For the first time, a new flame-retardant formula based on dimethyl methylphosphonate (DMMP), aluminum hydroxide (ATH), ammonium polyphosphate (APP), and expandable graphite (EG) was applied to polyisocyanurate–polyurethane foams and found to exhibit a high flame-retardant efficiency and low cost, to be environmentally friendly, and to allow for the reduction of the amount of solid flame retardants added. The multiple effects were evaluated based on thermal conductivity tests, compressive strength tests, limiting oxygen index (LOI) measurements, cone calorimetry tests, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that ATH can form “villi”-like substances during the combustion process. In the presence of ATH and APP, dense spherical substances were produced. When EG was added to the system, a wormlike carbon layer that adsorbed phosphate-containing acid resulting from APP decomposition was formed during the decomposition process, so that the carbon layer was denser. The combined effects of the villi-like and spherical substances as well as the wormlike carbon layer can block heat and flame propagation from being transferred to the unburned foam.

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ABSTRACT:The dynamic viscoelastic properties of poly(vinyl alcohol) (PVA)/H 2 O solutions with concentrations of 10 to 25 wt % have been characterized by controlled-stress rheometry at 30 C. Parameters relating to the linear and nonlinear viscoelasticities include complex viscosity (g*), storage modulus (G 0 ), loss tangent (tan d), relaxation time (k), thixotropy, and creep. Change curves of g*, G 0 , tand, and k with frequency (x) have been obtained for the PVA/H 2 O solutions. Creep and recovery testing yielded compliance (J 0 ) curves with loading and unloading. Shear stress versus rate profiles of the PVA solutions have been obtained through thixotropic measurements. The PVA concentration has been found to have a profound influence on the rheological properties of the aqueous solutions. Four aqueous solutions of 10, 15, 20, and 25 wt % PVA at 30 C exhibited shear-thinning and showed different transition behaviors of g* and G 0 with frequency, and different degrees of creep under constant stress to recovery with time. The 10 wt % PVA solution was viscous and displayed the lowest g* and G 0 ; the 25 wt % PVA solution was viscoelastic and displayed the highest g* and G 0 ; the 15 and 20 wt % PVA solutions showed g* and G 0 values and creep to recovery behaviors intermediate between those of the 10 wt % and 25 wt % PVA solutions. The different rheological properties of these PVA/H 2 O solutions are considered to correlate with interchain hydrogen bonds and shearinduced orientation in the solutions. Shearing is able to break the intrachain and interchain hydrogen bonds, and, at the same time, the orientation creates new interchain hydrogen bonding. The reorganization of hydrogen-bonding mode contributes to the transitions of the macroscopic viscoelasticity with frequency.

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