,hypophosphonate is able to improve the flame retardancy and CTI of the material at the same time,but the higher price limits its application.Therefore,it is urgent to develop a green flame retardant with the lower cost to simultaneously improve the flame retardancy and tracking resistance of PA66.Melamine polyphosphate(MPP)is an environmental-friendly and low-cost intumescent flame retardant,which is often used in the flame retarded PA66.However,it has a negative effect on the tracking resistance of PA66 and is not able to be used alone.Zinc borate(ZB)is also an environmental-friendly halogen-free flame retardant.It releases the crystal water above 300?,and generates the film-like glass B₂O₃,the former absorbs a large amount of heat,and the latter is beneficial for the flame retardancy and smoke suppression,preventing melt dropping and improving the resistance to tracking of materials.Talc is an economical inorganic reinforcing filler,and also releases the crystal water at high temperature,which absorbs heat.Moreover,the regular talc sheet can generally reinforce the carbon layer,improving the flame retardancy and tracking resistance of materials.In this paper,the flame retardancy and tracking resistance of glass fiber reinforced PA66 composite were investigated by the combination of MPP with ZB and Talc,respectively.The aim of this paper is to prepare a new flame retarded system with low cost,environmental-friendly,which simultaneously improves the flame retardancy and tracking resistance of PA66.In the end,in order to expand the application of PA66 in the electronic and electrical fields,Si-DPF,a home-made flow modifier,was used in flame retarded and glass fiber reinforced PA66 composites for the further improvement in CTI,flame retardancy,mechanical properties and processing properties.(1)The research dealt with effects of MPP,ZB,talc or GF used individually on flame retardancy,tracking resistance,processability,heat resistance and mechanical properties of PA66.The results showed that the flame retardancy of PA66 was not improved by ZB or Talc alone,both ZB/PA66 and talc/PA66 did not reach the level of UL-94 V-2@3.2 mm.MPP alone improved the flame retardancy of PA66,but the flame retardant efficiency is low.20wt%or over MPP endowed the MPP/PA66 composite with UL-94 V-0@3.2 mm level.ZB,talc or GF used alone,the CTI of PA66 composites retained as 600 V,while MPP reduced the tracking resistance of MPP/PA66 for the carbonization catalyzed by MPP.The CTI of MPP/PA66 composite was decreased from 600 V to 300 V at the loading of 10 wt%.When the MPP content was increased to 30 wt%,the flame retardancy and CTI reached a high level at the same time,indicating that both is not absolutely irreconcilable in a sense.The flame retardant at the proper loading delayed the occurrence of combustion in the process of tracking,thus improving the CTI of the material,while the flame retardant at excessive or insufficient loading promoted the formation of carbon tracks,which reduced the CTI of the composites.(2)The flame retarded and glass fiber reinforced PA66 composites were prepared in extrusion.It was investigated the relationship between the flame retardancy,tracking resistance,mechanical property and heat resistance of 30 wt%glass fiber reinforced PA66composites and the combined flame retardants of MPP and ZB,or MPP and talc.When the loadings of GF and MPP were 30 wt%and 15 wt%,respectively,the CTI of GF/MPP/PA66was only 250 V,while another 5 wt%inorganic filler was combined,the CTI of GF/MPP/Talc/PA66 was increased to 300 V,and that of GF/MPP/ZB/PA66 went up to 600 V.Meanwhile,the mechanical properties and flame retardancy of the three composites reached the better level,which passed the test of UL-94 V-1@3.2 mm.In the test of CTI,the surface of GF/15-MPP/5-ZB/PA66 was not carbonized by the initial dry band discharge,so the initial leakage current waveform is like that appeared in the test of the ceramic insulation material.With the progress of test,the carbon track gradually developed,and the current duration prolonged.The leakage current waveform for GF/15-MPP/PA66 was similar to that for GF/15-MPP/5-Talc/PA66,but after combustion,the leakage current of GF/15-MPP/PA66 was increased faster.The results from Raman spectra and scanning electron microscopes showed that there was less graphitized carbon layer on the surface of GF/15-MPP/5-ZB/PA66composite.The results from thermogravimetry infrared spectroscopy showed that the degradation of GF/15-MPP/PA66 and GF/15-MPP/5-Talc/PA66 was severer than that of GF/15-MPP/5-ZB/PA66.(3)The flame retarded and glass fiber reinforced PA66 composites were further modified by a dispersant(Si-DPF)made in the laboratory.The results showed that the addition of 3wt%Si-DPF was able to improve the flame retardancy and CTI of the composites,the crystallinity of PA66 in the composites was improved,and the melt flow,density distribution,mechanical properties of the composite were also improved.After adding 3 wt%Si-DPF,the crystallinity of PA66 in GF/15-MPP/5-ZB/PA66 composite was increased from 21.2%to23.9%,the melt equilibrium torque was decreased to 1.4 N·m,which decline was 33.3%,and the tensile strength and bending strength were increased by 9.1%and 8.4%,respectively,which reached 139.0 MPa and 215.0 MPa,respectively,and passed UL-94 V-0@3.2 mm test.The crystallinity of PA66 in GF/30-MPP/5-Talc/PA66 composite was increased from 17.9%to 24.2%,the melt equilibrium torque was decreased by 29.1%,the tensile strength and bending strength reached 99.2MPa,166.5MPa,respectively,the rises were 9.4%and 41.7%,respectively,and the fracture of the far gate was also improved.