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A novel method and custom-made apparatus for testing the rolling tack of pressuresensitive adhesives (PSAs) and related materials were developed to measure bonding and debonding processes. The combined effects of adherend (probe) surface roughness, longitudinal load, and dwell time on bond-formation performance of ve different tacky materials chosen from various application areas were studied. These materials included synthetic PSAs (acrylic tape and the hydrocolloid dressing, Granu ex ® ), water-remoistenable adhesive (CENTRAL ® ), edible wheat our dough, and a static cling vinyl (PENSTIC ® ). Tack-rolling velocity curves were analyzed to study bonding and debondong processes. Each of the tested materials showed different tack behavior in response to varying probe roughness, external load, and velocity (dwell time). Surface wetting and mechanical interlocking were proposed as the mechanisms governing tack in most tested PSAs. Acrylic PSA tested on a smooth probe over a velocity range of 0.12-2.12 m / s showed higher tack values than on a rough one. A signi cant reduction in tack was due to restricted bond formation. Similarly, tack of Granu ex ® to a smooth model skin surface showed higher values than to a rough skin surface. CENTRAL ® showed typical cohesive failure when tested on silicone-coated paper. Interfacial failure and short-term bonding accounted for good tack performance on porous paper. Dough tested with aluminum probes showed cohesive failure similar to that of CENTRAL ® at velocities higher than 0.2 m/ s where the tack was independent of probe surface roughness. PENSTIC ® adhered only to smooth glass where the tack values tended to decrease with increased velocity. Bonding and debonding processes of the various tacky materials were clearly affected by adherend surface roughness, longitudinal load, and dwell time, and could be successfully analyzed using our novel proposed method and apparatus.

Pressure-sensitive tack is the adhesive property related to bond formation. It is a key issue when formulating hydrogel poultices for transdermal delivery, dressings, and bioelectrodes. Quantitative tack gives an indication of the potential ease and success of application when gels are brought into contact with skin. The effects of different dwell times and constant pressures on bond formation between tacky poly(vinyl alcohol) (PVA) hydrogels and a skin model were explored in the current study; these were correlated with viscoelastic properties in order to elucidate structurefunction relationships. A rolling tack test was performed using a novel apparatus capable of simultaneously controlling the pressure and dwell time in a hydrogel/skin-modelprobe system. PVA gels were formed via the freeze-thaw technique using Ca 2ϩ ions. Lower calcium availability in PVA gels resulted in longer dwell times required to complete bond formation, decreased creep compliance (at 0.01 s) and a decreased G Ј ( ϭ 40) /G Ј ( ϭ 0.01) ratio, all three leading to a loss in tack strength. All tested gels were found to have pressure-sensitive tack. The results of this study support the applicability of a rheological methodology and a novel tacktesting procedure to quantify green-bond formation in pressure-sensitive-adhesive PVA hydrogels.

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