| Thermoplastic vulcanizate(TPV)is a kind of thermoplastic elastomer prepared by blending and subsequent dynamic vulcanization technology.Because of its combined excellent properties of both cross-linked rubber and thermoplastic,it has received extensive attention in the fields of medical,electronics,and auto parts and so on.At present,the preparation of common TPV,such as ethylene-propylene diene monomer(EPDM)/polypropylene(PP)TPV,brominated isobutylene p-methylstyrene copolymer(BIMSM)/PP TPV and bromobutyl rubber(BIIR)/PP TPV,has been studied in detail,but its performance can not meet the higher requirements.Compared with the development of new TPV system,post-processing modification is a simple and efficient means to improve the performance of TPV.This paper focuses on the study of TPV phase morphology regulation and continuous phase crystallization regulation.The main research results are as follows:Studies have shown that BIMSM/PP TPV is similar to EPDM/PP TPV,and its micro rubber phase is the aggregate of rubber nanoparticles with a diameter of about 40 nm.For the post-processing modification of BIMSM/PP(65/35)TPV,while strengthening the shear action to break the rubber nano particle aggregate,an appropriate amount of star styrene ethylene/butene styrene block copolymer(Star-SEBS)is introduced as the third component with high viscosity,which can promote the transmission of shear stress in TPV and effectively inhibit the re agglomeration of shear dispersed rubber nano particles with the spatial barrier effect of high viscosity particles,Thus,a finer phase structure is obtained.It was found that when 10 wt%star SEBS was added,the size of rubber nano particle aggregate of BIMSM/PP(65/35)TPV increased from 1.31μm down to 0.85μm.While the elastic and rheological properties have no obvious change,the air tightness of TPV film is increased by about 21%,and the tensile strength and elongation at break are increased by 18%and 20%respectively.For the post-processing of BIMSM/PP(55/45)TPV,while strengthening the shear action to break the rubber nano particle aggregate,an appropriate amount of linear styrene ethylene/butene styrene block copolymer(Linear-SEBS)is introduced as the interface coating agent to coat the broken nano particle aggregate and effectively inhibit the agglomeration,so as to obtain a finer rubber dispersed phase morphology.The adhesion distribution of PP phase,BIMM rubber phase and phase interface was characterized by quantitative nanomechanics method of atomic force microscope.It was confirmed that Linear-SEBS could coat BIMSM nanoparticle aggregates.It was found that when 2 wt%linear SEBS was added,the size of BIMSM/PP(55/45)TPV rubber nano particle aggregate increased from 1.21μm reduced to 0.76μm.The thickness of rubber plastic interface increased by about 68 nm,which increased the tensile strength and elongation at break by 25%and 19%respectively,and also improved the elasticity and air tightness.Introducingβ-nucleating agent(TMB-5)into BIIR/PP TPV to induce the formation ofβ-crystals to prepare high-performanceβ-type BIIR/PP TPV product.BIIR/PP TPV obtained high content ofβCrystal,but its total crystallinity and phase state remain unchanged.Through performance comparison,it is found that the tensile strength,elongation at break,elasticity and gas barrier properties ofβ-type BIIR/PP TPV containingβcrystals are significantly higher than those of pure BIIR/PP TPV containingαcrystals.The continuous phase crystal structure was characterized by polarizing microscope(PLM)and scanning microscope(SEM)It was found that the crystals in the BIIR/PP TPV with the addition ofβnucleating agent were refined,the internal lamellar structure of the crystals was looser,and there are obvious lamellar connections between the crystals,which enhances the crystallization integrity.The structural changes and deformation mechanisms of pure BIIR/PP TPV andβ-type BIIR/PP TPV during deformation were studied in detail by atomic force microscopy nanomechanical mapping.The mechanism of simultaneous improvement of mechanical properties,elasticity and gas barrier properties of BIIR/PP TPV was revealed.An amide nucleating agent(TMB-5),was used to prepare EPDM/PP TPV withβcrystals and constant total crystallinity.Differentβcrystal morphologies can be obtained by changing the final melting temperature.Compared with pure EPDM/PP TPV,the mechanical strength and elasticity ofβ-type EPDM/PP TPV were significantly improved.With the increase of final melting temperature(T_f),three types ofβcrystal morphologies,namelyβspherulites,βtransverse crystals andβflower-like grain aggregates,were formed,respectively.The results show thatβtransverse crystals are more conducive to the improvement of the mechanical strength ofβ-type EPDM/PP TPV,whileβflower-like grain aggregates are more conducive to the improvement of elongation at break and elasticity ofβ-type EPDM/PP TPV.The dissolution and self-assembly behaviors ofβnucleating agents in EPDM/PP TPV melts were investigated by variable temperature FT-IR and found to be related to hydrogen bond dissociation/association.On heating,the C=O···H-N hydrogen bonds in the TMB-5 crystals dissociate and generate"free"TMB-5 molecules in the EPDM/PP TPV melt,resulting in TMB-5 in the EPDM/PP TPV"dissolved"in the matrix.During cooling,directional hydrogen-bonding associations guide the self-assembly/recrystallization of“free”TMB-5 molecules into supramolecular aggregates(differently shaped nuclei),thereby inducing the formation of differentβcrystal morphologies in TPV. |
