Yoshida Koh, Teramoto Sayaka, Gong Jin, Kobayashi Yutaka, Ito Hiroshi
Department of Organic Materials Science, Graduate School of Organic Materials Science, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510, Yamagata, Japan.
Aquaculture Division, Iwate Fisheries Technology Center, 3-75-3 Heita, Kamaishi 026-0001, Iwate, Japan.
Polymers (Basel). 2024 Jun 27;16(13):1830. doi: 10.3390/polym16131830.
Microplastics' spreading in the ocean is currently causing significant damage to organisms and ecosystems around the world. To address this oceanic issue, there is a current focus on marine degradable plastics. Polycaprolactone (PCL) is a marine degradable plastic that is attracting attention. To further improve the biodegradability of PCL, we selected a completely new protein that has not been used before as a functional filler to incorporate it into PCL, aiming to develop an environmentally friendly biocomposite material. This novel protein is derived from the mucus bubbles of the violet sea snail (VSS, Janthina globosa), which is a strong bio-derived material that is 100% degradable in the sea environment by microorganisms. Two types of PCL/bubble composites, PCL/b1 and PCL/b5, were prepared with mass ratios of PCL to bubble powder of 99:1 and 95:5, respectively. We investigated the thermal properties, mechanical properties, biodegradability, surface structure, and crystal structure of the developed PCL/bubble composites. The maximum biochemical oxygen demand (BOD) degradation for PCL/b5 reached 96%, 1.74 times that of pure PCL (≈55%), clearly indicating that the addition of protein fillers significantly enhanced the biodegradability of PCL. The surface morphology observation results through scanning electron microscopy (SEM) definitely confirmed the occurrence of degradation, and it was found that PCL/b5 underwent more significant degradation compared to pure PCL. The water contact angle measurement results exhibited that all sheets were hydrophobic (water contact angle > 90°) before the BOD test and showed the changes in surface structure after the BOD test due to the newly generated indentations on the surface, which led to an increase in surface toughness and, consequently, an increase in surface hydrophobility. A crystal structure analysis by wide-angle X-ray scattering (WAXS) discovered that the amorphous regions were decomposed first during the BOD test, and more amorphous regions were decomposed in PCL/b5 than in PCL, owing to the addition of the bubble protein fillers from the VSS. The differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA) results suggested that the addition of mucus bubble protein fillers had only a slight impact on the thermal properties of PCL. In terms of mechanical properties, compared to pure PCL, the mucus-bubble-filler-added composites PCL/b1 and PCL/b5 exhibited slightly decreased values. Although the biodegradability of PCL was significantly improved by adding the protein fillers from mucus bubbles of the VSS, enhancing the mechanical properties at the same time poses the next challenging issue.
微塑料在海洋中的扩散目前正在对世界各地的生物和生态系统造成重大破坏。为了解决这一海洋问题，目前人们将重点放在了海洋可降解塑料上。聚己内酯（PCL）是一种备受关注的海洋可降解塑料。为了进一步提高PCL的生物降解性，我们选择了一种以前从未使用过的全新蛋白质作为功能性填料，并将其掺入PCL中，旨在开发一种环保型生物复合材料。这种新型蛋白质源自紫螺（VSS，球形泡螺）的黏液泡，它是一种强大的生物衍生材料，在海洋环境中可被微生物100%降解。制备了两种PCL/泡复合材料，PCL/b1和PCL/b5，PCL与泡粉的质量比分别为99:1和95:5。我们研究了所开发的PCL/泡复合材料的热性能、力学性能、生物降解性、表面结构和晶体结构。PCL/b5的最大生化需氧量（BOD）降解率达到96%，是纯PCL（≈55%）的1.74倍，这清楚地表明添加蛋白质填料显著提高了PCL的生物降解性。通过扫描电子显微镜（SEM）进行的表面形态观察结果明确证实了降解的发生，并且发现PCL/b5与纯PCL相比经历了更显著的降解。水接触角测量结果表明，在BOD测试之前所有片材都是疏水的（水接触角>90°），并且在BOD测试后由于表面上新产生的凹痕而显示出表面结构的变化，这导致表面韧性增加，进而表面疏水性增加。通过广角X射线散射（WAXS）进行的晶体结构分析发现，在BOD测试期间非晶区域首先分解，并且由于添加了来自VSS的泡蛋白填料，PCL/b5中分解的非晶区域比PCL中的更多。差示扫描量热仪（DSC）和热重分析（TGA）结果表明，添加黏液泡蛋白填料对PCL的热性能只有轻微影响。在力学性能方面，与纯PCL相比，添加黏液泡填料的复合材料PCL/b1和PCL/b5的值略有下降。虽然通过添加来自VSS黏液泡的蛋白质填料显著提高了PCL的生物降解性，但同时提高力学性能是下一个具有挑战性的问题。
