Developing effective recycling pathways for polyolefin waste, enabling a move to a circular economy, is an imperative that must be met. Postuse modification has shown promising results in upcycling polyolefins, removing the limitation of inertness, and improving the final physical properties of the recycled material while extending its useful lifetime. Grafting of maleic anhydride groups to polypropylene is an established industrial process that enhances its reactivity and provides a convenient route to further functionalization and upcycling. In this work, maleic anhydride grafted polypropylene was hydroxylated and subsequently cured with a diisocyanate to form a thermoset polyurethane (PU). The crystal structure (unit cell and lamellar structure) of the polypropylene (PP) was preserved in the PU. At room temperature, the PU showed a high modulus due to the crystallization behavior of the PP; upon increasing the temperature above the melting temperature, the modulus decreased to a rubbery plateau, consistent with formation of a network. The resulting PU showed a higher glass transition temperature and lower degree of crystallinity than its PP predecessor due to the crosslinked nature of the polymer. The mechanical integrity of the PU was maintained through several reprocessing cycles due to the melt processability enabled by the presence of a urethane exchange catalyst. This functionalization and upcycling route thus offers a promising alternative to repurposing PP waste in which the creation of melt-processable thermoset polymers expands applications for the materials.

中文翻译：

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聚丙烯向热固性聚氨酯的功能化和再利用


为聚烯烃废料开发有效的回收途径，实现向循环经济的转变，是必须满足的当务之急。使用后改性在升级回收聚烯烃、消除惰性限制、改善回收材料的最终物理性能同时延长其使用寿命方面显示出可喜的成果。马来酸酐基团接枝到聚丙烯是一种成熟的工业工艺，可增强其反应性，并为进一步功能化和升级回收提供便捷的途径。在这项工作中，马来酸酐接枝的聚丙烯被羟基化，随后用二异氰酸酯固化，形成热固性聚氨酯 （PU）。聚丙烯 （PP） 的晶体结构（晶胞和层状结构）保留在 PU 中。在室温下，由于 PP 的结晶行为，PU 显示出高模量;当温度升高到熔化温度以上时，模量降低到橡胶状平台，与网络的形成一致。由于聚合物的交联性质，所得 PU 显示出比其前身 PP 更高的玻璃化转变温度和更低的结晶度。由于氨基甲酸乙酯交换催化剂的存在实现了熔融加工性，因此在几个后处理周期中保持了 PU 的机械完整性。因此，这种功能化和升级再造路线为重新利用 PP 废料提供了一种很有前途的替代方案，其中创造可熔融加工的热固性聚合物扩大了材料的应用。