Study On The Preparation And Properties Of TPI Microcellular Foams

Trans-1,4-polyisoprene?TPI?foams were prepared by supercritical microcellular foaming method using carbon dioxide?CO₂?as foaming agent,the effect of crystallization and crosslinking degree on the cell structure and shrinkage of the product were studied.The shape memory function of irradiated crosslinked TPI foams were also studied.Open-cell TPI microporous materials were prepared by phase separation and sol-gel method,the hydrophobic properties and oil-water separatiom were studied.Supercritical TPI microcellular foams were prepared through rapid pressure relief method,using supercritical CO₂ as foaming agent,sulphur content as a variable,the saturation pressure and temperature are 110?and 12MPa respectively,keeping TPI samples under the condition for 2h.The effects of crosslinking and crystallinity degree on cell structure,expansion ratio and shrinkage of products were studied by means of scanning electron microscope?SEM?,differential scanning calorimeter?DSC?and low field NMR.The results show that the foams are closed structure,with the increasing of sulphur content,the crystallinity decreased and the crosslinking increased.When sulphur content is 5phr,TPI became amorphous,foam density increased,the cell was changed from honeycomb to circular,and finally became star concave and collapse structure,the cell size and foaming ratio decreased,the cell density increased,and the cell wall became thicker.The shrinkage rate of the product increased from 5.5%to 52.4%,and the growth of the cell experienced two stages of constant temperature and cooling,the melt viscosity of the matrix with low crosslinking degree is lower and the resistance to the growth of the cell is smaller,the melt viscosity increased for TPI cooling crystallization with the decrease of temperature during the cooling process,the stress around the cell is concentrated,so the growth of the cell is restricted and the shape is fixed.It is found that the ratio of the axial expansion of the crystallized micro crosslinking foam material is in the strain range of the cold drawing stage in the stress-strain curve of the unfoamed material?the shape variable of the unfoamed material is in the cold drawing stage,and the deformation can not be recovered after the force removed?,and the deformation is similar to that of the unfoamed material does not recovered,therefore,the expansion ratio and shrinkage of foamed materials can be predicted through the tensile stress-strain curves of the unfoamed materials.Due to the suitable crystallinity and crosslinking degree of TPI with sulphur content of 3phr,the external pressure produced by melt strength is equivalent to the internal pressure of cells,the shrinkage rate of the material is lower,and the cell structure is the best.When the material is a rubber state that is not crystallized,Entropy elasticity makes the foams shrink rapidly during the cooling process,the shrinkage rate is up to 52.4%,and the size is close to the unfoamed material.Supercritical TPI microcellular foams were prepared through rapid pressure relief method,using supercritical CO₂ as foaming agent,irradiation dose?30kGy-150kGy?as a variable,the saturation pressure and temperature are 110?and 14MPa respectively,keeped TPI samples under the condition for 2h.The effects of irradiation dose on the cell structure,expansion ratio,shape memory and dielectric properties were investigated by SEM,DSC,infrared spectrum?FTIR?,low field NMR,DMA and broadband dielectric spectroscopy.The results show that the crosslinking degree increased,and the crystallinity of the material first decreased and then increased?the change range was only 3.6%?with the increase of irradiation dose,the cell size and expansion ratio decreased,the foams density increased.Untreated TPI and irradiated TPI foams can achieve 100%deformation fixation rate by controlling deformation fixation time,however,the untreated TPI had a deformation recovery rate of 0%,the recovery rate of the material increased with the increase of radiation dose,it can be seen from the variation trend of dielectric constant and dielectric loss that the introduction of cells can greatly improve the insulation performance of materials,but,because the cell size decreased with the increase of radiation dose,so the material of the dielectric constant and the dielectric loss increased slightly,but the change was not apparently.TPI open-cell mataerials were prepared by phase separation and sol-gel process,taking dichloromethane as solvent,absolute ethyl alcohol as phase separation agent which is used as a variable.The contact angle measuring instrument and SEM were used to test the foam morphology and the hydrophobicity of the surface and tearing surface,and the oil-water separation performance was studied by the oil-water separation experiment.The results show that with the increase of the phase separation agent,the foam density is smaller,the cell size is larger,the surface of the material changed from smooth to rough,the contact angle of the surface and the tear surface firstly increased and then decreased,the contact angle of the tearing surface is more than 150°,it means the superhydrophobic ability is given,when TPI:dichloromethane:absolute ethyl alcohol=1:12:1.5,the surface of the material also has superhydrophobic function.,the contact angle is as high as 153.5°.Through the oil and water separation experiment,it is found that the 2.314g TPI superhydrophobic open-cell material with the diameter of 32mm can absorb 5ml hexane in 4min,and the TPI open-cell material full of organic solvents still has a strong superhydrophobic property.