Advanced spectroscopy, microscopy, diffraction and thermal analysis of polyamide adhesives and prediction of their functional properties with solid-state NMR spectroscopy†
Abstract
Adhesives are an essential class of industrial polymers with applications ranging from pressure-sensitive adhesives to hot-melt adhesives used for repairing conveyor belts in mines. The composition and homogeneity of a polyamide-based hot-melt adhesive (HMA) was revealed with attenuated total reflection (ATR)-FTIR and solid-state NMR spectroscopy. Analysis of the polyamide shows that it is obtained through sustainable manufacturing based on dimer acids. ATR-FTIR showed incorporation of an abrasion-resistant additive on the surface of the HMA but was unsuitable for other additives such as carbon black or an antistatic agent. Quantitative 13C NMR spectroscopy revealed heterogeneity in the distribution of an antistatic agent in the HMA, which was supported by observations with differential scanning calorimetry (DSC). 1H NMR relaxation and two-dimensional wideline separation (2D-WISE) NMR revealed differences in the molecular dynamics of functional groups in the polyamide resin and the additives dispersed in the resin matrix. 1H T2 relaxation revealed that the molecular mobility of the least mobile and moderately mobile components increased with increasing temperature and antistatic agent content. 2D-WISE NMR revealed a phase separation in the base resin matrix and plasticization of the whole sample at very high antistatic agent content. 1H T2 relaxation showed possible correlations with mechanical properties such as Young's modulus and Shore A hardness and weaker correlations with adhesive properties such as T-peel strength. This shows the suitability of NMR to assist product innovation through the design of better-performing HMAs or of HMAs for application in different climatic conditions.
- This article is part of the themed collection: Polymer Chemistry Pioneering Investigators 2021