摘要聚乳酸作为一种环保可再生的高分子材料，安全无毒，具有良好的可降解性和 生物相容性的特点，同时兼具有良好的物理性能和力学性能，广泛应用于医疗、农 业、纺织服装。组织工程材料等领域。然而，聚乳酸不易结晶，结晶速率慢，且其 熔点低，热稳定性差的缺点极大的限制了聚乳酸的应用。PLLA 和 PDLA 共混后会 形成立构复合物，其熔点比各自均聚物的熔点提高了 50℃左右，结晶速度加快，使 其热稳定性和结晶性能显著提高。因此，提高 PLA 的热稳定性以扩大其应用范围具 有极其重要的意义。83373

本论文采用溶液共混法将一组小比例的 PDLA 溶液与 PLLA 溶液充分混合，其 中 PDLA 的质量分数分别是 0%、2%、4%、6%、8%、10%，并用溶液浇膜法经挥 发成膜制备共混物。采用差示扫描量热仪(DSC)、偏光显微镜观察(POM)、X 射线衍 射(XRD)等手段研究小比例质量分数的 PDLA 对 PLLA 热性能与结晶行为的影响。结果表明，PDLA 加入到 PLLA 中，形成以 PLLA 为母体的立构复合晶体，立 构复合晶体扮演着成核剂的角色，充当 PLLA 的异相成核位置，促使结晶速率加 快，球晶减小，结晶行为显著增强。且这种增强行为随 PDLA 含量的增加而增加。 PLLA/PDLA 共混物的最佳结晶温度在 120℃，高于此温度结晶速率明显降低。且随 着 PDLA 含量的增加，熔体结晶温度由 109。32℃升高至 122。3℃，结晶峰面积也由 4。91J/g 增加到 8。48J/g， PLLA 的过冷度逐渐减小， 其中ΔTmc2 由 66。25℃减小到55。17℃。以上均说明加入 PDLA 使 PLLA 结晶性能明显得到提升。且当 PDLA 的含 量达到 4%及以上时，在 220℃出现了明显的熔融峰，熔点增加了将近 50℃，热稳定 性显著增强。

毕业论文关键词：立构复合；聚乳酸 ；结晶；热性能；小比例 PDLA

Abstract Polylactic acid, as an environmentally friendly, renewable, safe and nontoxic polymer material , has good biodegradability and biocompatibility characteristics。 At the same time, it has good physical and mechanical properties。 So it’s widely used in medical, agricultural, Textile and Tpparel Tissue engineering materials and  other  fields。 However, polylactic acid is difficult to crystallize。 Slow crystallization rate and low melting point, poor thermal stability drawbacks greatly limit the application of polylactic acid。 Formation of stereocomplex,  after  blending   PLLA  and   PDLA,  makes  the   melting   point   of    the

stereocomplex      increased   about   50   ℃,   compared   to   the   melting   point   of  each

homopolymer。 Its crystallization is speeded, so the thermal stability and crystalline properties are improved significantly。 Therefore, it’s extremely important to improve the thermal stability of PLA in order to expand its range of applications 。

In this paper, a small proportion of the PDLA solution is thoroughly  mixed with PLLA solution wherein PDLA mass fraction is 0%, 2%, 4%, 6%, 8%, 10%,which is called solution blending method。 We cast film volatile via film-forming method  by  making blends。 Small-scale research on the mass fraction of PDLA, PLLA thermal properties and crystallization behavior are researched by means of differential scanning  calorimetry (DSC), polarizing microscopy (POM), the impact of X-ray diffraction (XRD) 。

The results showed that when PDLA is added to the PLLA,  the  stereocomplex crystals forms while PLLA as a precursor。 Stereocomplex crystal acts as a nucleating agent and nucleation sites in the heterogeneous crystallization of the PLLA。It can accelerat the crystallization rate, and reduce the size of spherulite。 Crystallization behavior is significantly enhanced, too。 This enhanced behavior increases with the incresing of the content of PDLA。 The optimum crystallization temperature of PLLA / PDLA blend is 120 ℃。 Above  this  temperature, the  crystallization rate will  be  significantly  lower。 With the  increase  of  the  content  of  PDLA,  melting  crystallization  temperature  increases to 122。3 ℃, from 109。32 ℃。 But also the peak area of crystallization added to 8。48J / g, from 4。91J / g。 During the process, the degree of undercooling of PLLA diminishes。 With the  decrease  of  the  undercooling   degree,  the  ΔTmc2  decreased  to  55。17  ℃,     from 2 66。25 ℃。 Described above are added to that PDLA significantly improve crystallization behavior of PLLA。 When  the  content of PDLA is  4% or above,  there is  a clear    melting