A novel strategy of implementing coupling agents in micro/nano-fibrillated composites

Abstract

Applying a coupling agent (CA) is one of the most commonly used methods to improve the dispersion and interfacial adhesion in filler reinforced composites. However, for micro/nano-fibrillated composites which contain high aspect ratio polymeric micro/nano-sized fibrils, the extra coupling agent has negative effects on the fibril formation. The coupling agent actively prevents the coalescence of the dispersed droplets into fibrils. Also, due to its low viscosity, it will migrate, resulting in Marangoni stress and a lubrication effect weakening the deformation of droplets. An alternative method is proposed in this paper; instead of one-step dosing of a high content of maleic anhydride-graft-polypropylene (MA-g-PP) coupling agent before polypropylene/polyethylene terephthalate (PP/PET) fibrillation, it is separated into two steps. An initial amount of CA 1% is applied before fibrillation aiming only to decrease the spherical phase. A second complementary dose of CA is applied during isotropization to improve the adhesion between the new matrix and the micro/nano-fibrils and, eventually, to improve the dispersion of the fibrils, without impairing the fibril morphology. The relationship between CA and micro/nano-fibrillation is derived to identify the optimal CA content. The effect of CA on the rheological and crystallization properties are examined. Then, the conventional and proposed two-step CA fibrillated composites are compared. The mechanical properties of the proposed fibrillated composites show higher tensile strength (37.8 MPa) and tensile modulus (2.0 GPa) than both the conventional CA fibrillated and the non-CA fibrillated composites.