The Research Of Thermosensitivity Modification On Polyolefine

Polyolefin is widely used in our daily life because of its rich source,low cost,easy processing and excellent performance.On the other hand,polyolefin is nonpolar polymer,and its surface is inert.Its adhesion,dyeing and hydrophilic properties which all are poor limit the application.Thus the modification of polyolefin has become a research hotspot.Poly（N-isopropyl acrylamide）（PNIPAAm）as a thermo-responsive polymer contained hydrophilic group（—CONH—）and hydrophobic group [—CH（CH3）2],which is grafted on the surface of polyolefin material enables the polyolefin to be thermo-response while widening the application of PNIPAAm and polyolefins.In this paper,PNIPAAm was synthesized by UV irradiation.Its structure was characterized by FTIR,and the thermo-response of PNIPAAm was studied by modulation DSC（MDSC）.From the test results,PNIPAAm with low critical solution temperature（LCST）at about 33 ℃ was successfully synthesized under the experimental conditions.Using NIPAAm as monomer and benzophenone（BP）as photosensitizer,LDPE-gPNIPAAm grafted polymer was prepared by two-step surface photografting.The apparent structure and molecular structure of LDPE-g-PNIPAAm were characterized by scanning electron microscopy and infrared spectroscopy.Thermo-response of LDPE-g-PNIPAAm was tested by surface water contact angle measurement and MDSC.The effects of photosensitizer concentration,photo reduction time,monomers concentration and UV light irradiation time on the grafting ratio were discussed.From the test results,the LDPE-g-PNIPAAm showed thermos-responsive hydrophilicity/hydrophobicity and its LCST is about 33 ℃.With the increase of photosensitizer concentration,monomers concentration,and UV light irradiation time in the system the grafting ratio was increased.And with the increase of photo-reduction time,the grafting rate is increased to a certain value and tends to stabilize.The grafting rate of the LDPE,s surface can be controlled by adjusting these four factors.PP-g-PNIPAAm is successfully obtained by two-step surface photo-grafting.Infrared analysis and scanning analysis show that this method is versatile for graft modification of polyolefins.The results of MDSC and water contact angle measurements show that PP-g-PNIPAAm has thermos-responsive hydrophilicity/hydrophobicity and its LCST is about 33℃.The results of the discussion on the factors affecting the grafting rate are known,the grafting ratio is increased with the increasing of photosensitizer concentration,grafting monomer concentration and UV light irradiation time.But PP and LDPE show different grafting regular pattern in the photo-reduction stage.With the increase of photo-reduction time,the grafting ratio is increased first and then decreased,and the photo-reduction time has an optimal value.The grafting ratio of PP is higher than that of LDPE under the same grafting condition.PNIPAAm is successfully grafted on the surface of Nano-Cu/LDPE composites by two-step surface photo-grafting.Moreover,the composite material obtained the thermos-response and the LCST is about 33°C.The release rate of copper ions(Cu²⁺)of the composite after grafting was related to the amount of grafted PNIPAAm in the simulated uterine fluid.In the same corrosive environment,when the PNIPAAm completely covers the surface of the composite material,Cu²⁺ release rate has a smaller gap in the initial stage of soak with time increased.And the burst release phenomenon of Cu²⁺ is effectively alleviated.When PNIPAAm can not completely cover the surface of the composite material,Cu²⁺ release rate has a large gap in the initial stage of soak with time increased,and there is still more obvious burst release phenomenon.When the ambient temperature is lower than LCST,the addition of PNIPAAm can improve the hydrophilicity of the composites and increase the release rate of Cu²⁺ in the stationary stage.