Mechanism confirmation of organofunctional silanes modified sodium silicate/polyurethane composites for remarkably enhanced mechanical properties.

Hybrid reinforced sodium silicate/polyurethane (SS/PU) composites mainly derived from low-cost SS and polyisocyanate are produced by a one-step method based on the addition of 3-chloropropyltrimethoxysilane (CTS). The wettability of SS on PU substrate surface is much improved as CTS content increases from 0.0 to 3.5 wt%. Furthermore, with 2.5 wt% of CTS optimal addition, the fracture surface morphology and elemental composition of the resulting SS/PU composites are characterized, as well as mechanical properties, chemical structure and thermal properties. The results indicate that the CTS forms multiple physical and chemical interactions with the SS/PU composites to induce an optimized organic-inorganic hybrid network structure thus achieving simultaneous improvement of compressive strength, flexural strength, flexural modulus and fracture toughness of the SS/PU composites, with the improvement of 12.9%, 6.6%, 17.5% and 9.7%, respectively. Moreover, a reasonable mechanism explanation for CTS modified SS/PU composites is confirmed. Additionally, the high interface areas of the organic-inorganic phase and the active crosslinking effect of the CTS are the main factors to determine the curing process of the SS/PU composites.

Effect of Silane Treatment on Mechanical Properties of Polyurethane/Mesoscopic Fly Ash Composites.

In view of the accidents such as rock mass breakage, roof fall and coal slide in coal mines, polyurethane/mesoscopic fly ash (PU/MFA) reinforcement materials were produced from polymethylene polyphenylene isocyanate (PAPI), the polyether polyol, flame retardant, and MFA using stannous octanate as a catalyst. 3-Glycidoxypropyltrimethoxysilane (GPTMS) was grafted on MFA surface, aiming to improve the mechanical properties of PU/MFA composites. The analyses of infrared spectroscopy and compression resistance reveal that the GPTMS can be successfully attached to the surface of MFA, and the optimum modification dosage of GPTMS to MFA is 2.5 wt % (weight percent). On this basis, the effect of GPTMS on the mechanical properties of PU/MFA reinforcement materials during the curing process was systematically investigated through a compression test, a fracture toughness test, a three-point bending test, a bond property test, and a dynamic mechanics analysis. The results show that the compression property, fracture toughness, maximum flexural strength, and bond strength of PU/MFA composites increase by 21.6%, 10.1%, 8.8%, and 19.3%, respectively, compared with the values before the modification. Furthermore, the analyses of scanning electron microscope and dynamic mechanics suggest that the coupling agent GPTMS can successfully improve the mechanical properties of PU/MFA composites because it eliminates the stress concentration and exerts a positive effect on the crosslink density and hardness of PU/MFA composites.