Enhancing mechanical performance of polylactide by tailoring crystal morphology and lamellae orientation with the aid of nucleating agent

• Published in: Polymer (Guilford) 2014-12, Vol.55 (26), p.6924-6934
• Main Authors: Bai, Hongwei, Huang, Chunmei, Xiu, Hao, Zhang, Qin, Fu, Qiang
• Format: Article
• Language: English
• Subjects: Applied sciences; Crystal morphology; Crystal structure; Exact sciences and technology; Injection molding; Lamellar structure; Mechanical properties; Melts; Morphology; Nucleating agent; Organic polymers; Orientation; Physicochemistry of polymers; Polylactide; Polylactides; Properties and characterization; Shear flow
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2014.10.059

The performance of semicrystalline polymers is significantly dependent on the crystal morphology and lamellae orientation. In this work, the crystal superstructure and mechanical properties of polylactide (PLA) with different amounts of nucleating agent (tetramethylene-dicarboxylic dibenzoyl-hydrazide, TMC-306) were investigated. It was found that TMC-306 can be dissolved in PLA melt and re-crystallize into fibrils upon cooling. These fibrils can serve as nucleation templates to induce the crystallization of PLA on their surface, resulting in a large enhancement in crystallization rate. More importantly, PLA lamellae can grow perpendicular to the long axis of TMC-306 fibrils, inducing the formation of shish-calabash, shish-kebab and needle-like structures, depending on the concentration of TMC-306 used. Taking advantage of shear flow experienced in injection molding, TMC-306 fibrils tend to align in PLA melt along the shear flow direction, inducing the formation of highly orientated PLA lamellae in injection-molded articles. In this way, a simultaneous improvement in impact toughness, tensile strength and elongation at break is achieved. This work provides a good example of using a fibrous nucleating agent as a template to tailor the crystal morphology and lamellae orientation, thus achieving greatly enhanced properties for PLA. [Display omitted] •Nucleating agent was used as a robust template to tailor the crystal superstructure.•PLA injection-molded bars with highly orientated lamellae were prepared.•Effect of crystal superstructure on the mechanical properties of PLA was studied.•Lamellae orientation imparts the bars with greatly improved mechanical properties.•We provide a guideline for preparing high-performance PLA injection-molded articles.