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.

This work investigates the linear and non-linear viscoelastic melt rheology of four grades of polycarbonate melt compounded with 3 wt% Nanocyl NC7000 multiwalled carbon nanotubes and of the matching matrix polymers. Amplitude sweeps reveal an earlier onset of nonlinearity and a strain overshoot in the nanocomposites. Mastercurves are constructed from isothermal frequency sweeps using vertical and horizontal shifting. Although all nanocomposites exhibit a second plateau at ∼10 5 Pa, the relaxation times estimated from the peak in loss tangent are not statistically different from those of pure melts estimated from cross-over frequencies: all relaxation timescales scale with molar mass in the same way, evidence that the relaxation of the polymer network is the dominant mechanism in both filled and unfilled materials. Non-linear rheology is also measured in large amplitude oscillatory shear. A comparison of the responses from frequency and amplitude sweep experiments reveals the importance of strain and temperature history on the response of such nanocomposites.

A single-stage peel method was employed to determine the relationship between key processing parameters and tack for a standard aerospace carbon/epoxy prepreg subjected to various levels of room-temperature out-time. The temperature-dependent viscoelasticity of the resin was studied using parallel plate rheometry and modelled using a simple Arrhenius equation. Differential scanning calorimetry and gel permeation chromatography results showed that, over a period of 35 days under ambient conditions, resin Tg increased, while no significant change in polymer chain length was observed. Time-temperature superposition was applied to construct tack master curves for each out-time interval, which were shown to approximately coincide when considering shift factors attributed to changes in Tg. Process maps considering prepreg out-time were generated using tack master curves to inform process parameters and achieve desirable tack levels. This type of tailored process control is anticipated to improve resource utilization when manufacturing large preforms which take several days to complete.

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. ABSTRACTThis work investigates the effects of primary compounding temperature and secondary melt processes on the mechanical response and electrical resistivity of polycarbonate filled with 3 wt% multi-walled carbon nanotubes (CNT). Nanocomposites were melt compounded in an industrial setting at a range of temperatures, and subsequently either injection moulded or compression moulded to produce specimens for the measurement of electrical resistivity, surface hardness, and uniaxial tensile properties. Secondary melt processing was found to be the dominant process in determining the final properties. The effects observed have been attributed to structural arrangements of the CNT network as suggested by morphological evidence of optical microscopy and resistivity measurements. Properties were found to be relatively insensitive to compounding temperature. The measured elastic moduli were consistent with existing micromechanical models.

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