Rheology of SiO2/(Acrylic Polymer/Epoxy) Suspensions. I. Linear Viscoelasticity

Linear viscoelastic properties of SiO2/(AP/EP) suspension with various SiO2 volume fractions (φ) in a blend of acrylic polymer (AP) and epoxy (EP) were investigated at various temperatures (T). The AP/EP contained 70 vol% of EP. The SiO2 particles were treated with epoxy silane coupling agent. The effects of the SiO2 particles are more pronounced in the terminal zone: a transition from viscoelastic liquid (φ ≤ 30 vol %) to viscoelastic solid (φ ≥ 40 vol %) was observed which can be interpreted as a critical gelation occurring at a critical particle content and critical gel temperature. The SiO2/(AP/EP) systems exhibited a critical gel behavior at φ ≅ 35 vol % and T ≅ 100 °C characterized with a power-law relationship between the storage and loss moduli (G′ and G″) and frequency (ω); G′ = G″/tan(nπ/2) ∝ ωn. The critical gel exponent (n) was estimated to be about 0.45. The gelation occurred with increasing T

The effect of 1,3:2,4-bis-O-(p-methlbenzylbenzylidene)-D-sorbitol(PDTS) on uniaxial elongational viscosity of polypropylene

We investigated the dynamic viscoelasticity and elongational viscosity of polypropylene (PP) containing 0.5wt% of 1,3:2,4-bis-O-(p-methylbenzylidene)-D-sorbitol (PDTS). The PP/PDTS system exhibited a sol-gel transition (Tgel) at 193 °C. The critical exponent n was nearly equal to 2/3, in agreement with the value predicted by a percolation theory. This critical gel is due to a three-dimensional network structure of PDTS crystals. The elongational viscosity behavior of neat PP followed the linear viscosity growth function 3η+(t), where η+(t) is the shear stress growth function in the linear viscoelastic region. The elongational viscosity of the PP/PDTS system also followed the 3η+(t) above Tgel, but did not follow the 3η+(t) and exhibited strong strain-softening behavior below Tgel. This strain-softening can be attributed to breakage of the network structure of PDTS with a critical stress (σc) of about 104 Pa