Band 35, Heft 5

A network of poly(tetrafluoroethylene) (PTFE) microfibers in a thermoplastic polyurethane (TPU) was prepared by melt mixing the TPU with solid PTFE particles. The effect of rotor speed on the fiber dimensions was investigated. Higher shear stress was found to be the critical parameter for producing thinner PTFE fibers, rather than the shear rate imposed by the mixer. Shear stress transfer from the melt to the PTFE crystal results in solid phase plastic deformation, and the efficiency of the deformation depends on the shear stress in the matrix. All of the PTFE fiber/TPU composites show lower coefficients of friction compared with the neat TPU. The magnitude of the coefficient of friction was found to correlate with the interfacial area between PTFE and TPU generated by the microfiber network. However, for macroscale PTFE agglomerates, the reduction in the coefficient of friction is mostly affected by the uneven distribution of PTFE in the bulk and on the molded part surface.

Despite its complexity, reactive extrusion is continuously developing for the production of new and performing materials. Due to the strong coupling between flow, rheology and chemistry, optimizing this process for a given reaction remains a difficult task. Moreover, the scale-up from the laboratory to the production scale is another crucial question, which cannot be solved by conventional techniques. In this paper, we show how the use of numerical modeling may help answer these complex questions by providing realistic solutions, rapidly and without excessive costs. The example of a transesterification reaction was chosen because this reaction has been carefully characterized in previous studies. The reaction kinetics and the kinetic constants are well known and the modeling of this reactive extrusion process has proved to be realistic and accurate.

The production of bio-composites based on vulcanized rubber reinforced by natural fibers has been widely studied. However, the aging phenomenon occurring during the long-term storage generating irreversible damage is limiting the performance of this kind of composites which has not been studied in details. So the objective of this work was to characterize and understand the structure-mechanical property relationships in these bio-composites and to correlate the effective crosslinking density with physical aging as a function of fiber content (0, 20, 30 and 40 wt.%) and fiber surface modification (alkali treatment) for the system polyisoprene (PI) and coir fibers. Furthermore, interfacial adhesion was improved by using maleic anhydride grafted polyisoprene as a coupling agent. From the samples produced, a complete set of morphological (scanning electron microscopy) and mechanical (shear and tension) characterization was performed before and after natural aging. The results showed that the tensile modulus increased with fiber content for the range of conditions studied and the presence of a coupling agent always gave higher tensile strength due to better interfacial stress transfer. However, important elasticity loss (strain at break) was observed due to the low fiber elasticity. Finally, different physical aging mechanisms led to changes in the molecular configuration and a reduction of free volume caused by a post-curing phenomenon of the polyisoprene matrix and low environmental stability of the fibers. These phenomena were shown to increase the Young’s modulus of the neat matrix by eight times compared to the unaged neat polyisoprene, but a smaller variation (five times) was observed for the bio-composites which was related to different crosslinking density and coir fibers state of dispersion in the vulcanized matrix

One of the routes to minimize the environmental impact of plastics waste is the use of bio-sourced and biodegradable alternatives, particularly for packaging applications. Although Polyhydroxyalkanoates (PHA) are attractive candidates for food packaging, they have poor processability, particularly for extrusion film blowing. Thus, one relatively successful alternative has been blending PHA with a biodegradable polymer. This work proposes film blowing of a co-extruded Poly (hydroxybutyrate) (PHB) layer with a poly butylene adipateco- terephtalate (PBAT) layer to enhance bubble stability, mechanical and barrier properties. Co-extrusion is detailed, together with the different strategies followed to improve adhesion between film layers and the PHB content in the films. Films with thicknesses below 50 micron and elongation at break beyond 500% were consistently produced.

This paper presents so-called inverse rheology methods to determine various parameters that are essential to go further in terms of modelling and/or simulation in the field of polymer processing. The following systems from our previous works are presented: i) Determination of the molecular structure of a poly(e-caprolactone) polymerized in-situ by ring-opening; ii) Measurement of the mutual diffusion coefficient: two cases are considered, namely the diffusion of a plasticizer and the diffusion of an organic peroxide in a polymer melt and iii) Determination of the average length of polymer nanofibers in suspension and study of the universal behavior of nanofibers of different natures in dilute and semi-dilute suspensions. The application of these different studies in the field of reactive extrusion, blending and multi-scale structuring are presented and discussed.

Blends of polycaprolactone (PCL) and poly(3-hydroxyoctanoate) P(3HO) were prepared by melt compounding. These immiscible blends exhibited droplet-matrix morphology at compositions up to 30 wt% P(3HO). Even though the addition of amorphous P(3HO) decreased the crystallinity of PCL, the crystallization temperature of the blends increased by 6 to 7 8C. Blends containing up to 30 wt% P(3HO) had higher crystallization rates, and lower crystallization half-times compared to neat PCL. The viscosity of PCL decreased upon addition of P(3HO), making the blends suitable for processing using a 3D bioplotter. Compositions with 10 to 30 wt% P(3HO) were ideal for processing, because of their improved crystallization kinetics, reduced stickiness and good flow properties. Estimation of the interfacial tension by fitting the Palierne model to the linear viscoelastic properties of the blends revealed good compatibility, which gave rise to synergistic effects in the thermal and mechanical properties. The fibres prepared by 3D bioplotting maintained droplet matrix morphology, with finer particle size than the original compounded material. In addition to favourable viscosity and thermal properties, the extruded fibres containing 30 wt% P(3HO) had comparable modulus to the neat PCL, while exhibiting good ductility. These blends may be suitable alternatives to PCL for biomedical applications, because they provide a range of crystallinities, crystallization rates and viscosities.

A comprehensive numerical model is developed for the simulation of the laser-assisted automated tape placement process of carbon fiber/thermoplastic composites. After being heated with a laser, the thermoplastic is welded with the help of a consolidation roller onto a substrate made up of layers of tapes bonded onto one another. Under the pressure applied by the roller, the thermoplastic flows and the tape reaches its final thickness. The numerical model is developed in three sequential steps that can be used to identify the required pressure and temperature distribution to achieve a good bond. Firstly, a heat transfer simulation is performed to determine the temperature distribution into the incoming tape under the consolidation roller. Secondly, a rheological model is developed to examine the polymer flow under the roller and to obtain the pressure field. Finally, the consolidation level between the substrate and the tape is investigated through the degree of intimate contact, which is related to the processing parameters such as the roller velocity, the laser power density and the compaction force.

This work focuses on fabrication of multi-hollow polyimide gel and aerogel particles from a surfactant-free oil-in-oil emulsion system using a microfluidic droplet generator operating under dripping mode. The multi-hollow gel and aerogel particles have strong potential in thermal insulation. Under jetting and tip-streaming regime of microfluidic flows, droplets are generated with no occluded liquid phase. The present study investigates a means of designing polyimide gel particles with plurality of internal liquid droplets by strategically manipulating the flow rates of the continuous and dispersed phase liquids through the microfluidic droplet generator. The multi-hollow polyimide aerogel particles obtained after supercritical drying of the gel particles present mesopores, high BET surface area, and excellent prospect for thermal insulation.

This work describes the effect of reduced graphene oxide (RGO) addition in natural rubber (NR). Firstly, RGO was synthesized based on the improved Hummer’s method then characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) to confirm that the RGO surface contains hydroxyl, epoxy, and carboxyl functional groups to improve graphene interaction with the NR matrix. In a second step, the synthesized RGO was predispersed in NR latex using the co-coagulation technique then added at different amounts (0 to 2 parts per hundred rubber (phr)) to a basic NR formulation and compounded in an internal mixer. The results show that the crosslink density of the developed NR/RGO nanocomposites increased by 65% for RGO concentration of 2.0 phr. For the same RGO concentration, a significant increase in tensile strength (53%) and Young’s modulus (31%) were also observed. Finally, a significant improvement (26%) of the thermal conductivity was obtained with the addition of only 0.5 phr of RGO.

Understanding of polypropylene (PP) foaming is critically important to reduce the weight of automotive parts. In this study, we used a batch foaming simulation system with visualization cell, to observe the foaming behaviors of PP that is blown with CO 2 and N 2 under various experimental conditions. We found that the nucleating agent content, initial temperature, pressure (i. e., gas content), and pressure drop rate during foaming have a significant effect on cell nucleation and cell growth. The cell density and the void fraction of PP foamed with CO 2 and N 2 , respectively, were separately observed and compared. It was found that under the same experimental conditions, the maximum cell density of PP foamed with CO 2 was higher than that of PP foamed with N 2 . However, the maximum cell density of PP foamed with CO 2 was determined to be lower than that of PP foamed with N 2 , when the same gas mole numbers were employed. Based on the experimental results, optimum foaming conditions and effective processing strategies for PP-CO 2 system are suggested.