Preparation, Structure And Properties Of Functional EVA/NBR TPV And HIPS/SBR TPV

Thermoplastic vulcanizate (TPV) based on ethylene-vinyl acetate copolymer(EVA)/nitrile-butadiene rubber (NBR) blends and high impact polystyrene(HIPS)/styrene butadiene rubber (SBR) blends were prepared by dynamicvulcanization. The morphology, mechanical properties and dynamic viscoelasticbehavior such as Payne effect, Mullins effect and stress relaxation of TPV wereresearched systematically. The influences of the ratio of rubber and plastic,reinforcing agents and compatibilizer on the properties of TPV were investigated.The water-swellable EVA/CM/NBR TPV was prepared. It was found that the varietyand content of water-swellable material, together with the water absorptionenvironment, play an important role on the water-swellable behaiver greatly. Waterretent ability, repeated water swellable behavior, crystallization behavior and themorphology before and after water absorption on water absorption were also studied.The thermoplastic elastomer (TPE) based on the composites of EVA and wastenitrile-butadiene rubber powder (WNBRP) via melt-compounding. The interfacecompatibility, mechanical properties, dynamic viscoelastic behavior and themorphology were researched. The conductive polymer based on TPV was preparedby incorporation with carbon black (CB). The NTC effect, space charge distributionand dielectric properties of the composites were also investigated. The results wereas follows:(1) EVA/NBR TPVs with different weight ratios and different compatibilizercontents were prepared by dynamic vulcanization; the mechanical properties,crystallization behavior and morphology of the prepared EVA/NBR TPVs wereinvestigated systematically. When the CM was added into the EVA matrix as acompatibilizer, the tensile set at break and tensile strength were improved remarkably. The FE-SEM results showed that the fracture surfaces of TPVincorporated with CM were relatively flat and thinning tearing strips on the fracturesurface can be observed. The vulcanized NBR particles with the diameter of10μmwere dispersed evenly on the surface of etched TPV. And the aggregates of lamellarcrystals in EVA spherulites could be observed apparently.(2) The reinforecement influences of ZDMA, CB, and SiO2filled in the NBRrubber on the properties of the EVA/CM/NBR TPV were investigated systematically.For the ZDMA reinforced TPV, DCP vulcanization system showed more obviousimprovement of mechanical properties than that of sulphur vulcanization system.The tensile strength and tear strength of the TPV were improved obviously witheven low incorporaton with ZDMA. Increasing the strain, the storage modulus of theTPV deceased greatly and showed the Payne effect. The variation of storagemodulus and loss moludus could be fitted well by Kraus model. ZDMA reinforcedTPV process apparent Mullins effect. Compared with the unreinforced TPV, ZDMAreinforced TPV show larger maximum stress and other enhanced mechnical behaviorsuch as residual deformation, internal friction loss, tanδ and softening factor. Thevarious rule of stress relaxation could be fitted well by using five elements genernalMaxwell model. The FE-SEM and EDS results showed that the ZDMA particlescovered by NBR particles were dispersed on the surface of etched TPV.Incroporated with the60phr CB fillied in NBR, the tensile strength ofEVA/CM/NBR/CB TPV achieved the maxmium value. The fracture surfaces ofTPV reinforced by CB were relatively flat, and no obvious tearing strips could beobserved on the fracture surface. Incroporation with the40phr SiO2, the tensilestrength of EVA/CM/NBR/SiO2TPV arrived the maxmium value. The fracturesurfaces of EVA/CM/NBR/SiO2TPV were also relatively flat but obvious tearingstrips on the fracture surface could be observed. The NBR rubber phases weredispersed on the surface of etched TPV.(3) A novel water-swellable rubber (WSR) was prepared by dynamicallyvulcanized EVA/CM/NBR blends where crosslinked sodinm polpacrylate (CPNaAA)was used as a super water-absorbent resin and dispersed in the NBR rubber. Theresults showed that with the increase of CPNaAA dosages, the mechanical propertiesof the WSRs were decreased slightly; however, water-swelling properties of theWSRs were increased significately. The water-swelling ratio of WSRs with50phrCPNaAA was669.3%at120h. The WSRs with60phr CPNaAA showed high water-swelling rate and achieved the swelling equilibrium about566.3%at23h.The secondary and third water-swelling behaviors of WSRs showed significantlyrapid equilibrium swelling and remarkable decreasing of weight loss. Morphologicalstudy of etched surface showed that the CPNaAA particles were dispersed evenly inthe WSRs and coated with crosslinked NBR rubber. Furthermore, some significantgaps and large cavities could be found in the surface of dried TPV. The resultindicated that leading to the high equilibrium swelling rates in the second and thirdwater-swelling behaviors. The water-swelling ratio of EVA/CM/NBR/CPNaAATPV decreased greatly in the salt or acid solutions when the medium concentrationincreased. However, the water-swelling ratio of EVA/CM/NBR/CPNaAA increasedslightly at low concentration of alkaline solution, which was caused by ionizes of thecarboxylicion, indicating the weak alkaline environment can promote thewater-swelling ability of the TPV, which should be caused by improvement ofosmotic pressure, due to the acid-base reaction of–COOH and NaOH. TheEVA/CM/NBR/CPNaAA/in-situ NaAA WSR prepared by in-situ method andblending NaAA combined with CPNaAA method. With the increase of in-situ NaAA,the water-swelling ratio of WSR was increased and the weight ratio was decreased.(4) TPE based on EVA/WNBRP composites were prepared bymelt-compounding and the composites were compatibilized by CM. Experimentalresults indicated that CM had a good compatibilization effect on the composites.Compared with those of EVA/WNBRP composites, the tensile strength and theelongation at break of EVA/CM/WNBRP composites were increased significantly.When the CM content is15phr, the tensile strength and the elongation at break wereincreased by40.0%and307.8%, respectively. Morphology study showed the edgesof the irregular structures on the fracture surface of the EVA/CM/WNBRPcomposites were somewhat smoother, indicating the reason for the improvedelasticity. A softening phenomenon could be observed in the stress-stretch curves ofEVA/WNBRP and EVA/CM/WNBRP composites during the uniaxialloading-unloading cycles. Compard with uncompatibilized EVA/WNBRPcomposites, compatibilized EVA/WNBRP composites had the relatively lower stressand internal friction loss at specific stretch.(5) HIPS/SBR TPVs with different weight ratios and compatibilizer contentswere prepared by dynamic vulcanization. The mechanical properties andmorphology of the prepared HIPS/SBR TPVs were investigated systematically. And the SBS was added into the HIPS matrix as a compatibilizer, the tensile set at breakand tensile strength were improved. The FE-SEM result showed that the fracturesurfaces of TPV incorporated with SBS were relatively flat; thinning tearing stripson the fracture surface can be observed. The vulcanized SBR particles weredispersed evenly on the surface of etched TPV. Under the strain scanning mode, thestorage modulus of HIPS/SBR TPVs and HIPS/SBS/SBR TPVs decreased obviouslywith the increase of strain, indicating the obvious Payne effect. The storage modulusand loss moludus changes could be fitted well by Kraus model. Compared with theexperimental data tested under80oC, the storage modulus and loss modulus of TPVswere decreased obviously under100oC. A softening phenomenon could be observedin the stress-stretch curves of HIPS/SBR and HIPS/SBS/SBR TPVs during theuniaxial loading-unloading cycles. Compared with the uncompatibilized HIPS/SBRTPV, compatibilized HIPS/SBR TPV had the relatively lower stress and internalfriction loss.(6) The conductive polymer composites were prepared where as the CB wasused as conductive filler in the matrix of the EVA/CM/NBR TPV. The NTC effectand the dielectric properties of TPV/LDPE double samples were studied. The NTCeffect was remarkably showed when the CB content was14phr, about two orders ofmagnitude. When the CB content in TPV10phr, the amount of space chargeinjected into EVA/CB/CM/NBR TPV semi-conductive layer/insulating layer doublesamples is lowest. With the increase of the electric field frequency, theperrrimittivity of semi-conductive layer/insulating layer double samples decreased.With the increase of the electric field frequency, tanδ of EVA/CB/CM/NBR TPVsemi-conductive layer/insulating layer double sample was increased and tanδ ofEVA/CM/NBR TPV semi-conductive layer/insulating layer double sample achievedto the highest when the frequency is10Hz.