Preparation And Research On Phosphorus-containing Flame Retardant Properties Of The LDPE-base Cable For Nuclear

Phenoxycyclophosphazene(HPCTP) and poly[bis(phenoxyphosphazene)](PBPP)were chose as flame retardant and anti-radiation additives for low-densitypolyethylene (LDPE) composites, due to synergistic effect of nitrogen and phosphoruson flame retardant. The radiation effects of LDPE, radiation effects and thermalstability of HPCTP were investigated. Processing properties, mechanical properties,flame retardant and anti-radiation properties of LDPE composite materials were alsoinvestigated. The main content of this thesis is as follows:(1) The effect of radiation on LDPE material was studied and compared with low andhigh dose rate in air atmosphere. The free radical, carbonyl index, gel content,mechanical properties such as tensile strength and yield strength were investigated atdifferent absorbed dose. The gel content measurements showed that the gel contentincreased with absorbed dose increase, the sample with different dose rate andthickness had the same trend, high dose rate induced much more cross-linking thannormal dose rate. The mechanical test showed that electron beam irradiation at lowdose rate induce much more damage on mechanical properties of LDPE than that athigh dose rate; the thinner the thickness, the more serious the injury. The calculationof carbonyl index showed that the oxidation level of irradiation at low dose rate isgreater than that at the high dose rate especially on surface area and the sample withthinner thickness had much more serious oxidation. This is because the diffusion ofoxygen is the mainly factor to affect the oxidation, becomes thinner and moreconducive to oxygen. The electron spin-resonance spectroscopy (ESR) measurementproved that the lower dose rate of irradiation induced much more radicals than that athigh dose rate. Differential scanning calorimetry (DSC) measurements showed thatthe dose rate had great effects on crystal structure of LDPE, at high dose rate, thecrystallinity of LDPE increased at small dose but decrease at high absorbed dose,while at low dose rate, the crystallinity decreased with dose increase.(2) The radiation effects of HPCTP and thermal stability were systematically invested.HPCTP is resistant to the effects of the electron beam radiation due to its rich electronic structure. Research on the radiation stability using high performance liquidchromatography (HPLC), when the absorbed dose is1000kGy, the loss rate is only28%. And study on the generation using HPLC-MS and infer structure of generation;the thermal stability of HPCTP was invested by Thermal Gravimetric Analyzer-Infrared Radiation (TG-IR), the results showed that the decomposition temperature ofHPCTP is383℃, the main product from the thermal decomposition are benzene andits derivatives.(3) Preparation of flame retardant composites by blending HPCTP, PBPP with LDPEand magnesium hydroxide (MH) respectively. The results of melt flow rate andrheological properties proved that HPCTP, PBPP can promote the molecular motionof LDPE, and improve the interfacial interaction between LDPE and MH. Thus, theprocessing performance of the composite material was improved. The compositionand structure of composite material were characterized by IR, scanning electronmicroscope (SEM) and X-ray diffraction (XRD). The results of IR and XRD showedthat the addition of PBPP did not change the structure and crystallization of LDPEand MH. The MH particles were uniformly dispersed in the LDPE matrix observed bySEM, It was proved by Energy Dispersive X-Ray Spectroscopy (EDX) that HPCTP,PBPP coated on the surface of MH particles. The thermal properties and flameretardant of the composite material were characterized by TGA and LOI. The resultsof TGA showed that HPCTP and PBPP decreased the initial decompositiontemperatures of the composites, and promote the carbonation of LDPE, and the resultof limiting oxygen index (LOI) showed that the flame retardant improved with theincreasing of HPCTP or PBPP content in the composite. The experimental results ofirradiation showed that the elongation of the composites added with HPCTP or PBPPwere higher than that without ones. And the composites after radiation werecharacterized by HPLC-MS and TGA. It proved that HPCTP or PBPP is the sacrificethemselves to protect polymer.(4) The preparation of flame retardant composites using EVA addingLDPE-MH-HPCTP and LDPE-MH-PBPP blend systems, as a compatibilizer,respectively. The results of melt flow rate test showed that HPCTP or PBPP could improve the processing performance of the composite materials.The composition andstructures of composites were characterized by FTIR, SEM and XRD. The results ofFTIR and XRD showed that the addition of PBPP did not change the structure andcrystallization of LDPE and MH. The MH particles were uniformly dispersed in theLDPE matrix observed by SEM, and the MH and EVA-LDPE matrix interfaces moreclosely integrated. The thermal properties and flame retardant of the composite werecharacterized by TGA and LOI. The results of TGA showed that HPCTP and PBPPdecreased the initial decomposition temperatures of the composites, and promote thecarbonation of LDPE, and the result of LOI showed that the flame retardant improvedwith the increasing of HPCTP or PBPP content in the composite. The experimentalresults of irradiation showed that the elongation of the composites with HPCTP orPBPP is the same with that without ones. It indicates that the HPCTP or PBPP playedthe role of lubricants, and did not play the role of anti-radiation in the radiation of thecomposites.(5) The precipitation of HPCTP in cross-linked LDPE material under aging wasinvested. Mechanical properties, free volume, surface morphology and LOI of HPCTPcontaining cross-linked polymers were tested in the different time at150℃and180℃. The results show that, mechanical properties of composite materialsunchanged with the increasing of aging time at150℃, however, decreased with theincreasing of aging time at180℃. The results of dynamic thermomechanical analysis(DMA) tests showed that, materials changed into much hard after thermal aging. Thetests of free volume showed that molecular chain segment are rearranged and stretchduring annealing of composites at high temperature in a short time, which leading tosmaller free volume. Polymer chain segment start to break with the increasing ofaging time, which resulting in larger free volume. The results of IR and SEM testsshowed that HPCTP precipitated seriously with the increasing of aging time.