摘要聚乳酸(Poly(lactic acid), PLA)是过去十年来飞速发展的具有左右旋两种旋光性 的生物基可降解热塑性聚酯材料。更为引人关注的是左旋与右旋 PLA 共混物所形成 的立构复合晶有着比纯粹的左旋或者右旋 PLA 高出近 50 ℃的熔点，力学性能上也 存在一定的优势。随着聚乳酸立构复合晶的发现，对聚乳酸结晶度的控制以及对 PLA 结晶行为的深入理解有助于掌握其热性能、光学、力学等各种性能，从而进一步拓展 聚乳酸这种生物可降解材料的应用范围。83141

本 文 利 用 具 有 较 快 升 降 温 速 率 的 差 示 扫 描 量 热 仪 (Differential Scanning Calorimetry, DSC)研究了聚乳酸立构复合晶与均聚晶的结晶生长及成核动力学行为。 首先根据 PLA 复合晶及左旋均聚晶（PLLA）的基本热分析信息（Tg 与 Tm）确定了 需要考察的温度范围；其次，以特定的升降温程序确定了抑制 PLLA 与 PLA 共混物 的临界降温速率；最后，通过从熔体快速降温至给定的温度，考察了不同温度下 PLLA 与 PLA 共混物等温不同时间的后的冷结晶面积及等温过程中晶体生长的多少。根据 上述结果随等温时间的变化确定了半结晶生长时间与成核完成的时间，并对比了 PLDB 与 PLLA 的结晶生长动力学与成核动力学。

结果表明，PLLA 均聚晶在等温温度为 110 ℃时具有最快的结晶生长，PLDB 同 时在 110 ℃和 130 ℃具有结晶生长速率的极大值，分别对应于 PLDB 中均聚晶和立 构复合晶的生长。所以要从聚乳酸共混体系中得到较多的立构复合晶结构，要将等温 温度控制在 130 ℃左右。根据 PLLA 与 PLDB 生长和成核动力学的对比可以知道， PLA 共混物在等温结晶的过程中，首先生成的是立构复合晶，随后均聚晶的生长会 快于立构复合晶结构。由此可以得出，链间成核在热力学上占优，链内作用在动力学 上占优。

毕业论文关键词：立构复合晶；动力学；成核；结晶生长

Abstract Polylactic acid (Poly (lactic acid), PLA) is bio-based biodegradable thermoplastic polyester material with two optical rotation (PLLA and PDLA), and rapidly  developed over the past decade。 In addition, the blend of PLLA and PDLA (PLDB) with identical

weight forms the stereocomplex crystal (SC) which bearing a melting point 50  ℃  higher

than that of pure PLLA or PDLA, as well as more more excellent mechanical properties。 The regulation of the crystallinity and the comprehension of the crystallization behaviour should be essential for us to understanding the thermal, optical and mechanical properties and to expanding the application scope of this amazing biodegradable material。

In this thesis, special Differential Scanning Calorimetry (DSC) with higher scanning rates than conventional DSC had been applied to study the crystallization and nucleation kinetisc of both PLDB and PLLA。 Firstly, we had measured the basical thermal information, i。 e。 melting and glass transition temperature of both PLDB and PLLA。 Secondly, by using a pre-designed temperature program, we had determined the critical cooling rate for PLDB and PLLA, beyond which crystallization of them can be effectively forbided。 Finally, we had investigated and compared the crystallization and nucleation kinetics between PLDB and PLLA by inquiring the cold crystallization and the melting enthalpy on the heating curves after annealed at different temperature with specific times。

The results showed that, PLLA possesses the fastest crystallization and nucleation rate at around 110  ℃, while PLDB bears the two fastest crystallization and nucleation rate at

110 ℃ and 130 ℃, respectively。 For this two minimum of the half-crystallization time and nucleation time, we categorize the former correspanding to the homo-crystals (HC) in PLDB, and the latter the stereocomplex crystal (SC)。 Thus, we can learn that if one want to