摘要
通过溶液共沉淀-压板的方法,在聚乳酸混合物中形成了具备一定有序度的"准有序相",并基于此结构在聚乳酸的玻璃化转变温度附近进行拉伸形成了立构复合晶(SC晶).红外光谱的结果表明足够高含量的右旋聚乳酸是诱导形成SC晶的前提:5%含量试样在测试中没有获得SC晶,当含量高达20%时则可以通过低温退火或者拉伸处理试样来形成SC晶. 70°C退火时由于自成核作用以及准有序相的异相成核作用,往往伴随形成α'晶.在50°C拉伸时受限于链段活性只能形成中间相;在70°C时拉伸模式对诱导效果有很大影响.以较快速率(应变速率γ=0.06 s-1)拉伸可以诱导高纯度的SC晶,间歇性的拉伸会同时形成α'晶和SC晶2种晶体.
Adding stereocomplex（SC）crystals into matrix can effectively improve the hydrolysis resistance and heat-resistance of polylactic acid（PLA）.However,the existence of pre-formed SC crystals will increase the processing difficulty because a higher processing temperature is needed.Thus the exploration of inducing SC crystals via external force fields is important.In this paper,‘quenched’and‘annealed’PLA enantiomer mixtures were studied.The enantiomer mixtures were prepared by solution coprecipitation.Preparation of the‘quenched’specimen is done in two steps：hot pressed at 250°C for 5 min and then quenched in air（15°C）.The method of annealing is done as following：hot pressed at 250°C for 5 min,annealed at 200°C for 30 min,and finally quenched in air.The X-ray diffraction patterns indicated that a loose structure with low order degree,named as quasi-ordered phase（QOP）,was formed in the two types of the samples.Based on this structure,SC crystals was formed during stretching near the glass transition temperatureof PLA.The results of infrared spectra indicated that adequate amount of poly（D-lactic acid）（PDLA）is the prerequisite for the induction of SC crystals.There was no SC crystal generated in the specimens with 5%of PDLA,regardless of the treatment used.However,SC crystal appearred in the specimens with 20%of PDLA.This is because that adequate amount of QOP regions can merge and rebuild into complete crystals.In the specimens of high PDLA content,the transition could happen either during annealing or stretching above Tg（e.g.,70°C）.Owing to the self-nucleation and heterogeneous nucleation of QOP,α＇-form crystal would be formed concomitantly during annealling.Therefore the former approach cannot generate pure SC crystal.As to the latter approach,depending on the tensile temperature and rate,mesophase,SC crystal andα＇-form can be selectively generated.When stretched below Tg（e.g.,50°C）,only mesophase can be obtained beacause of low chain activity.As stretched at
作者
王刚
王柯
Gang Wang;Ke Wang(College of polymer science and engineering,Sichuan University,Chengdu 610065)
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
2018年第9期1221-1227,共7页
Acta Polymerica Sinica
基金
国家自然科学基金(基金号51373108)资助项目
关键词
拉伸
立构复合晶
红外光谱
准有序相
Tensile deformation
Stereocomplex
Infrared spectroscopy
Quasi-ordered phase
