New type of primers based on polypropylene grafted maleic anhydride (PP-g-MAH) –strength analysis

Primers are an appealing approach for enhancing adhesion to low-energy surfaces owing to their cost-effectiveness in manufacturing and operation, high efficiency, and scalability. Commercial adhesion coatings typically contain 3-20% chlorinated polyolefins, which are environmentally unstable and contribute to the overall cost. This study proposes primers based on polypropylene grafted with maleic anhydride (PP-g-MAH) as a novel alternative. The research investigates the strength of adhesive joints formed using a PP-g-MAH-based primer. Polypropylene substrates coated with the primer were bonded to polyethylene foam coated with acrylic adhesive. The study examines various factors, including concentration of PP-g-MAH in the primer solution, the degree of grafting of polypropylene with maleic anhydride, the solvent type, the temperature of primer application, and pressure duration and magnitude. Peel strength analysis demonstrates that PP-g-MAH primers significantly enhance the adhesion of polypropylene substrates to the acrylic adhesive on the adhesive tape, requiring only a 1% solution to achieve maximum joint strength (averaging 35.53 N and 37.29 N at 0.5% and 1% concentrations, respectively). Moreover, peel strength decreases with increasing polypropylene modification with maleic anhydride (41.1 N for 0.66% grafting, 31.1 N for 1.0%, and 29.7 N for 1.43%). High-temperature application is necessary, with peak strength observed at 100 °C (54.4% increase compared to 25 °C) and 120 °C (57.9%). However, solvent selection can influence primer application temperature, with decalin and toluene yielding the highest strength (averaging 45.2 N and 42.8 N) compared to tetrachloroethane and xylene (37.3 N and 35.5 N). Pressure application is crucial for bonding polymers with foam adhesive tape, significantly enhancing strength (e.g., 71% increase at 20 bar) with short-duration pressure (42.9 N for 10 seconds, 33.5 N for 60 seconds).