The influence of filler types and content on the curing behavior and properties of a bio-based polyurethane engineered sealant

Polyurethane (PU) sealants are widely used in practical projects to fill road cracks, extend road life and increase the strength of construction joints. And the fillers not only reinforce the sealant, but also effectively reduce costs. In this paper, a series of experiments were carried out to investigate the effects of filler types and contents on the curing behavior and properties of a novel bio-based PU sealant. Firstly, the optimum filler type was determined by fluorescence microscopy (FM) test and physical properties test. The dispersion of different fillers of different contents in the sealant and its effect on the mechanical properties were determined. Secondly, the effect of fillers on the curing behavior was investigated using Fourier transform infrared spectroscopy (FTIR), gel time experiment and surface drying time experiment. The cross-section surface micro-morphologies of the specimens after tensile tests were analyzed by scanning electron microscopy (SEM). Finally, the viscoelasticity and low-temperature properties were determined using dynamic mechanical analysis (DMA). The high-temperature properties of sealant were investigated using thermogravimetric (TG) analysis. The results showed that precipitated calcium carbonate (PCC) was the best filler. Moreover, fumed silica (FS), as a reactive filler, significantly influences the performance of the sealant. With the increase of filler content, the mechanical and high temperature properties of the sealant were enhanced. And the curing process was accelerated. But the low-temperature performance was reduced. Besides, excessive amount of PCC was worse to its uniform dispersion in the sealant and lead to defections in the materials, reducing the strength of the sealant. The optimum PCC content was recommended to be 10 wt%.