Thermoplastic | EPFL Graph Search

A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains associate by intermolecular forces, which weaken rapidly with increased temperature, yielding a viscous liquid. In this state, thermoplastics may be reshaped and are typically used to produce parts by various polymer processing techniques such as injection molding, compression molding, calendering, and extrusion. Thermoplastics differ from thermosetting polymers (or "thermosets"), which form irreversible chemical bonds during the curing process. Thermosets do not melt when heated, but typically decompose and do not reform upon cooling. Above its glass transition temperature and below its melting point, the physical properties of a thermoplastic change drastically without an associated phase change. Some thermoplastics do not fully crystallize below

Hybrid Processing of Thermoplastic Based Multimaterials

Rajasundar Chandran

There is a growing interest in exploring novel material combinations and processing technology to manufacture complex 3D shaped polymer and composite structures. In the field of prosthetics and orthotics, this need is significant with additional challenges of providing patient specific customization to these devices in a cost-effective manner. Thermoplastic based materials(TP) including thermoplastic elastomers (TPE) and their composite counterparts have the potential to address these applications. The objectives of the research are to develop composite preforms that can conform to complex 3D structures, understand the processing phenomena in particular the fusion bonding mechanisms of different thermoplastic materials forming hard and soft interfaces and finally develop processing strategies that are suitable for the manufacture of complex 3D structures with these multimaterials. A novel TPE based composite preform consisting of continuous glass fibres was first manufactured by a continuous melt impregnation technique, extremely well suited for the studied TPE material. This process resulted in superior fibre wetting and impregnation characteristics for the composite preform. Furthermore, TPE reinforced by glass fibres provided preforms which can conform easily to 3D shapes owing to the flexible nature of the matrix. Then isothermal integration of polypropylene based glass fibre (iPPGF) composites with the TPE materials was studied and the bond strengths of bilayer specimens under different processing conditions were determined. The bonding temperature and pressure were tuned to promote the best fusion bonding conditions which was verified from peel tests and microscopic characterization of the interfaces. Further improvements in bond strength and fusion bonding time was achieved by non-isothermal fusion bonding techniques namely overmolding and 3D printing. The processing windows were then obtained for these two processes under a wide range of fusion bonding conditions and for various TPE and TP based materials. The presence of a continuous plasticized iPP phase in the TPE was determined to play an important role in the bonding through the establishment of intimate contact and interdiffusion mechanisms during the molding process. The influence of the interface temperature and bonding pressure was shown to govern the wetting and intimate contact of the interfaces and to compensate shrinkage respectively. The established processing conditions permitted tailoring of the bond strengths for TPE-iPP and TPE-iPPGF interfaces. These results can be directly applied for high volume manufacture of complex 3D shaped composite parts. The effects of the TPE composition (fillers, reinforcements, TP content, surface roughnessâŠ) and of bonding temperature, pressure and time, were thus better understood under the non-isothermal bonding conditions encountered in the additive processes. The results of the FDM printing can be combined with other low pressure processing techniques such as thermoforming to manufacture hybrid multimaterials 3D structures. The research is applied in developing a hybrid processing technology which proposes the combination of thermoplastic-based multimaterials and different processing techniques that are suitable for the manufacture of the next generation of composite applications in particular for customized affordable prosthetic limbs.

EPFL2017

A life cycle analysis of novel lightweight composite processes: Reducing the environmental footprint of automotive structures

Baris Çaglar, Colin Gomez, Véronique Michaud, Christian Rytka, Vincent Werlen

In this study, three novel thermoplastic impregnation processes were analyzed towards automotive applications. The first process is thermoplastic compression resin transfer molding in which a glass fiber mat is impregnated in through thickness by a thermoplastic polymer. The second process is a melt-thermoplastic Resin Transfer Molding (RTM) process in which the glass fibers are impregnated in plane with the help of a spacer. The third process, stamp forming of hybrid bicomponent fibers, coats the fibers individually during the glass fiber production. The coated fibers are used to produce a fabric, which is then further processed by stamp forming. These three processes were compared in a life cycle analysis (LCA) against conventional resin compression resin transfer molding with either glass or carbon fibers and metal processes with either steel or aluminum that can be new, partly or fully recycled using the case study of the production, life and disposal of a car bonnet. The presented LCA includes the main phases of the process: extraction and preparation of the raw materials, production and preparation of the mold, process, and energy losses. To include the life of the analyzed bonnet, the amount of diesel that is used to drive the weight of the bonnet for 300 ' 000 km is calculated. In this LCA, the disposal of the bonnet is integrated by analyzing the used energy for the recycling and the incineration. The results show the potential of the developed thermoplastic impregnation processes producing automobile parts, as the used energy producing a thermoplastic bonnet is in the same range as the steel production.

ELSEVIER SCI LTD2022

Novel tooling for direct melt impregnation of textile with variotherm injection moulding: Methodology and proof of concept

Véronique Michaud, Christian Rytka, Vincent Werlen

Thermoplastic compression resin transfer moulding coupled with injection moulding is an appealing process for the production of thermoplastic composites. However, its implementation at an industrial scale remains challenging as variotherm injection moulding could prevent solid skin formation in the parting line, making cavity sealing difficult. In this study, a tool for thermoplastic compression resin transfer moulding and the related methods and process parameters for an implementation at an industrial scale are presented. The validity of the concept is proved by producing and characterizing composite plates with elevated fibre volume fractions and advantageous mechanical properties at a range of production temperatures within a cycle time not exceeding 20 min. The best mechanical properties were obtained at a production temperature of 270 degrees C with a bending strength of 477 MPa, a flexural modulus measured at 25.7 GPa and a fibre volume content of 67%.

SAGE PUBLICATIONS LTD2022

Hybrid Processing of Thermoplastic Based Multimaterials

Rajasundar Chandran

EPFL2017