Plastics,Rubber and Composites: Macromolecular Engineering

This paper aims to increase the through-plane thermal conductivity of polymer composites by adjusting the filler orientation. Two methods were tested: a combination of immiscible polymers (PP-PET) and adding a foaming agent to a PA6-based composite. In both cases, graphite was used as a thermal conductive filler. Compounds with 10, 20 and 30 wt-% graphite were made for both methods. The through-plane thermal conductivity increased for all PA6- foaming agent composites, while the in-plane thermal conductivity decreased compared to PA6 without foaming agent. PP-PET combinations generally outperformed the PP in through-plane performances as well. Tensile strength decreased with increasing amounts of graphite. As expected, adding foaming agents and a second phase decreased strength as well compared with virgin materials. With further optimisation, a combination of fillers and foaming agents in thermoplastics or two-phase systems could prove to be valuable in thermal management applications.

The reinforcement of recycled polypropylene (rPP) with mineral fillers, to obtain modulus values of 3000–4000 MPa has proven challenging for recyclers, whereas this is common practice for virgin PP. The main difference between recycled and virgin PP is the contaminating presence of other polymers. In this study, the composition of rPP sourced from electrical and electronic waste was analytically estimated. The rPP was found to be a PP/HDPE blend with ca. 90/10 m% ratio. Furthermore, the effect of HDPE on the thermal and physical properties of talc-filled PP was investigated by means of re-engineered blends and talc-filled compounds. It was found that HDPE has a profound effect on the degree to which rPP can be reinforced by talc. However, the quantified effects of the HDPE alone were not of sufficient magnitude to account for the full difference in properties between talc-filled rPP and virgin PP.

To extend the diversity of commercial materials relevant for fused filament fabrication (FFF), the relation of nozzle temperature and layer thickness with respect to final product mechanical performance is examined for the less studied group of (co)polyesters, considering tensile and impact strength and microscopic imaging. It is demonstrated that with limited polymer degradation, one can focus on increasing the layer height (from 0.1 to 0.3 mm) by tuning of the contribution of inter-layer welding, whereas with significant degradation, a lower layer height (0.1 mm) is needed to exploit the contribution of intra-layer welding for which a higher nozzle temperature (e.g. 260°C) is beneficial. The relevance of degradation is studied by both melt flow index and rheological analysis. The study ultimately provides the best FFF parameters for three commercial copolyesters and highlights the competition of inter- and intra-welding as a key microscopic material design strategy.

In classical viscoelastic theory, phase difference between loading and viscoelastic solid response does not change if loading frequency remains constant. In our experiments, however, it was found that phase difference was gradually decreased as the number of stress cycles was increased. Using local weighted linear regression algorithm (LWLRA), experimental data were successfully analysed and phase difference values between loading and response were obtained. The relation between initial phase difference and loading frequency obeys power-law. Based on Maxwell viscoelastic model, the relationship between relaxation time and loading frequency was proposed, which could be described by a power function.

In order to ensure structural integrity in such applications of composites materials, it is important to understand the material behaviour under mechanical loadings and predict correctly its responses. In this paper, the authors perform several three-point bending tests on a typical stacking sequences used in composite structures. Inspection techniques involving a digital microscope are used to study the successive failures and the effect of the thickness ratio (l h⁻¹) on nonlinear behaviour. It was found that successive failures depend on the stacking sequence where the orthogonal sequences have a significant effect on the delamination between the plies. To describe the nonlinear behaviour observed, Von-Karman's large deflection theory and classical plate theory (CPT) are employed in the formulation of analytical modelling used in this work. The Riccati equation obtained leads to predict the experimental nonlinear curves with good accuracy. However, a slight dispersion between the experimental and analytical curves less than 11% was observed at large deflection.

High performance rigid polyurethane foam (RPUF) has been designed by using hyperbranched polyurethane (HBPU) polyol with high functionality to replace traditional polyol. The influences of different types of polyol on the apparent density and heat deformation temperature of RPUF were studied. The microstructures, including cell structure, cell diameter and distribution, were characterised by SEM. Effects of polyol types on the cell structure of RPUF were discussed. Thermal resistance and thermal stability were measured by the thermal deformation vicat temperature meter and TGA. Thermal conductivity of RPUF was characterised by Hot Disk, and the mechanical properties were also measured. Compared with the RPUFs obtained from commercial polyether polyols, RPUF-HBPU exhibited enhanced thermal resistance. Besides, the compressive strength, flexural strength and tensile strength were up to 4.5, 4 and 3.5 times, respectively, than that of traditional RPUF as well. The as-prepared RPUF-HBPU displayed low thermal conductivity/thermal diffusion and good thermal stability.