Study On Multi-Network Structure In Zinc Methacrylate / EPDM Composites

Because of the stable molecular structure,EPDM has excellent resistance to ozone,heat resistance,weather resistance,chemical resistance and many other advantages.It has become one of most used rubber in non-tire rubber products and been widely used in various fields.With the increasingly high technical requirements of the industry,the traditional carbon black and white carbon black reinforced system has been unable to meet the requirements.Due to the unique reinforcement characteristics,unsaturated carboxylic acid metal salts have been applied to more and more rubber products.In this paper,EPDM / ZDMA composites were prepared by direct filling method and in situ generation method.The difference of reinforcing effect was analyzed by vulcanization property and physical and mechanical properties.The mechanism of reinforcement effect of ZDMA on EPDM and the evolution of multiple network structures in composites were studied by using RPA,DSC,POM,XRD,TGA and in situ FTIR.It is found that reducing the initial size of dispersed ZDMA particle in EPDM is an effective means to improve the reinforcing effect.A series of methods including the introduction of polarities,increasing the polarity of ZDMA and EPDM,the use of filled paraffin oil and the use of OPE,EVM,EPDM-g-MAH,and in situ BMA modified EPDM were employed to improve the dispersibility of ZDMA in EPDM.The dispersibility of ZDMA was characterized by SEM and RPA.At the same time,the influence of various schemes on the multiple network structure in ZDMA/EPDM composites was investigated by the Mooney-Rivilin equation.Finally,the mechanism of ZDMA reinforced EPDM is explained from the view of network structure.In this paper,the two grades of ZDMA raw materials were characterized and applied experimentally.The results were compared with that of N330.Moreover,the two grades of ZDMA were applied combined with N330.The results show that both kinds of ZDMA are polycrystalline powders mixed by rod-like and bulky particles.The particles size is 10-30μm.TGA curves have two weight loss steps.There is no melting phenomenon within 250 °C.Compared with the N330,both grades of ZDMA have excellent processability and reinforcement in EPDM.The vulcanized rubber not only has high tensile strength,high tear strength and high hardness,but also maintains a high resilience and elongation at break.Moreover it has excellent heat aging resistance.According to the strain dependence analysis of the shear modulus G’ at low strain,the threshold of ZDMA forming the packing network in EPDM is 30 phr.The combination of N330 and ZDMA to reinforce EPDM forms a double filler network of carbon black and ZDMA,which play a synergistic effect.With the increase in the amount of carbon black,vulcanized rubber tensile strength,tear strength and hardness increased and tear elongation decreased.The results of the Mooney-Rivilin equation show that this is related to the enhancement of the filler-rubber network in the composite.In order to obtain better dispersion and reinforcing effect,ZDMA reinforced EPDM was formed in situ during the mixing process by using Zn O and MAA.The results show that large amount of reinforcement particles with size of 0.2~0.5μm was formed in the vulcanized rubber.Particles with larger size were rarely seen.When the molar ration of Zn O/MAA was 0.75,the tensile strength and tear strength of vulcanized rubber reached to 28.4MPa and 63.9KN.m-1 respectively,which were improved by 65% and 95% respectively compared to the results of ZDMA/EPDM obtained by directly fill method.The results of the Mooney-Rivilin equation show that in situ formation of ZDMA can form a better filler-rubber network.From the point of view of network structure,the most effective way to improve he reinforcement effect of ZDMA on EPDM is to reduce the initial size of ZDMA and improve the dispersibility of ZDMA in EPDM.Several methods including the use of filled paraffin oil,combine with OPE wax and combine with EVM and EPDM-g-MAH can improve the dispersion of ZDMA in EPDM.However these methods will cause compatibility and co-vulcanization problem of two rubber matrix.In order to avoid the compatibility problem,EPDM was melt grated with BMA.UV/IR double detector GPC proves BMA has been successfully grated with EPDM.RPA strain scan and Mooney-Rivilin curve show that the polarity of BMA greatly improves the dispersion of ZDMA in EPDM,weakens the Poly-ZDMA fillers network and strengthens the Poly-ZDMA-rubber network.The physical and mechanical properties of vulcanized rubber properties are improved greatly.Meanwhile,SEM images show the particles size of Poly-ZDMA in EPDM-g-BMA/ZDMA vulcanized rubber is 20 to 30 nm and the size of Poly-ZDMA aggregates is less than 10 μm.Melt grated with BMA is an effective means to improve the reinforcement effect of ZDMA.Finally,reaction kinetics of ZDMA/EPDM system was studied by Friedman method and Ozawa-Flynn-Wall method.The results show that ZDMA crystals self-polymerize to form amorphous Poly-ZDA initiated by DCP.The activation energy of this reaction is lower than that of covalent cross-linking reaction of EPDM.The final evolution of ZDMA reinforced EPDM network structure is: ZDMA crystals on the surface of aggregated ZDMA particles first polymerize initiated by DCP and then graft with EPDM to form a suspension side chain.This suspension side chain combination terminates with the EPDM macromolecular chain to form a covalent crosslinking network,or evolved into interpenetrating network of covalent crosslinking network and ion crosslinking network,the main reinforcement network,due to the strong ion interaction of Zn2+.The ZDMA crystals in the ZDMA particles can only self-polymerize to form Poly-ZDMA particles due to the difference of the polarity between the ZDMA and EPDM,and are clustered together to form a fragile filler network.