Methods and process parameters of gel coating on laminated composites - A review

In the past two decades the use of laminated polymer composites for the marine and aerospace applications has been increased remarkably. These are continuously exposed to aggressive environmental conditions which lead to moisture absorption, strength degradation and delamination of the composite. The main issue with these composites is their non-biodegradability, which may cause environmental hazards after their disposal. In the recent days this problem has been effectively addressed by natural fibers with their biodegradable property. The hydrophilic property of natural fibers results into moisture uptake leading to weak interfacial bonding between fiber and polymer matrix. Moisture absorption is the major culprit which will reduce the favourable properties of these natural composites. Gel coating is one among the best available methods to overcome this problem. Evolution of gel coating was with the aim of aestheticization of the laminate, but as on date it has become a proven method for the improvement of mechanical performance, chemical resistance and wear resistance also. Gel coats are widely used to provide exterior protection for the finished part of fiber reinforced composite material. Gel coat can be applied with various thicknesses to the composite, but it is necessary to maintain the thickness at the critical stress points. Also the interface between the gel coat and laminate composite decides the mechanical performance of the composite. The performance of the gel coated laminate is highly prone to the method of coating and its process parameters. This review article mainly focuses on the gel coating methods and process parameters. A review has been documented with a particular emphasis on the natural fiber composites.