We investigated a new method for estimating the amount of silanes physisorbed on a silica particle surface treated with silane coupling agents from a weight loss curve measured by thermogravimetric (TG) analysis. The silica particles were treated with 3-glycidoxypropyl trimethoxysilane (GPTMS) or 3-mercaptopropyl trimethoxysilane (MrPTMS) with both dry and wet treatment methods. In the TG curve for silica particles treated with GPTMS, the weight decreased in three steps: 100-1708C (first step), 170-2508C (second step), and 250-4008C (third step). The weight loss in the first step decreased with heating or acetone washing to remove the physisorbed molecules as the posttreatment. The three weight losses were found to be based on physisorbed monomeric silanes (first step), physisorbed polycondensed silanes (second step), and chemisorbed silanes (third step), respectively. The amount of physisorbed silanes on the silane-treated layer could be estimated from the TG curve without solvent washing to remove the physisorbed molecules. The amounts obtained were almost equal to those measured from a comparison of the weight losses for the treated particles before and after acetone washing. A similar tendency was observed for MrPTMS-treated silica. Thus, the amount of physisorbed silanes in silane-coupling-agent-treated silica particles was successfully estimated from the TG measurements. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43256.

The stringiness of crosslinked polyacrylic pressure-sensitive adhesives (PSA) was observed during 90 peeling under a constant peel rate with various adherends in order to clarify the influence of interfacial adhesion on the stringiness behavior. The crosslinked random copolymer of butyl acrylate with 5 wt % acrylic acid was used as a representative PSA. Poly(methyl methacrylate) (PMMA), polycarbonate (PC), poly(vinyl chloride) (PVC), fused quartz plates and some surface-modified poly(ethylene terephthalate) films were used as adherends. The films were pasted on a glass plate using a cyanoacrylate adhesive. The 180 peel strength was higher in the order of PVC >> PMMA % PC > other adherends. All observed stringiness was sawtooth-shaped, but the stringiness width and length were longer in the same order. The number of sub-branches formed at the tips of the strings was much more for the PVC, PMMA and PC adherends. Frames formed at the front end of the strings in the case of PVC adherend. Sufficient interfacial adhesion generates large internal deformation of the PSA layer. Internal deformation occurred preferentially over peeling as a result of front frame formation. The string length and the peel load required for the constant peel rate have good correlation with the peel strength. The estimation of generated inner stress in the fibrils of the strings was possible by analysis using the string length for various adherends and the stress-strain curve of pure PSA.

The stringiness of crosslinked polyacrylic pressure-sensitive adhesive (PSA) was observed during 90 peeling under the constant peel load. The random copolymer of butyl acrylate with 5 wt % acrylic acid crosslinked by N,N,N 0 ,N 0 -tetraglycidyl-m-xylenediamine was used as PSA. All observed stringiness upon peeling was sawtooth-shaped, but it could be classified into three types dependent on the degree of crosslinking. The typical sawtooth-shaped stringiness with interfacial failure was observed at the relatively higher crosslinker content ranging from 0.008 to 0.016 chemical equivalents (Eq.), where the PSA has high cohesive strength and low interfacial adhesion. The frame formed at the front end of stringiness at the content ranging from 0.002 to 0.004 Eq. Sufficient interfacial adhesion and deformability generate large internal deformation of the PSA layer. Internal deformation occurred preferentially over peeling as a result of front frame formation. The mode of peeling was changed from cohesive failure to interfacial failure in this range of crosslinker content. The sawtooth-shaped with cohesive failure was observed at the lower content ranging from 0 to 0.001 Eq. The PSA has high interfacial adhesion and low cohesive strength, and thus exhibited cohesive failure. The PSA after peeling remained in the shape of belts. It was found that the shape of stringiness is strongly dependent on the balance between the interfacial adhesion and the cohesive strength of PSA. When the sawtooth-shaped stringiness with frame formed, the peeling rate was lowest. This means the peel strength should be the maximum in this shape of stringiness. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40336.

No abstract

Effect of adhesive thickness on the wetting and deformation behaviors during probe tack test of pressure-sensitive adhesive (PSA) was investigated. For this purpose, cross-linked poly(n-butyl acrylate-acrylic acid) [P(BA-AA)] and poly(2-ethylhexyl acrylate-acrylic acid) [P(2EHA-AA)] random copolymers with an acrylic acid content of 5 wt % and thicknesses in the range of $15-60 lm were used. Tack was measured using the probe tack test and the fracture energy was calculated from the areas under force-displacement curve recorded during debonding process. From contact time dependence of fracture energy, the rising rate of fracture energy with contact time increased with increasing of adhesive thickness and was P(2EHA-AA) > P(BA-AA). The fracture energy was P(BA-AA) > P(2EHA-AA) at shorter contact time, whereas it reversed at longer contact time. This was caused by two different interfacial adhesions: the physical wetting of PSA molecules to the adherend surface with contact time and the chemical interaction between the acrylic acid units and the adherend surface. From the force-displacement curve measured under the condition of sufficient interfacial adhesion, both maximum force and displacement-namely, the deformability of PSA during debonding process-increased with adhesive thickness. The degree of increase of deformability was P(2EHA-AA) > P(BA-AA). The fracture energy was found to depend on the development of interfacial adhesion during contacting process and the deformability of PSA during debonding process.