Research On The Effect Of Palladium Compounds On The Crystallization Of Poly(L-lactic Acid)

As one of the most popular biodegradable and thermoplastic materials,Poly L-lactic acid(PLLA)would be widely used in packaging,health care and food industry fields in future.Due to its high glass transition temperature(Tg)and slow crystallization rate,it is very difficult to crystallize quickly in the molding,So the products that have a low crystallinity have poor thermal-mechanical properties?mechanical property etc.Those shortcomings greatly limit its application.Adding effective nucleating agent is a common way to improve crystallization of PLLA,but the PLLA used nucleating agents with high performance are few,and nucleation mechanism is not clear Therefore,it's very significative to study the interaction mechanism between nueleating agent and PLLA and develop the high performance PLLA used nueleating agents.In this work,three kinds of palladium compounds,Bis(triphenylphosphine)palladium(?)dichloride,1,4-Bis(diphenylphosphino)butane-palladium(?)chloride and palladium chloride,were selected to add to PLLA.PLLA/palladium compounds blend were prepared by melt blending based on different contents of palladium compounds,This work presented the effect of palladium compounds on the crystallization of PLLA.The main results were as follows:(1)The effect of palladium compounds on the crystallization of PLLA was studied.Results showed that palladium chloride,Bis(triphenylphosphine)palladium(?)dichloride hindered the crystallization,1,4-Bis(diphenylphosphino)butane-palladium(?)chloride promoted the crystallization.In the cooling crystallization process,when the amount of 1,4-Bis(diphenylphosphino)butane-palladium(?)chloride was 0.8%,the corresponding crystallization peak temperature(Tc)rose from 103.9? t0 126.6?,crystallinity(Xc)increased from 33.89%to 56.79%comparing to pure PLLA.All of which suggests 1,4-Bis(diphenylphosphino)butane-palladium(?)chloride was a new type of PLLA nucleating agent.(2)The Avrami equation,Jeziorny equation and Mo equation were used to analyze the isothermal crystallization kinetics and the non-isothermal crystallization kinetics of PLLA samples.The results showed that the crystallization half-time of PLLA was shorted from 26.1 min to 0.69min with the adding of 1,4-Bis(diphenylphosphino)butane-palladium(?)chloride at 128 ? and Avrami exponent n was between 3 and 4,Which implied the crystal morphology was spherulitic;In the same cooling rate,The value of kc of PLLA/1,4-Bis(diphenylphosphino)butane-palladium(?)chloride was bigger than pure PLLA's.Under the same crystallinity,The value of F(T)of PLLA/1,4-Bis(diphenylphosphino)butane-palladium(?)chloride was bigger than PLLA's.when crystallinity is 50%,The value of F(T)of PLLA was shorted from 12.67?/min to 7.16?/min with the adding of 1,4-Bis(diphenylphosphino)butane-palladium(?)chloride.XRD spectrogram of PLLA smaples proved the crystal form of PLLA was not change with the adding of 1,4-Bis(diphenylphosphino)butane-palladium(?)chloride,the crystal form of pure PLLA and PLLA/1,4-Bis(diphenylphosphino)butane-palladium(?)chloride was a crystal.(3)In the isothermal crystallization process,peak intensities of PLLA samples at 921cm-1;1208cm-1and 1455cm-1 were tested by FTIR and normalized.The order of pure PLLA was 1455cm-1>1208cm-1>921cm-1,which means pure PLLA mechanism demonstrated that the interchain interaction of-CH3 preceded the interchain interaction of COC and-CH3 to make the conformational of pure PLLA become orderly,then a short 103 helix emerges because of the interaction above,there would be ? crystal formed in the end.Conversely,the order of PLLA/1,4-Bis(diphenylphosphino)butane-palladium(?)chloride was 1208cm-1>1455cm-1>921cm-1,which means the mechanism showed that the interchain interaction of COC and-CH3 was followed by the interchain interaction of-CH3,there would be a crystal formed in the end.(4)The effect of melting behavior of PLLA samples was studied.The double melting peaks of PLLA/1,4-Bis(diphenylphosphino)butane-palladium(?)chloride could been explained by melting-recrystallization model.In the same cooling rate and heating rate,the degree of perfection of PLLA/1,4-Bis(diphenylphosphino)butane-palladium(?)chloride was bigger than pure PLLA's.