Main Priyanka, Petersmann Sandra, Wild Nadine, Feuchter Michael, Duretek Ivica, Edeleva Mariya, Ragaert Peter, Cardon Ludwig, Lucyshyn Thomas
Polymer Processing, Montanuniversitaet Leoben, Otto-Gloeckel-Straße 2, 8700 Leoben, Austria.
Faculty of Engineering and Architecture, Centre for Polymer and Material Technologies, Ghent University, Technologiepark Zwijnaarde 130 (Zone C3), 9052 Zwijnaarde, Belgium.
Polymers (Basel). 2023 Oct 18;15(20):4126. doi: 10.3390/polym15204126.
Biobased plastics have the potential to be sustainable, but to explore their circularity further, current end-of-life options need to be broadened. Mechanical recycling is one of the most accepted methods to bring back plastics into the loop. Polyhydroxybutyrates (PHBs) are biobased and biodegradable in nature with promising properties and varied applications in the market. This study focuses on their potential for mechanical recycling by multiple extrusion cycles (E1-E5) and multi-faceted characterization of the virgin (V) and reprocessed materials from E1 to E5. The behavior is compared to polypropylene (PP) as a reference with a similar property profile, which has also been reprocessed five times. The thermal properties of both series showed a stable melting point and thermal decomposition temperature from thermal analyses (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)). However, a steady increase in the degree of crystallinity was observed which could counterbalance the decrease in molecular weight due to repeated extrusion measured by gel permeation chromatography and resulted in similar values of tensile strength across the cycles. The strain at break was impacted after the first extrusion, but no significant change was observed thereafter; the same was observed for impact strength. Even in scanning electron microscopy (SEM) images, virgin and E5 samples appeared similar, showing the stability of morphological characteristics. Fourier transform infrared spectroscopy (FTIR) results revealed that no new groups are being formed even on repeated processing. The deviation between the PHB and PP series was more predominant in the melt mass flow rate (MFR) and rheology studies. There was a drastic drop in the MFR values in PHB from virgin to E5, whereas not much difference was observed for PP throughout the cycles. This observation was corroborated by frequency sweeps conducted with the parallel plate method. The viscosity dropped from virgin to E1 and E2, but from E3 to E5 it presented similar values. This was in contrast to PP, where all the samples from virgin to E5 had the same values of viscosity. This paper highlights the possibilities of mechanical recycling of PHB and explains why future work with the addition of virgin material and other additives is an area to be explored.
生物基塑料具有可持续发展的潜力，但为了进一步探索其循环利用性，当前的报废处理选择需要拓宽。机械回收是使塑料重回循环利用的最被认可的方法之一。聚羟基丁酸酯（PHB）本质上是生物基且可生物降解的，具有良好的性能且在市场上有多种应用。本研究聚焦于通过多次挤出循环（E1 - E5）对其进行机械回收的潜力，以及对原始（V）材料和从E1到E5的再加工材料进行多方面表征。将该行为与具有相似性能特征的聚丙烯（PP）作为参考进行比较，PP也经过了五次再加工。通过热分析（差示扫描量热法（DSC）和热重分析（TGA）），两个系列的热性能均显示出稳定的熔点和热分解温度。然而，观察到结晶度稳步增加，这可以抵消通过凝胶渗透色谱法测量的由于重复挤出导致的分子量下降，并在整个循环中产生相似的拉伸强度值。断裂伸长率在第一次挤出后受到影响，但此后未观察到显著变化；冲击强度也有同样的情况。即使在扫描电子显微镜（SEM）图像中，原始样品和E5样品看起来也相似，显示出形态特征的稳定性。傅里叶变换红外光谱（FTIR）结果表明，即使经过反复加工也没有形成新的基团。在熔体质量流动速率（MFR）和流变学研究中，PHB和PP系列之间的偏差更为明显。从原始PHB到E5，MFR值急剧下降，而PP在整个循环中未观察到太大差异。通过平行板法进行的频率扫描证实了这一观察结果。粘度从原始样品到E1和E2下降，但从E3到E5呈现相似的值。这与PP形成对比，PP从原始样品到E5的所有样品粘度值都相同。本文强调了PHB机械回收的可能性，并解释了为什么未来添加原始材料和其他添加剂的工作是一个有待探索的领域。
