A both multiscale and multi-techniques approach was developed to characterize the thermal aging in air at 70, 90, 100 and 120 °C of High Tenacity Polyvinyl Alcohol (HT-PVAl) yarns, and to elucidate the consequences of thermal aging on the chemical structure, crystalline morphology and several physico-chemical and mechanical properties of practical interest. First of all, FTIR and UV–Vis spectrometries showed that the main degradation products are isolated (1656 cm⁻¹) and conjugated (1592 cm⁻¹) carbon-carbon double bonds, and a large variety of carbonyl products such as: esters (1757 cm⁻¹), aldehydes (1737 cm⁻¹), carboxylic acids (1720 cm⁻¹), ketones (1707 cm⁻¹), but also polyenones (1630 cm⁻¹). Possible mechanistic schemes were then proposed to explain the formation of all these different degradation products. Moreover, no change in the physico-chemical properties of the amorphous phase was detected by modulated differential scanning calorimetry and dynamic vapor sorption. In contrast, the decrease in both melting temperature and crystallinity ratio with exposure time clearly indicates a “nibbling” of the crystalline phase during thermal aging, thus highlighting a chemical attack preferentially localized at the amorphous/crystal interface for this complex anisotropic material. This heterogeneous degradation is responsible for the loss of fracture properties in tension of HT-PVAl yarns. Fairly simple relationships between the structural variables determined at the different scales of analysis were established. As an example, a linear correlation was found between the changes in fracture properties and the changes in crystalline morphology.

开发了一种多尺度和多种技术的方法来表征高强度聚乙烯醇（HT-PVAl）纱线在70、90、100和120°C下在空气中的热老化，并阐明热老化对化学药品的影响具有实际意义的结构，晶体形态和几种物理化学和机械性能。首先，FTIR和UV-Vis光谱表明，主要的降解产物是分离的（1656 cm ^-1）和共轭的（1592 cm ^-1）碳-碳双键，以及各种羰基产物，例如：酯（ 1757 cm ^-1），醛（1737 cm ^-1），羧酸（1720 cm ^-1），酮（1707 cm ^-1），还有聚烯（1630 cm ^-1）。然后提出了可能的机理方案来解释所有这些不同降解产物的形成。此外，通过调制差示扫描量热法和动态蒸气吸附未检测到非晶相的物理化学性质的变化。相反，熔融温度和结晶度随暴露时间的降低明显表明在热老化过程中晶相“咬蚀”，从而突出了对于这种复杂的各向异性材料而言，化学侵蚀优先位于非晶/晶体界面。这种异质降解是造成HT-PVAl纱线张力断裂性能下降的原因。建立了在不同分析规模下确定的结构变量之间的简单关系。举个例子，