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Low-Temperature Sintering of Stereocomplex-Type Polylactide Nascent Powder: Effect of Crystallinity
Macromolecules ( IF 5.1 ) Pub Date : 2017-09-29 00:00:00 , DOI: 10.1021/acs.macromol.7b01794 Dongyu Bai 1 , Huili Liu 1 , Hongwei Bai 1 , Qin Zhang 1 , Qiang Fu 1
Macromolecules ( IF 5.1 ) Pub Date : 2017-09-29 00:00:00 , DOI: 10.1021/acs.macromol.7b01794 Dongyu Bai 1 , Huili Liu 1 , Hongwei Bai 1 , Qin Zhang 1 , Qiang Fu 1
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Stereocomplex (SC) crystallization between high-molecular-weight poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) provides a promising route to substantially improve the properties of polylactide (PLA), but conventional melt processing of the SC-type PLA (SC-PLA) is nearly impossible primarily due to the poor crystallization memory effect as well as serious thermal degradation after complete melting of SC crystallites with high melting temperatures of above 220 °C. Recently, we reported an innovative low-temperature (180–210 °C) sintering technology for fabricating SC-PLA products from its nascent powder. Unfortunately, its practical application has been significantly hindered by an extremely high pressure of 1 GPa, which must be utilized to ensure good surface wetting of the densified powder particles. With this challenge in mind, herein, the role of powder crystallinity in the low-temperature sintering has been investigated. Interestingly, we first demonstrate that depressing powder crystallinity is favorable for the particle wetting under a much lower pressure during the densification stage of the nascent powders because the deformation of the powders becomes easier with the decrease in the fraction of rigid crystal network. Moreover, during the subsequent interface welding stage, more PLLA/PDLA chains could be involved in the interdiffusion and SC crystallization across particle interfaces, thus forming large amounts of new SC crystallites capable of tightly welding the interfaces. As a consequence, SC-PLA sheets with excellent heat resistance and mechanical properties have been successfully fabricated by sintering under a pressure of as low as 300 MPa. Overall, these fascinating findings not only provide new fundamental understandings on the role of initial crystallinity in the low-temperature sintering of SC-PLA powder but also indicate an avenue toward industrial-scale fabrication of SC-PLA products from low-crystallinity nascent powder using conventional polymer sintering equipment.
中文翻译：
立体络合物型聚乳酸新生粉的低温烧结：结晶度的影响
高分子聚l-丙交酯（PLLA）和poly（d）之间的立体复合物（SC）结晶-丙交酯（PDLA）为大幅度改善聚丙交酯（PLA）的性能提供了一条有希望的途径，但是SC型PLA（SC-PLA）的常规熔融加工几乎是不可能的，这主要是由于其差的结晶记忆效应以及SC晶体完全熔化后，具有超过220°C的高熔化温度，会导致严重的热降解。最近，我们报道了一种创新的低温（180-210°C）烧结技术，用于从新生粉末中制备SC-PLA产品。不幸的是，其实际应用受到1 GPa的极高压力的极大阻碍，必须使用该极高的压力来确保致密化粉末颗粒的良好表面润湿。考虑到这一挑战，在本文中，已经研究了粉末结晶度在低温烧结中的作用。有趣的是，我们首先证明，降低粉末的结晶度有利于在新生粉末的致密化阶段在低得多的压力下润湿颗粒，因为随着刚性晶体网络分数的降低，粉末的变形变得更加容易。此外，在随后的界面焊接阶段，更多的PLLA / PDLA链可能参与了颗粒界面之间的相互扩散和SC结晶，因此形成了大量能够紧密焊接界面的新型SC微晶。结果，通过在低至300MPa的压力下烧结，已经成功地制造了具有优异的耐热性和机械性能的SC-PLA片。全面的，
更新日期：2017-09-29
中文翻译：
立体络合物型聚乳酸新生粉的低温烧结：结晶度的影响
高分子聚l-丙交酯（PLLA）和poly（d）之间的立体复合物（SC）结晶-丙交酯（PDLA）为大幅度改善聚丙交酯（PLA）的性能提供了一条有希望的途径，但是SC型PLA（SC-PLA）的常规熔融加工几乎是不可能的，这主要是由于其差的结晶记忆效应以及SC晶体完全熔化后，具有超过220°C的高熔化温度，会导致严重的热降解。最近，我们报道了一种创新的低温（180-210°C）烧结技术，用于从新生粉末中制备SC-PLA产品。不幸的是，其实际应用受到1 GPa的极高压力的极大阻碍，必须使用该极高的压力来确保致密化粉末颗粒的良好表面润湿。考虑到这一挑战，在本文中，已经研究了粉末结晶度在低温烧结中的作用。有趣的是，我们首先证明，降低粉末的结晶度有利于在新生粉末的致密化阶段在低得多的压力下润湿颗粒，因为随着刚性晶体网络分数的降低，粉末的变形变得更加容易。此外，在随后的界面焊接阶段，更多的PLLA / PDLA链可能参与了颗粒界面之间的相互扩散和SC结晶，因此形成了大量能够紧密焊接界面的新型SC微晶。结果，通过在低至300MPa的压力下烧结，已经成功地制造了具有优异的耐热性和机械性能的SC-PLA片。全面的，
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