Characterisation of tack for uni-directional prepreg tape employing a continuous application-and-peel test method

Abstract

Employing a test method with coupled application and peel phases, tack was characterised for a UD prepreg tape. Different aspects of tack were explored by varying test parameters and material condition. In addition, different surface combinations were studied. In general, the test parameters, feed rate and temperature, affect the balance between cohesion within the resin and adhesion between resin and substrate. Exploring a range of parameters is required to understand the effect of viscoelastic resin properties on tack. The application pressure determines the true contact area between prepreg and substrate and hence affects tack. Changes in molecular mobility in the resin related to specimen conditioning, i.e. ageing or moisture uptake, result in maximum tack to occur at lower or higher feed rates, respectively. Differences in tack for different material combinations can be attributed to different molecular interactions at the contact interfaces and different resin distributions on the prepreg surfaces.

Prepreg tack: A review of mechanisms, measurement, and manufacturing implication

“…This has led to the suggestion that the time‐temperature superposition principle (TTS) may be applicable toward prepreg tack which has been confirmed repeatedly for peel testing in subsequent studies. [ 21,86–88 ] Here, dynamic prepreg stiffness was found to increase monotonically as a function of feed rate while bell‐shaped curves are determined experimentally for tack. The rate dependency of tack, for example, for PSA, has traditionally been explained based on viscoelastic behavior exhibited by polymers during the debonding process.…”

“…The results are supported by several studies utilizing different test methods. [ 16,88,104,105 ] Hence, the influence seems to be independent of the measurement technique. Figure 6 evidently showcases that a lack of tack due to insufficient compaction force can be countervailed by an increase in dwell time.…”

“…The influence of the compaction roller (stiff vs compliant roller) on prepreg tack was also studied. [ 88 ] Differences in tack were observed and attributed to differences in pressure distribution and contact time between both rollers. The actual deformation behavior of the investigated rollers remained unknown in the study.…”

“…These studies yield a common result: Whenever tack between two prepreg layers was determined and compared to other material combinations, tack was found to be highest for the prepreg‐prepreg combination. Endruweit et al [ 88 ] report the adhesive performance of the prepreg‐prepreg combination to be 2.5 to 5.5 higher than for prepreg‐steel depending on the face. No effective tack toward fluorinated ethylene propylene representing the surface coating of the compaction roller was detected.…”

“…The shift of maximum tack as a consequence of progressive material ageing was also substantiated by results from TTS for peel testing (see Section 4.3.1 for details) performed in ref. [88]. It was deduced from these studies that a certain flowability is necessary for surface wetting and, consequently, for a considerable tack to be measured.…”