Mariko Sasaki

Relation between phase structure and peel adhesion of poly(styrene-isoprene-styrene) triblock copolymer/tackifier blend system

The effect of tackifier on the adhesive properties of a model pressure-sensitive adhesive tape was investigated. For this purpose, a model system consisting of poly(styrene-isoprene-styrene) triblock copolymer as the base polymer and a typical aliphatic petroleum resin as the tackifier was prepared. The tackifier content ranged from 10 to 60 wt%. The tackifier used has a good compatibility with polyisoprene, whereas it has a poor compatibility with polystyrene. The 180° peel adhesion was measured. The peel adhesion increased with the tackifier content, while the degree of increase became more significant above 40 wt%. The pressure sensitivity appeared obviously and the maximum peel adhesion was obtained without heating above 40 wt%. The phase structure was determined using pulse 1H-NMR, transmission electron microscopy and dynamic mechanical analysis. A phase structure in which spherical polystyrene domains with a mean size of about 20 nm were dispersed in the polyisoprene continuous phase was observed. It was found that the tackifier-rich phase of the order of nanometers in size was formed in the polyisoprene matrix and the concentration increased with the tackifier content. The tackifier-rich phase seemed to develop the cohesive strength and, thus, it increased the peel adhesion.

Surface Analysis of Silane Nanolayer on Silica Particles Using 1H Pulse NMR

The surface treatment of spherical silica particles with silane coupling agent having mercapto group was carried out and structure and amount of silane nanolayer formed on silica surface were analyzed using 1H pulse nuclear magnetic resonance (NMR) and thermogravimetric analysis, respectively. Effects of loading amount and number of alkoxy groups of silane on the structure were investigated. Silanes with dialkoxy and trialkoxy structures were used as silane coupling agents and the loading amount of the silane on the silica surface was varied from one to nine times the amount required for monolayer coverage. The relaxation time was longer in the dialkoxy type than in the trialkoxy type of silane. The relaxation time increased with increase of the loading amount of silane for the dialkoxy type; on the other hand, there was no influence of the loading amount of silane for the trialkoxy type. It was found that the silane structure was flexible for the dialkoxy type, whereas it was rigid for the trialkoxy type. Effect of mixing ratio of silane coupling agents having di- and trialkoxy groups on the silane nanolayer structure was also investigated, and 1H pulse NMR studies confirmed that the relaxation time measured for the mixed silane-treated system was between those for the dialkoxy and the trialkoxy structures and depended on the mixing ratio. It was found that the network density of silane-treated layer on silica particles could be controlled by varying the molar ratio of dialkoxy/trialkoxy silane coupling agents.

Effects of Compatibility of Acrylic Block Copolymer and Tackifier on Phase Structure and Peel Adhesion of Their Blend

The effect of compatibility of polymer and tackifier on the adhesion properties of pressure-sensitive adhesive tape was investigated. For this purpose, a model pressure-sensitive adhesive tape was prepared. A mixture of poly(methyl methacrylate)-block-poly(butyl acrylate)-block-poly(methyl methacrylate) triblock copolymer and a similar diblock copolymer was used as the base polymer. And three kinds of tackifiers, namely a rosin phenolic resin (A), a special rosin ester resin (B) and a hydrogenated cycloaliphatic resin (C) were used. The compatibility with the base polymer was in the order of tackifier A > B > C. Transmission electron microscopy studies confirmed that the tackifier A had good compatibility, where agglomerates of the tackifier with a size of about 10 nm only were observed. Larger and distinct agglomerates of tackifier were observed for tackifier B and the size increased with the tackifier content. The tackifier C formed domains with a mean size of several tens μm. Dynamic mechanical analysis indicated that both the glass transition temperature and modulus increased at low temperature and the modulus at high temperature decreased by the addition of tackifier for tackifiers A and B. This tendency was more remarkable for tackifier A as compared to tackifier B. An increase of the glass transition temperature was never observed for tackifier C. The peel adhesion was in the order of tackifier A > B > C. It was found that the compatibility of tackifier and base polymer had strong effect on adhesion properties.

Adhesion properties of polyurethane pressure-sensitive adhesive

In this study, the adhesion properties of polyurethane (PUR) pressure-sensitive adhesive (PSA) were investigated. The PUR-PSA was prepared by the cross-linking reaction of a urethane polymer consisting of toluene-2,4-diisocyanate and poly(propylene glycol) components using polyisocyanate as a cross-linking agent. The peel strength increased with the cross-linking agent content and exhibited cohesive failure until the maximum value, after which it decreased with interfacial failure. The PUR-PSA exhibited frequency dependence of the storage modulus obtained from dynamic viscoelastic measurements, but did not show dependence of the tack on the rolling rate measured using a rolling cylinder tack test under the experimental conditions used, which is quite different from the acrylic block copolymer/tackifier system. The PUR-PSA showed strong contact time dependence of tack measured by a probe tack test. The tendency was significantly larger than for the acrylic block copolymer/tackifier system. Therefore, the storage modulus increased, whereas the interfacial adhesion seems to be decreased with increase in the rolling rate for this PUR-PSA system. It was estimated that the influence of rolling rate on the interfacial adhesion and the storage modulus was offset, and, as a result, the rolling cylinder tack did not exhibit rate dependency.

Tensile properties of styrene-butadiene rubber/silica composites with mercapto functional silane coupling agents: influences of loading method and alkoxy group number

The influences of alkoxy group number and loading method of silane coupling agents on the mechanical properties of a styrene-butadiene rubber/silica composite were investigated. Mercapto functional silane coupling agents with dialkoxy and trialkoxy structures were used. The pre-treatment method and the integral blend method were compared. Both the fracture stress and modulus at 200% strain were higher in the pre-treatment than in the integral blend for dialkoxy type composites. However, they were higher in the integral blend than in the pre-treatment for trialkoxy-type composites. The interaction between the silane chains on the silica surface and the rubber molecular chains at the interfacial region was estimated by 1H pulse nuclear magnetic resonance spectroscopy using an unvulcanized silica/rubber mixture. It was found that the binding of rubber molecular chains by the silane chains was higher in the pre-treatment system for dialkoxy-type composites, whereas it was higher in the integral blend for trialkoxy-type composites. The reason is proposed as follows: in the pre-treatment for dialkoxy type, a linear silane chain formed in the case of multi-layer coverage. The silane chain entangled with the rubber chain in the interfacial region and improved the reinforcement effect. For the trialkoxy type, a network structure formed using the pre-treatment method, lowering the amount of entanglement. However, in the integral blend for trialkoxy type, the formation of the silane network and the entanglement progressed simultaneously during the preparation process. A well-entangled interfacial region was formed.

Influences of the alkoxy group number and treatment condition on the structure of glycidoxy functional silane-treated layer on silica particles analyzed by 1H pulse NMR

The surface treatment of spherical silica particles using a silane coupling agent with a glycidoxy group was conducted and the effect of the alkoxy group number on the molecular mobility of the silane chain was investigated by 1H pulse nuclear magnetic resonance (NMR). Silanes with di-alkoxy and tri-alkoxy structures were used, and the silica particles were treated with 2-propanol solution and heated at 120 °C for 24 h after solvent evaporation. The surface coverage of the silica surface was in the range from two to three layers. For multilayer coverage, linear chain and network structures were expected to form on the surface by polycondensation reaction using the di- and tri-alkoxy structures, respectively. However, the relaxation times for silane chains with both di- and tri-alkoxy structures measured by pulse NMR were short, which indicates that both silane chains formed rigid network structures. Fourier transform infrared spectroscopic analysis revealed that ring opening of the epoxy group occurred, followed by reaction to form the network structure, even with the di-alkoxy structure. Ring opening of the epoxy group could be reduced by setting the heating temperature at 80 °C. There was a significant difference in flexibility between the silane-layers with di- and tri-alkoxy structures after heating at 80 °C, as reflected by the relaxation time.

Effects of Polystyrene Block Content on Morphology and Adhesion Property of Polystyrene Block Copolymer

Effects of polystyrene block content on adhesion property and phase structure of polystyrene block copolymers were investigated. Polystyrene-block-polyisoprene-block-polystyrene triblock and polystyrene-block-polyisoprene diblock copolymers with different polystyrene block contents in the range from 13 to 35 wt% were used. In the case of the low polystyrene block content (below 16 wt%), a sea-island structure was observed: near-spherical polystyrene domains having a mean diameter of about 20 nm were dispersed in polyisoprene matrix. The phase structure changed from a sea-island structure to a cylindrical structure with an increase of polystyrene block content (over 18 wt%). Peel strength decreased with an increase of polystyrene block content and the pure triblock copolymers had lower peel strength than their blends with the diblock copolymers. Pulse nuclear magnetic resonance studies indicated that molecular mobility of polyisoprene phase decreased with an increase of polystyrene block content, and the molecular mobility was lower in the pure triblock than in the blend. Thus, the peel strength was found to be related to molecular mobility. The adhesion strength of the block copolymer depended on the molecular mobility: high molecular mobility can promote interfacial adhesion.

Structure of silane layer formed on silica particle surfaces by treatment with silane coupling agents having various functional groups

The surface treatment of spherical silica particles with silane coupling agents having various organic functional groups was conducted and the effect of the alkoxy group number on the molecular flexibility of the silane chain with multilayer coverage was investigated using 1H-pulse nuclear magnetic resonance spectroscopy. The silica particles were treated with 2-propanol solution and heated at 120 °C for 24 h after solvent evaporation to accelerate the polycondensation reaction of silanol groups. For multilayer coverage, flexible linear chain and rigid network structures were expected to form on the surface from the di- and trialkoxy structures, respectively. However, the rigid network structure was formed from both the di- and trialkoxy structures with glycidoxy, amino, and methacryloxy functional silanes. Ring opening of the epoxy group occurred, followed by reaction to form the network structure, even with the dialkoxy structure of the glycidoxy functionality. Ring opening of the epoxy group could be reduced by pH adjustment of the treatment solution and the linear chain structure was formed from the dialkoxy structure. In the case of amino and methacryloxy functional groups, hydrogen bonds were formed between the amino or methacryloxy groups and the silanol groups on the silica surface or silane molecules.

Temperature dependence of tack and pulse NMR analysis of polystyrene block copolymer/tackifier system

The influence of tackifier structure on the temperature dependence of tack for a polystyrene block copolymer/tackifier system was investigated. A blend of polystyrene-block-polyisoprene-block- polystyrene triblock and polystyrene-block-polyisoprene diblock copolymers was used as the base polymer. Four different tackifiers were used: special rosin ester resin (RE), rosin phenolic resin (RP), hydrogenated cyclo-aliphatic resin (HC), and aliphatic petroleum resin (C5). Tack at 20 °C increased with the tackifier content for both RE and HC tackifier systems. Tack is affected by two factors: the work of adhesion at the adherend interface and the viscoelastic properties of the adhesive. The good balance of these two factors brought high tack. The adhesive with 10 wt.% tackifier exhibited the highest tack at 20 °C, whereas those with 30 and 50 wt.% tackifier were lower than those systems with 10 wt.% of the RP or C5 tackifiers. The adhesive with overly high hardness lowered the work of adhesion and the tack was not improved with more than 30 wt.%. A compatibility test in toluene solution and in solid state showed that tackifier RE has good compatibility with both polyisoprene and polystyrene, whereas tackifier RP has lower compatibility. Tackifiers HC and C5 had good compatibility with polyisoprene, but poor compatibility with polystyrene, and that of C5 was poorer. Pulse nuclear magnetic resonance (NMR) analyses indicated that tackifiers RE and HC effectively restrict the molecular mobility of polyisoprene phase.

1H pulse NMR analysis of silane-treated layers on glass fiber surfaces

The surface treatment of a glass fiber using mercapto-functional silane coupling agent having a di- or trialkoxy group has been studied. The surface of silane-treated fiber is observed by scanning electron microscopy. The treated layer looks hard like glass for the trialkoxy silane-treated, whereas it looks soft for the dialkoxy silane-treated. Molecular mobility of the treated layer is analyzed by 1H pulse nuclear magnetic resonance spectroscopy. The amount of silane loading increases with increased silane concentration in the treatment solution. The relaxation time for the surface layer is longer for the dialkoxy structure than for the trialkoxy structure. The silane chain is flexible in the dialkoxy structure, but is rigid for the trialkoxy structure, independent of the loading amount of silane. The relaxation behavior for the mixture of the di- and trialkoxy structures is between those of the pure dialkoxy and trialkoxy structures and depends on the mixing ratio. The network density of silane chains on the glass fiber can be controlled by varying the mixing ratio of the di- and trialkoxy compounds.