Antunes Ana, Popelka Anton, Aljarod Omar, Hassan Mohammad K, Kasak Peter, Luyt Adriaan S
Center for Advanced Materials, Qatar University, P.O. Box 2713 Doha, Qatar.
Polymers (Basel). 2020 Aug 5;12(8):1743. doi: 10.3390/polym12081743.
The effect of accelerated weathering on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV-based nanocomposites with rutile titanium (IV) dioxide (PHBV/TiO) was investigated. The accelerated weathering test applied consecutive steps of UV irradiation (at 340 nm and 0.76 W m irradiance) and moisture at 50 °C following the ASTM D4329 standard for up to 2000 h of exposure time. The morphology, chemical structure, crystallization, as well as the mechanical and thermal properties were studied. Samples were characterized after 500, 1000, and 2000 h of exposure time. Different degradation mechanisms were proposed to occur during the weathering exposure and were confirmed based on the experimental data. The PHBV surface revealed cracks and increasing roughness with the increasing exposure time, whereas the PHBV/TiO nanocomposites showed surface changes only after 2000 h of accelerated weathering. The degradation of neat PHBV under moisture and UV exposure occurred preferentially in the amorphous phase. In contrast, the presence of TiO in the nanocomposites retarded this process, but the degradation would occur simultaneously in both the amorphous and crystalline segments of the polymer after long exposure times. The thermal stability, as well as the temperature and rate of crystallization, decreased in the absence of TiO. TiO not only provided UV protection, but also restricted the physical mobility of the polymer chains, acting as a nucleating agent during the crystallization process. It also slowed down the decrease in mechanical properties. The mechanical properties were shown to gradually decrease for the PHBV/TiO nanocomposites, whereas a sharp drop was observed for the neat PHBV after an accelerated weathering exposure. Atomic force microscopy (AFM), using the amplitude modulation-frequency modulation (AM-FM) tool, also confirmed the mechanical changes in the surface area of the PHBV and PHBV/TiO samples after accelerated weathering exposure. The changes in the physical and chemical properties of PHBV/TiO confirm the barrier activity of TiO for weathering attack and its retardation of the degradation process.
研究了加速老化对聚（3-羟基丁酸酯-co-3-羟基戊酸酯）（PHBV）以及含金红石型二氧化钛（PHBV/TiO₂）的PHBV基纳米复合材料的影响。加速老化试验按照ASTM D4329标准，依次进行紫外线照射（波长340 nm，辐照度0.76 W/m²）和50℃的潮湿环境处理，暴露时间长达2000小时。研究了其形态、化学结构、结晶情况以及力学和热性能。在暴露500、1000和2000小时后对样品进行表征。提出了在老化暴露过程中发生的不同降解机制，并根据实验数据得到证实。随着暴露时间增加，PHBV表面出现裂纹且粗糙度增加，而PHBV/TiO₂纳米复合材料仅在加速老化2000小时后才出现表面变化。纯PHBV在潮湿和紫外线暴露下的降解优先发生在非晶相中。相比之下，纳米复合材料中TiO₂的存在阻碍了这一过程，但长时间暴露后，聚合物的非晶区和结晶区都会同时发生降解。在没有TiO₂的情况下，热稳定性以及结晶温度和结晶速率都会降低。TiO₂不仅提供紫外线防护，还限制了聚合物链的物理移动性，在结晶过程中起到成核剂的作用。它还减缓了力学性能的下降。PHBV/TiO₂纳米复合材料的力学性能逐渐下降，而纯PHBV在加速老化暴露后则出现急剧下降。使用调幅 - 调频（AM - FM）工具的原子力显微镜（AFM）也证实了加速老化暴露后PHBV和PHBV/TiO₂样品表面积的力学变化。PHBV/TiO₂物理和化学性质的变化证实了TiO₂对老化侵蚀的阻隔活性及其对降解过程的延缓作用。
