How to achieve a release of free CNTs from degrading composite materials

W. Wohlleben, S. Hirth, M.W. Meier
BASF SE, DE

Keywords: lifecycle, CNT composites, weathering degradation, mechanical degradation, structure-property relationship

Summary:

We performed specific studies to understand the combined action of chemical matrix degradation (by both wet and dry weathering) and afterwards mechanical stress. By weathering, protruding networks of CNTs can remain after photochemical degradation of the matrix, but to what extent does this induces a release of free CNTs ? Starting from an unrealistic worst case (ultrasound on weathered composites), we scale the shear forces and derive release probabilities in units of mg CNT released /m² polymer/year. To date, no release of free CNTs has been reported unless the polymer matrix is chemically degraded. In this field we add a detailed case study for purely mechanical degradation, to understand the interesting transition from nanocomposites whose fragments completely embed CNTs to some other nano-composites whose fragments show protrusions of individual CNTs on their surface. Other aspects, such as the chemical lysis route or the thermal decomposition route, are not backed up with new data here, but are included in our final views on emerging structure-property-relationships that indicate a high or low probability of release.