Preparation And Properties Of Polyphenylene Oxide/Elastomer Composites

Most of the polymer materials are flammable and they are able to continue to burneven though they are kept away from fire. In practical application, this shortcoming ofpolymer materials causes a great security risk and seriously threatens the safety ofpeople’s lives and property. Because the traditional PVC cable materials contain alarge number of plasticizers and chlorine, they are flammable and can release a lot ofsmoke and toxic gases when burning, which would suffocate people. Due to thepromulgated EU’s RoHS Directive and the enhanced awareness of environmentalprotection, the PVC cable materials are more and more restricted in application.Therefore, the strategic measure for preventing and reducing fire accidents is todevelop new-type high-temperature resistant and halogen-free flame retardant cablematerials, which has important theoretical and practical significance.Flexible poly (2,6-dimethyl-1,4-phenylene oxide)(PPO) is a composite blendedby PPO, rubber and thermoplastic elastomer, in which PPO phase has increasedflexibility and elastomer phase has improved heat-resistant and flame retardantproperties. Flexible PPO is an alternative to traditional halogen-free wire toeffectively solve the problems in difficultly balancing fire-retardation, flexibility,heat-resisting property, environment-friendly performance and other physicalproperties, which endows flexible PPO greater competitive advantage. In this thesis,flexible PPO/elastomer composites having excellent performance were prepared bymelt blending and dynamic vulcanization methods using PPO and styrene-butadienerubber (SBR) or SEBS (styrene-b-ethylene/butylene-b-styrene triblock polymer) asraw materials respectively. Based on the processing method, the ratio of rubber andplastics and vulcanization system of PPO/PS/SEBS composite, systematical andin-depth study was carried out on the phase evolution in the dynamic vulcanizationprocess, the relationship between structure and performance, and also, a detailed studywas conducted on the flow properties of processing, aging resistance, flameretardation performance and mechanisms of the PPO/SEBS composite. Specificresearch work mainly includes the following four aspects.1. The PPO/PS/SBR composites were prepared by dynamic vulcanization technology.The structure formation and evolution of the PPO/PS/SBR composite, in addition with the relationship between structure and properties were studied systematically.The analysis on microstructure shows that with a specific composition thebicontinuous phase structure of dynamic vulcanization PPO/PS/SBR systemtransforms into “sea-island” structure, in which the continuous matrix is constitutedby PPO/PS phase and the dispersed phase is constituted by the vulcanized SBRparticles. SEM, AFM and DMA analysis shows that PPO and PS are compatible andthey are partially compatible with SBR. Through dynamic vulcanization processing,the plastic matix are more compatible with the rubber phase so that blur phaseinterface could be formed and it is the ideal structure for rubber phase toughening.2. Systematical study was carried out on the effect of the processing parameters, theratio of rubber and plastics, vulcanization system and crosslink density on thestructure and performance of PPO/PS/SEBS composite. When the weight ratio ofSBR rubber reaches60wt%, composite material having excellent overall performancecould be obtained after blending for8min at200oC using sulfur as vulcanizing agent.In this composite, the vulcanized SBR rubber particles are uniformly dispersed in thePPO/PS matrix.3. The PPO/SEBS composite material is prepared by melt blending. The effect ofplasticizer (paraffin oil, naphthenic oil, aromatic oil) and flame retardant plasticizer(resorcinol tetraphenyl phosphate, RDP) on structure, mechanical properties,rheological properties, aging resistance, high temperature performance for compositematerials were studied in detail. Composite having good processability and lowhardness could be prepared.4. Using a variety of inorganic phosphorus flame retardant and minerals(montmorillonite, talc, silica and mica) as flame retardant, PPO/SEBS compositeshaving good flame-retardation property and overall mechanics properties are obtained.The LOI of composite can reach50.8and the flame retardation can pass UL94V0grade. In addition, the mechanical properties, flame retardation and thermal propertiesof composite were studied while phosphorus-based flame retardants and mica wereused as complex flame retardant.5. Basing on a variety of analytical methods, synergistic flame retardation and smokesuppression mechanism were in depth studied using phosphorus-based flameretardants and mineral mica as complex flame retardant. The synergistic indexbetween two flame retardants is calculated. Mica and RDP as complex flame retardantchanges the PPO degradation mechanism, reduces the degradation rate of PPO/SEBS substrate and increases the amount of carbon residue to form a dense carbon layer.RDP and mica effectively improve the flame retardation of PPO/SEBS composites bysynergistic effect through both the gas and solid phase. Compared with otherinorganic minerals, the dense char layer of residual carbon is a key factor to improveflame retardation in mica system.