https://popups.uliege.be/esaform21/index.php?id=86 Coordinator: Prof. Vincent Sobotka Co-organisers: Dr. Nadine Allanic, Dr. Olivier De Almeida, Prof Abderrahim Maazouz, Prof. Gary Menary, Prof. Fabrice Schmidt, Dr. Roberto Spina, Dr. Peter Martin Description: The aim of this symposium is to bring together specialists from academia and industry dealing with modelling and experimental analysis of polymer processing and induced properties. This MS extends from thermo-chemo-mechanical characterization of polymers to coupled transfers in processes, in particular heat transfer in molded parts, tools and interfaces. The main topics of the mini symposium are: Thermomechanical modelling and optimization of polymers processes. New challenges for characterization and modelling of thermo-chemo-physical properties in homogeneous and heterogeneous media; Heat transfer phenomena in molds/tools associated with polymers processes; Specific thermal metrology applied to polymers processing. Mini Symposia fr Wed, 03 Mar 2021 09:36:41 +0100 Sun, 30 May 2021 09:28:46 +0200 https://popups.uliege.be/esaform21/index.php?id=86 0 https://popups.uliege.be/esaform21/index.php?id=409 Thermoplastic composites offer new manufacturing prospects, thanks to the ability to melt the matrix. Welding, tape placement, 3D printing, overmoulding, or even stamping involve adhesion of the thermoplastic polymer at high temperature. First, under heat and pressure, contact at the microscopic scale is ensured by the deformation of surface roughness, this is the intimate contact step. Then, the development of the mechanical strength of the assembly is controlled by the diffusion of macromolecules at the interface which is defined as the healing step. Nowadays, continuous manufacturing processes tend to be faster and present very short residence time which could limit the adhesion development. A good understanding of these mechanisms is therefore very important to control and predict such industrial processes. Welding tests at different temperatures and contact pressures were carried out over a large range of residence times using a controlled welding bench enabling very short welding times (down to 1 second). The mechanical adhesion between PEKK-carbon composite samples was characterized using double cantilever beam fracture tests. Adhesion was found to develop in two steps which could be described as an intimate contact-healing coupled step and a pure healing step. From this, the healing kinetics was identified and an empirical model was developed to account for the effect of pressure on adhesion build-up. This model could then be compared with existing models to describe the establishment of intimate contact between the coupons. Fri, 19 Mar 2021 18:40:55 +0100 https://popups.uliege.be/esaform21/index.php?id=409 https://popups.uliege.be/esaform21/index.php?id=737 This paper deals with polyisobutylene (PIB) migration through post-consumer agricultural waste multilayer films based on four linear low-density polyethylene (LLDPE) matrices. Connections between shear, elongational rheology and tack surface properties were revealed for both model and recycled blends. The effects of aging time and temperature were investigated and rationalized, depending on the short- and long-chain branching in LLDPE matrices as well their polyethylene (PE) crystallization. Linear and nonlinear viscoelastic properties were influenced by even small amounts of PIB. This migration also influenced slippage in the steady-flow regime. Transient uniaxial extensional properties were shown to be very sensitive to the presence of PIB, which seems to hold back the PE strain hardening properties. Therefore, the axial force and the surface friction coefficient were determined and discussed in correlation with bulk rheological findings. These results help unveil new insights about the physical mechanisms governing PIB migration with or without fillers inhibiting this migration in recycled films. Sun, 21 Mar 2021 11:43:39 +0100 https://popups.uliege.be/esaform21/index.php?id=737 https://popups.uliege.be/esaform21/index.php?id=748 Polylactic acid (PLA) can be a good alternative to petroleum-based polymers thanks to its organic origin and its biodegradability. This study introduces some promising routes for enhancing the processability of PLA, which presents several challenges due mainly to the poor shear and elongation properties of this biopolymer. To our knowledge, this is the first paper dedicated to an investigation of foaming and/or blown extrusion of PLA that focuses on structural, rheological and thermomechanical properties. Two main routes were selected: (i) the modification of its structural, rheological and thermomechanical properties and (ii) blending the PLA with another ductile, thermoplastic biopolymer such as poly (butylene adipate-co-terephthalate) (PBAT) or polyamide (PA11). Various formulations of PLA with multifunctionalized epoxy, nucleating agents and plasticizer were prepared and characterized on the basis of their linear viscoelasticity and extensional properties. The balance of chain extension and branching was also investigated using solution viscosimetry, steric exclusion chromatography (SEC) and rheology (shear and elongation rheology). On one hand, a batch foaming process assisted by supercritical CO2 was carried out. The influence of the foaming parameters, the extent of chain modification and the contribution of crystallization to cell morphology were all evaluated. Based on these parameters, structures ranging from micro to macro-cellular-cell were obtained. On the other hand, the stability maps of blown extrusion for neat and modified PLA were established at different die temperatures. We succeeded in greatly enhancing the blown extrusion windows of PLA, achieving high blow-up ratio (BUR) and take-up ratio (TUR) values. We were able to demonstrate that faster kinetics of crystallization can also be reached for chain-extended and branched PLA formulated with adequate amounts of nucleating agents and plasticizers. Through this work, blown films with intriguing thermomechanical and mechanical properties were produced using an optimal formulation for PLA.  Sun, 21 Mar 2021 12:34:49 +0100 https://popups.uliege.be/esaform21/index.php?id=748 https://popups.uliege.be/esaform21/index.php?id=1024 The present work deals with the 3D printing of multimaterials based on PLA/PMMA multilayers directly obtained from pellets. This polymer pair was chosen for their miscibility at the melt state and synergistic properties (i.e., to improve and weather tune the temperature resistance, transparency and thermomechanical properties of their PLA-based materials). Thus, 3D-printed parts with repeating PMMA/PLA/PMMA layers in the Z building direction were successfully prepared in different numbers but maintaining the same composition. The main objective was to better understand the interface/interphase properties developed during this innovative processing. First, further physicochemical and dynamic thermomechanical characterizations were performed. Second, the effects of multi-extrusion 3D printing processing parameters on the thermal stability of PLA, PMMA and their printed specimens were analyzed by GPC. Then, the structuralrheological and mechanical properties of the multilayered systems were investigated in comparison to their equivalent blend. The effects of flow kinematics during extrusion as well as printing chamber temperature (PCT) and infill density (ID) were specifically studied and rationalized. The triggered interfaces were characterized by SEM and subjected to flexural and short-beam three-point bending experiments that proved their dramatic influence on the final mechanical properties. The ultimate aim of this study is to enable successful control of the interfaces/interphases obtained in these 3D-printed PLA/PMMA systems in comparison to other forming processes. Mon, 22 Mar 2021 11:57:27 +0100 https://popups.uliege.be/esaform21/index.php?id=1024 https://popups.uliege.be/esaform21/index.php?id=1589 Food packaging films must be reinvented in order to answer the new demanding ecological requirements. Biobased and/or biodegradable polymers appear as an interesting alternative to reduce petroleum dependence and carbon dioxide emissions. Poly(ethylene furanoate) (PEF) appears today as a new promising biopolymer thanks to its good gas barrier and mechanical properties, despite its high price that could limit its industrial applications. Its combination with other polymers is thus of great interest and for the first time, film coextrusion process is used to create PLA-PEF and PET-PEF multi-micro/nano layered films. A new PEF grade developed by AVA Biochem in the H2020 Mypack program, has been used and firstly analysed in terms of melt processability, mechanical, thermal and gas barrier properties. Our major results confirmed the good gas barrier as well as mechanical properties of amorphous PEF. Post-extrusion PEF bulk thermal crystallization led to very brittle material making gas barrier measurements impossible. Micro/nanolayered PLA-PEF and PET-PEF films with different PEF layer thicknesses have been processed and post-extrusion annealing treatment was carried out. The relationship between crystallinity, mechanical and gas barrier properties will be investigated. Mon, 22 Mar 2021 20:15:25 +0100 https://popups.uliege.be/esaform21/index.php?id=1589 https://popups.uliege.be/esaform21/index.php?id=1985 The effects of PEEK degradation on consolidation of commingled semi-finished products have been investigated. Two commingled semi-finished products provided by two different suppliers have been studied and compared to a powdered fabric based on the same PEEK grade. Both were manufactured from aligned AS4 carbon and PEEK yarns but the first product referred as the NCF1 has a lower commingling level than the second one identified as the NCF2. Contrary to what could be expected, under the same processing conditions, consolidation of the NCF1 and the NCF2 systematically results in a high porosity content, above 10%. Fourier Transform Infrared spectrophotometry (FTIR) in ATR mode and Gel Permeation Chromatography (GPC) have shown small molecular structure modifications of PEEK yarns compared to the raw material, such as a shift of molar mass distributions towards lower molar mass and the appearance of C-H absorption bands attributed to non-aromatic alkanes. These modifications have been attributed to sizing of PEEK filament. Calorimetric (DSC) and rheological analyses have demonstrated that the presence of sizing in the semi-finished products have huge consequences on the degradation kinetics. The crystallization temperature decreases and the viscosity increases significantly. This acceleration of the degradation kinetics is the reason of the poor consolidation behavior during composite manufacturing. The conditions of melt spinning extrusion under which the neat PEEK is transformed into filament are therefore a key factor of PEEK degradation. Tue, 23 Mar 2021 12:20:39 +0100 https://popups.uliege.be/esaform21/index.php?id=1985 https://popups.uliege.be/esaform21/index.php?id=1995 In this paper, an Artificial Neural Network (ANN) is used to predict the stress-strain behavior of PET at conditions relevant to Stretch Blow Moulding i.e. Large equibiaxial deformation at elevated temperature and high strain rate. The input vectors considered are temperature, strain, and strain rate with a corresponding output parameter of stress. In the present work, a feed-forward back backpropagation algorithm was used to train the ANN. The ANN is able to approximate the relationship between stress and strain at various strain rates & temperatures to a high degree of accuracy for all conditions tested. Tue, 23 Mar 2021 12:22:27 +0100 https://popups.uliege.be/esaform21/index.php?id=1995 https://popups.uliege.be/esaform21/index.php?id=2067 Mitigation of cure-induced defects in thermoset composite parts has always been a challenging problem for manufacturers especially when it comes to high dimensional accuracy of components. Thus, it is crucial to understand the evolution of the thermo-chemical properties of these materials during the totality of the curing cycle. In this paper, a new methodology is presented to characterize the process-induced strains throughout the cure. The investigation is based on the development of an existing laboratory bench named as PvT-HADDOC. The tests were performed on an interlayer toughened aerospace carbon/epoxy prepreg. Unidirectional laminate samples (105x105 mm2) of almost 6 mm of thickness were manufactured by hand lay-up then debulked at room temperature under full vacuum. The PvT-HADDOC device allows a manufacturing process following the recommended cure cycle of epoxy composites under 7 bars pressure and a temperature up to 180°C. It enables the measurements of the process-induced strains, simultaneously, along two directions: through-thickness and in-plane. Results show a complex behavior of an assumed unidirectional composite. It exhibits a temperature and time dependent compaction behavior through the thickness only. The measured thermal expansion coefficients are proved to be higher in the thickness direction for the uncured as well as for the cured state of the material. Most of the chemical shrinkage occurs along the thickness direction. This unexpected complexity is mainly attributed to the presence of interleaf layers of resin in the laminate structure. Thus, the investigated M21/IMA material is considered fully orthotropic. Tue, 23 Mar 2021 12:39:08 +0100 https://popups.uliege.be/esaform21/index.php?id=2067 https://popups.uliege.be/esaform21/index.php?id=2788 In this paper, we present an innovative welding process for packaging applications developed by SEALESTER Company. For polymer films, studies have revealed that the welding interface must reach a specific temperature, known as “sealing initiation temperature”, to obtain a sealed joint. In this paper, we will be studying the effect of the process parameters on the evolution of temperature at the welding interface. For this purpose, thermocouples have been placed between the films at different points of the trajectory to measure the temperature evolution. Process parameters and temperature measurements were recorded in each experiment. Results show that the most influential parameters are the temperature and the linear velocity of the tool. Rotational frequency affects the heat distribution on the sealing surface. A minimum pressure must be applied. In conclusion, this new process can produce sealed polymer packages. Future work will consist of studying the quality of obtained seal in addition to optimization and control of the process. Wed, 24 Mar 2021 19:01:59 +0100 https://popups.uliege.be/esaform21/index.php?id=2788 https://popups.uliege.be/esaform21/index.php?id=2816 Infrared welding technology is currently used in the automotive industry to assemble very complex composite shapes made of short glass fiber reinforced polymers. Such applications are targeted more towards short joining times than towards the optimization of adhesive properties. Through this work, the authors joined their efforts on the experimental investigation of driving mechanisms and their optimization, enabling the welding of high-performance materials typically selected for aeronautics applications. The thermal field through the thickness and on the surface was investigated. The best configuration of the LM-PAEK/C laminate presented a single lap shear (SLS) strength of 43.5 MPa with a standard deviation of 0.7 MPa compared to a strength of 24.9 MPa with a standard deviation of 2.3 MPa obtained with the welding configuration without insulation. These results highlight the major effect of a thermal gradient during infrared welding. It is specific to infrared welding to observe that the major resulting defects are located not at the interface area but inside the composite substrate, where voids, generated during the heating step, are unable to be reconsolidated during pressure application. The impact of the decompaction behavior on the thermal gradient was studied through a MATLAB© implemented 1D numerical model, developed internally and called “LysIR”. Wed, 24 Mar 2021 19:05:40 +0100 https://popups.uliege.be/esaform21/index.php?id=2816 https://popups.uliege.be/esaform21/index.php?id=3340 The objective of the present work is to study materials properties and performance of the footwear thread to develop and implement an analytical-numerical model capable of simulating their performance. The numerical results simulation was carried out, analyzing the sliding mechanisms of shoe-floor and evaluating the contact pressure and vertical stress. An experimental procedure, supported by a numerical model, was implemented for computing the evolution of the tangential force over several load increments. Sun, 28 Mar 2021 10:19:19 +0200 https://popups.uliege.be/esaform21/index.php?id=3340 https://popups.uliege.be/esaform21/index.php?id=3814 The main purpose of this study is to better understand the relationship between the microstructure of foamed polymer and mechanical properties. X-Ray tomography was performed on polypropylene foam specimens machined from injected plates. These plates were obtained for different thicknesses and exhibit different microstructure morphologies. The tomography scans were first digitalized and meshed. Then, numerical simulations were performed on representative volume elements (RVEs) to get homogeneous mechanical property of the material using a parallel C++ library Cimlib developed at CEMEF. Numerical methods described in this study focused on immerged or body-fitted strategy (FE context - level set framework - meshing adaptation) for exact and statistical RVEs generation. The numerical results were compared to experimental testing performed under tension and compression at different strain rates using image correlation. Good agreement was observed between simulations performed at the mesoscale and experimental tests carried out at the macroscale for both real and statistical RVEs. This methodology opens a way for the development of digital materials designed for specific mechanical properties. Mon, 29 Mar 2021 14:44:29 +0200 https://popups.uliege.be/esaform21/index.php?id=3814 https://popups.uliege.be/esaform21/index.php?id=4186 Injection molding is a widespread manufacturing technology for mass production of polymeric parts. Conventionally, fused polymers are injected at high pressure in a metallic mold. This tool is typically characterized by high manufacturing costs and times, making the injection molding process not affordable for small batches or prototypal applications. Additive Manufacturing represents a practical solution to cut down tooling costs and times of molds and inserts. In this work, FDM (Fused Deposition Technology) has been considered as candidate technology to produce polymeric inserts for injection molding. Considering the commercially available filaments for FDM, a PEI (Polyetherimide) grade has been selected as tooling material for the injection of a part made of Polypropylene. The PEI grade represents a good compromise between manufacturing costs and thermo-mechanical properties required for the application. The PEI grade has been characterized with DSC (Differential Scanning Calorimetry), DMA (Dynamical Mechanical Analysis) and compression tests. The data gathered were used to set up 2D simplified thermo-mechanical finite element analyses, simulating the response of the PEI inserts subjected to repeated injection molding cycles. The simulations confirmed that the PEI grade is a good candidate tooling material but the progressive tool heating could lead to prolonged cooling time of the Polypropylene part. Finally, some PEI inserts were 3D printed with FDM and tested in a real injection molding machine injecting POM. In total, 20 POM parts have been injected correctly without relevant damaging of the PEI inserts. Thu, 01 Apr 2021 15:01:28 +0200 https://popups.uliege.be/esaform21/index.php?id=4186 https://popups.uliege.be/esaform21/index.php?id=4351 Fiber reinforced thermoplastic composites have shown to be attractive for industry as they can be reused, reshaped, welded and repaired, while keeping mechanical properties on par with thermoset composites. Since thermoplastics usually have high melt viscosities unsuitable for liquid composite molding processes, in-situ synthesis of PA6 from ε-caprolactam is considered. Its reactive mix has low viscosity which allows impregnation. However, the coupled crystallization and polymerization affects the resin viscosity and its flow is altered by the dual-scale permeability of the fiber preform. Thus, to predict the local differences in the thermoplastics properties, a coupled polymerization crystallization model needs to be integrated in the LCM processing simulation at representative scales. This study aims to propose a reliable simulation of the resin flow through a fibrous preform. Hence, viscosity measurements on the reactive mix are achieved using a rheometer with parallel-plate geometry, aiming to associate a viscosity model with the Hillier coupled polymerization-crystallization model previously determined by Vicard. The full chemorheological model will then be integrated into a simulation of LCM process in OpenFOAM®, an open source CFD software in order to follow the extent of the synthesis in the resin flow during the process. As a future work, simulations including microscale tow information extracted from a real textile specimen will permit to investigate the effect of permeability and double scale porosity in fibrous preforms on the final polymerization rate and crystallinity. Thu, 01 Apr 2021 21:46:38 +0200 https://popups.uliege.be/esaform21/index.php?id=4351