Anshari Raihan, Tsuboi Motohiro, Sato Harumi, Tashiro Kohji, Ozaki Yukihiro
Department of Applied Chemistry for Environment, Graduate School of Science and Technology, Kwansei Gakuin University, Gakuen-Uegahara, Sanda, Hyogo, 669-1330, Japan.
Graduate School of Human Development and Environment, Kobe University, Tsurukabuto, Nada, Kobe, 657-8501, Japan.
Sci Rep. 2025 Jan 20;15(1):2518. doi: 10.1038/s41598-025-85837-y.
Naturally weathered polypropylene (NWPP) samples are useful for investigating the effects of various degradation factors that cannot be obtained in artificial laboratory experiments. In this study, NWPP samples were extracted from beach sediments (Ashiya, Hyogo, Japan). Raman and attenuated total reflection (ATR)-Fourier-transform infrared (FTIR) spectroscopies were used to analyze variations in the composition, crystallinity, orientation, and degradation of NWPP microplastics. The degree of degradation varies from sample to sample, from position to position in a sample, and the inside surface or outside surface of a sample. Significant intensity variations were observed for Raman bands at 1150 and 842 cm⁻¹, indicating changes in the crystallinity and molecular orientation of NWPP due to degradation. The Raman spectra of the elongated pristine PP showed intensity increases at 1150, 998, and 842 cm, indicating variations in the molecular orientation of the polymer chains induced by elongation. The ATR-FTIR spectra of NWPP yield several major new features in the 3600 -3200 cm (OH stretching), 1750-1500 cm (C=O/C=C/COO stretching), and 1150-900 cm (C-O/C-C stretching) regions. Of particular note is that in the 1750-1500 cm region, at least four bands due to two kinds of vinyl groups and two kinds of carboxylate groups are clearly observed in the second derivative spectra, while bands arising from carbonyl compounds are weak. This may be the first time that the carboxylate bands have ever appeared more strongly than the carbonyl bands in the IR spectra of NWPP. The appearance of the carboxylate bands indicates two possibilities: one is the effect of seawater on the degradation of NWPP samples, and another is the oxidation of keto groups to the carboxylates. Moreover, since a few kinds of vinyl compounds and carboxylates are produced, it is very likely that the degree of degradation is high in the NWPP samples. In this way, IR spectroscopy is useful for exploring the degradation of NWPP while Raman spectroscopy is effective for examining variations in their crystallinity and orientation.
天然风化聚丙烯（NWPP）样品对于研究在人工实验室实验中无法获得的各种降解因素的影响很有用。在本研究中，NWPP样品是从海滩沉积物（日本兵库县芦屋）中提取的。利用拉曼光谱和衰减全反射（ATR）-傅里叶变换红外（FTIR）光谱来分析NWPP微塑料在组成、结晶度、取向和降解方面的变化。降解程度因样品而异，在一个样品内从一个位置到另一个位置以及样品的内表面或外表面都有所不同。在1150和842 cm⁻¹处的拉曼谱带观察到显著的强度变化，表明由于降解导致NWPP的结晶度和分子取向发生了变化。拉伸后的原始聚丙烯的拉曼光谱在1150、998和842 cm处显示强度增加，表明拉伸引起了聚合物链分子取向的变化。NWPP的ATR-FTIR光谱在3600 - 3200 cm（OH伸缩振动）、1750 - 1500 cm（C=O/C=C/COO伸缩振动）和1150 - 900 cm（C-O/C-C伸缩振动）区域产生了几个主要的新特征。特别值得注意的是，在1750 - 1500 cm区域，在二阶导数光谱中清晰地观察到至少四个由两种乙烯基和两种羧酸盐基团产生的谱带，而羰基化合物产生的谱带较弱。这可能是首次在NWPP的红外光谱中羧酸盐谱带比羰基谱带出现得更强。羧酸盐谱带的出现表明有两种可能性：一种是海水对NWPP样品降解的影响，另一种是酮基氧化为羧酸盐。此外，由于产生了几种乙烯基化合物和羧酸盐，NWPP样品的降解程度很可能很高。通过这种方式，红外光谱对于探索NWPP的降解很有用，而拉曼光谱对于检查其结晶度和取向的变化很有效。
