Structure And Properties Of Functional PLA/NBR TPV With Co-continuous Structure

Thermoplastic vulcanizates(TPVs)based on polylactic acid(PLA)/nitrile butadiene rubber(NBR)were prepared via dynamic vulcanization.The mechanical properties,microstructure,morphology evolution,Mullins effect under compression mode and its reversibility behavior,stress relaxation behavior under compression mode and its reversibility behavior were investigated systematically.The degradation behavior of PLA was researched where the sample immersed in HCl solution,phosphate buffer solution,NaOH solution with different weight ratio respectively.In addition,TPV based on high density polyethylene(HDPE)/NBR was prepared via dynamic vulcanization,which was compatibilized with chlorinated polyethylene(CPE).And the influence of the dynamic vulcanization time on morphology evolution was initially explored.The main results were shown as below:(1)For PLA/NBR TPV,the mechanical properties of TPVs where dicumyl peroxide(DCP)was used as cross-linking agent were much higher than that of TPVs where sulfur was used as cross-linking agent.The strength of the TPV increased gradually with the increasing of the PLA content.When the dosage of zinc methacrylate(ZDMA)was increased,the strength of TPV was increased remarkably.It can be seen that the properties of TPV with incorporation of 8 phr ZDMA was better.Some mechanical behaviors of TPVs were improved with increasing dioctyl phthalate(DOP)dosage.The results of microstructure of etched TPV showed that a unique co-continuous structure was formed in PLA/NBR TPVs.The NBR phase in the etched sample surface had a continuous network structure and the width of grid was 0.3~0.5 ?m and the pore was 1~3 ?m.It should be pointed out that the width of grid was smaller,the size of pore was smaller and the network microstructure of theco-continuous phases was denser with increasing the dynamic vulcanization time or with incorporation of ZDMA.(2)For PLA/NBR TPV,incorporation in DOP or reducing PLA content in PLA/NBR TPV,the Mullins effect was weakened.Increasing the heat treatment temperature could improve the reversible recovery of Mullins effect.The stress relaxation results showed that the stress relaxation behavior of PLA/NBR TPVs were increased obviously with increasing PLA content in TPV.Increasing the heat treatment temperature or decreasing the PLA content in TPV,the reversibility of relaxation was improved remarkably.Compared with the recovery ability of traditional TPV with “sea-island” microstructure,the recovery ability of TPV with co-continuous microstructure was stronger.(3)The degradation behavior of pure PLA and PLA phase in PLA/NBR TPV was researched in 0.36 wt.% HCl solution,phosphate buffer solution,0.40 wt.% NaOH solution and 1.60 wt.% NaOH solution respectively.And the microstructure of TPV at different degradation time was also observed.The results showed that the degradation rate of PLA in 1.60 wt.% NaOH solution was most quick,followed by0.40 wt.% NaOH solution,then the 0.36 wt.% HCl solution and the phosphate buffer solution was slowest.The degradation rate was small at beginning and then increased in the degradation process.With the degradation of PLA,the pH of HCl solution gradually increased,the pH of NaOH solution gradually decreased and the pH of the phosphate buffer solution was maintained within a constant range.Morphology studies showed that the surface of the sample became rougher with the degradation time increasing.When the degradation time reached 120 days,the sample exhibited a continuous network microstructure and the mass friction of degraded PLA accounted for 96.6 % of the total PLA.(4)HDPE/NBR TPV was prepared via dynamic vulcanization which was compatibilized by CPE.The morphology evolution of HDPE/NBR TPV and HDPE/CPE/NBR TPV were studied.The results showed that HDPE/NBR TPV exhibited the “sea-island” microstructure.During the dynamic vulcanization process,NBR was sheared into particles and dispersed in the resin phase matrix.The size of dispersed phase was gradually reduced with the dynamic vulcanization time increasing.The size of the particles of the TPV with the incorporation of CPE was more uniform than that of the TPV without compatibilization.The particle size of TPV before compatibilization was between 20 ?m and 30 ?m.And the particle sizeof TPV after compatibilization was about 10 ?m.