Enzymatic Functionalization of HMLS-Polyethylene Terephthalate Fabrics Improves the Adhesion to Rubber

Among synthetic thermoplastic fiber materials for reinforcement, high modulus and low shrinkage poly(ethylene terephthalate) (HMLS-PET) became the major carcass material for the low- to medium-end tire segment. Usually cords are coated with a resorcinol-formaldehyde-latex (RFL) dip to achieve acceptable power transmission. However, the low concentration of polar groups on the PET's surface requires an additional activation with costly and potentially toxic chemicals to create additional nucleophilic groups prior to RFL dipping. Here, a green enzyme based alternative to chemical HMLS-PET activation was investigated. Four different cutinase variants from Thermobifida cellulosilytica were shown to hydrolyze HMLS-PET cords, creating new carboxylic and hydroxyl groups with distinct exoendo-wise selectivity. The highest degree of enzymatic functionalization reached a concentration of 0.51 nmol mm-2of COOH with a release of 1.35 mM of soluble products after 72 h. The chemical treatment with 1 M NaOH released more soluble products leading up to a 10% decrease of the tensile strength while the functionalization degree achieved was only 0.21 nmol mm-2. This clearly indicates a more endowise mode of hydrolysis for the enzymatic treatment when compared to chemical hydrolysis. Scanning electron microscopy of the fibers confirmed the aggressiveness of the chemical treatment, whereas the enzymatic approach only led to 0.7% solubilization of the polymer with no loss of mechanical properties and crystallinity changes. The newly created groups were chemically accessible and reactive in the dipping step and led after the vulcanization to a significant improvement of the adhesion between the polymer and a representative carcass rubber compound according to the peel tests.