| Thermoplastic elastomers(TPEs)based on high-density polyethylene(HDPE)/waster ground rubber tire powder(WGRT)compounds were prepared by melt-compounding,and styrene-butadiene-styrene block copolymer(SBS)was used as compatibilizer.The mechanical properties,micro-morphology,compression stress relaxation and its reversibility,compression Mullins effect and its reversibility,compression set and its reversibility of HDPE/SBS/WGRT TPE were investigated systematically.The super-hydrophobic and super-oleophilic TPE surfaces were prepared by molding method,where metallographic sandpaper and etched aluminum foil were used as templates,respectively.The influence of the sandpaper types and the etching time of aluminum foil on the morphology and wettability of molded TPE surfaces were investigated systematically.Thermoplastic vulcanizates(TPV)based on HDPE/styrene-butadiene rubber(SBR)were prepared by dynamic vulcanization method,and the mechanical properties of HDPE/SBR TPVs were studied.Super-hydrophobic and super-oleophililc TPV surfaces were prepared by molding method,where sandpaper was used as template.The influence of abrasive particle size of sandpapers and the content of HDPE on the wettability of mold TPV surfaces,the reusability of sandpaper and the stability of super-hydrophobic and super-oleophilic TPV surfaces under high heat treatment temperature were investigated systematically.The results were shown as below:(1)Morphology studies on the tensile fracture surfaces,brittle fracture surfaces and etched surfaces of HDPE/SBS/WGRT TPEs showed that the morphology of uncompatibilized TPE surface was obviously different from that of compatibilized TPE surface.It could be found that uncompatibilized TPE surface was rough and on which the micro-sized fibrous structure could be found obviously,and the combination between WGRT particles and HDPE resin was not firm.However,it could not foundthe fibrous structure on the surface of compatibilized TPE,and the WGRT particles were firmly bond to HDPE resin,indicating that addition of SBS improved the elastic resilience of the plastic deformation of HDPE resin,as well as the interface bonding effect between WGRT particles and HDPE resin.Moreover,the lamellar structure of the HDPE spherulites was observed on the etched TPE surface,and its slip and rotation led to micro-sized fibrillar structure,which were observed on the brittle fracture surface of TPE;and this micro-sized fibrillar structure was more obvious with addition of SBS.(2)Researches on the mechanical properties and viscoelasticity of HDPE/SBS/WGRT TPEs showed that the elongation at break of TPE was increased greatly with the increase of SBS,while the tensile strength and the tear strength were increased in a certain extent,and TPE showed better comprehensive mechanical properties with 12 phr SBS.Moreover,the stress softening phenomenon was observed obviously in TPE,that also called Mullins effect,which was weakened with the increase of SBS content.The stress relaxation of TPE could be divided into two stage:fast and slow stage,and the residual stress of TPE increased gradually with the increase of SBS content.In addition,the compression set of TPE was fitted by three-stage method and the fitting results were consistent with the initial data,and Maxwell model was used to quantitatively characterize the recovery time of compression set of TPE.Furthermore,the recovery ability of the compression Mullins,compression stress relaxation and compression set of TPE was enhanced in varying degrees with increasing heat treatment temperature and SBS content,and the recovery ability was the best at 120 ℃.(3)Super-hydrophobic and super-oleophilic TPE surfaces were prepared by molding method,and sandpaper and etched aluminum foil were used as templates.SEM studies on the templates and the molded TPE surfaces showed that the rough structure of molded TPE surface was not a simple replica of the templates surface.During the molding process,HDPE resin penetrated into the cracks among the rough structure of the templates,and the plastic deformation of TPE appeared during peeling progress,leading to the generation of fiber-like strips.The strips were intricate,and the gaps among them could intercept air to reduce the contact area between water droplet and TPE surface.Compared with that of flat TPE surface,the roughness of molded TPE surface was increased obviously,especially for the rough structure of the TPE surfaces molded with W7 sandpaper and aluminum foil etched for 12 min was the densest.Thewettability tests showed that molded TPE surface exhibited well hydrophobic and super-oleophilic properties,especially,the TPE surfaces molded with W7 sandpaper and aluminum foil etched for 12 min showed excellent super-hydrophobic and super-oleophilic properties,and the thickness of super-hydrophobic layer of TPE surfaces molded with W7 sandpaper and aluminum foil etched for 12 min were 60 μm and 103 μm,respectively.The super-hydrophobic and super-oleophilic behavior of molded TPE surface could be explained by Cassie model and Wenzel model independently.The gas/liquid interface ratios of super-hydrophobic and super-oleophilic TPE surfaces were calculated by Cassie model,which were all lager than 80 %;moreover,the flat TPE surface showed oleophilic property,according to Wenzel model,the oleophilic surface could change into super-oleophilic surface with the increase of roughness.(4)HDPE/SBR TPVs were prepared by dynamic vulcanization,and the studies on mechanical properties of TPVs showed that HDPE/SBR TPVs all exhibited elastomric properties until content of HDPE was 50 phr;moreover,the elongation at break,tensile strength and tear strength of TPVs were increased greatly with the increase of HDPE content,and HDPE/SBR TPV with weight ratio 50/50 had the best comprehensive mechanical properties.Furthermore,DSC test result showed that HDPE and SBR had good interface combination.(5)Super-hydrophobic and super-oleophilic TPV surfaces were prepared by molding method,where sandpapers were used as template.SEM studies on morphology of sandpapers and molded TPV surfaces showed that the roughness of the TPV surfaces was increased obviously after molded with sandpapers,especially after molded with W7 sandpaper,the micro-sized fiber-like strips could be observed obviously on the molded TPV surface.It should be noted that the fiber-like strips were generated from the plastic deformation of HDPE resin,and the gaps among the strips could intercept air to reduce the contact area between the water droplet and the TPV surface.According to Cassie model,the gas/liquid interface ratios of molded TPV surfaces were all larger than 80 %,while that of molded HDPE/SBR TPVs with weight ratio40/60,50/50 and 60/40 were 88.6 %,89.4 % and 90.3 %,respectively;moreover,the thickness of super-hydrophobic layer of HDPE/SBR TPVs with weight ratio 40/60,50/50 and 60/40 were 105.66 μm,108.45 μm and 111.32 μm respectively,indicating that the thickness of super-hydrophobic layer was increased slightly with increase HDPE content.The flat TPV surface showed oleophilic property,while the diffusionrate of liquid paraffin on the molded TPV surface was accelerated obviously,which exhibited super-oleophilic property,and this phenomenon could be explained by Wenzel model.Moreover,the surface energy test of TPVs surfaces showed that compared with that of flat TPV surface,surface energy of molded TPV surfaces were decreased significantly,especially that of TPV surface molded with W7 sandpaper was the lowest,indicating that lower surface energy and proper roughness could endow TPV surface with super-hydrophobic and super-oleophilic properties.Studies on the stability of super-hydrophobic and super-oleophilic TPV surface showed that the molded TPV surface still exhibited super-hydrophobic and super-oleophilic properties even the sandpaper template has been used for five times,indicating that sandpaper template had good reusability.Furthermore,when the heat treatment temperature was85 ℃ or lower,the molded TPV surface still showed super-hydrophobic and super-oleophilic properties;however,the wettability of molded TPV surface decreased significantly when the heat treatment temperature was 110 ℃ or 135 ℃,it was because that the fiber-like strips resulted from the plastic deformation of HDPE resin were recovered under high temperature.Accordingly the roughness of the molded TPV surface was reduced which led to poor wettability. |
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