| 1. |
- Kroon, Martin, et al.
(författare)
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Anisotropic Elastic-Viscoplastic Properties at Finite Strains of Injection-Moulded Low-Density Polyethylene
- 2018
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Ingår i: Experimental mechanics. - : Springer New York LLC. - 0014-4851 .- 1741-2765. ; 58:1, s. 75-86
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Tidskriftsartikel (refereegranskat)abstract
- Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters. © 2017 The Author(s)
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| 2. |
- Björn, Linnea, 1994, et al.
(författare)
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Process-Induced Structures of Injection-Molded High-Density Polyethylene─Combining X-ray Scattering and Finite Element Modeling
- 2024
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Ingår i: ACS Applied Polymer Materials. - 2637-6105. ; 6:8, s. 4852-4864
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Tidskriftsartikel (refereegranskat)abstract
- The success of plastics heavily relies on fast melt processing methods used for large-scale industrial manufacturing, including injection molding. The hierarchical structure of the solid polymer depends on material selection combined with processing conditions, making mechanical properties of the injection molded part difficult to predict. Here we show how scanning small- and wide-angle X-ray scattering, birefringence microscopy, and polarized light optical microscopy can be combined with injection molding simulations to shed light on the correlation between the polymer morphology of high-density polyethylene and processing conditions. The scattering data revealed that the complex layered structure highly depends on the pressure during the holding phase of injection molding. Furthermore, we identified specific work of flow as a main parameter to capture the changes in morphology induced by varying the process settings. Overall, a good agreement was found between experimental data and the computational simulations, suggesting that computational simulations can be further used to predict the multiphase morphology of injection molded parts.
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| 3. |
- Björn, Linnea, 1994, et al.
(författare)
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Scanning Small-Angle X-ray Scattering of Injection-Molded Polymers: Anisotropic Structure and Mechanical Properties of Low-Density Polyethylene
- 2023
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Ingår i: ACS Applied Polymer Materials. - 2637-6105. ; 5:8, s. 6429-6440
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Tidskriftsartikel (refereegranskat)abstract
- Injection molding is known to create a layered anisotropicmorphologyacross the sample thickness due to varying shear and cooling ratesduring the manufacturing process. In this study, scanning small-angleX-ray scattering was used to visualize and quantify the distributionof hierarchical structures present in injection-molded parts of low-densitypolyethylene (LDPE) with varying viscosities. By combining scatteringdata with results from injection molding simulations and tensile testing,we find that oriented shish-kebab structures, as well as elongatedspherulite structures consisting of semicrystalline ellipsoids, contributeto high ultimate tensile strength along the flow direction. Furthermore,we show that a higher degree of orientation is found close to theinjection gate and in LDPE with higher viscosity, consequently fromelevated shear and cooling rates present during the injection moldingprocess.
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| 4. |
- Ingratta, Mark, et al.
(författare)
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Synthesis, nanostructures and properties of sulfonated poly(phenylene oxide) bearing polyfluorostyrene side chains as proton conducting membranes
- 2011
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:7, s. 2074-2083
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Tidskriftsartikel (refereegranskat)abstract
- Graft copolymers with ionic backbones and hydrophobic fluorinated side chains have been prepared by using lithiated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as a macroinitiator for anionic polymerization of 4-fluorostyrene. After grafting of the poly(4-fluorostyrene) (PFS) side chains, the PPO backbone was selectively sulfonated using trimethylsilylchlorosulfonate under mild and controlled conditions. Microscopy of solvent cast membranes revealed copolymer self-assembly into remarkably regular and well-ordered morphologies which, depending on the molecular structure, included lamellar and cylindrical arrangements of the proton conducting ionic nanophases. Thermal analysis indicated separate glass transitions of the PFS and PPO phases, and high thermal degradation temperatures of the membranes at approximately 220 and 300 °C for the H+ and the Na+ forms, respectively. The proton conductivity of fully hydrated acidic membranes was similar to that of Nafion, reaching above 0.2 S cm−1 at 120 °C. Compared at the same ion exchange capacity, the proton conductivity of the graft copolymer membranes was two times higher than that of a membrane based on an ungrafted sulfonated PPO. The study showed that it is possible to tailor and prepare proton-exchange membranes with well-ordered morphologies and high proton conductivity by employing graft copolymers with a sulfonated backbone bearing hydrophobic side chains.
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| 5. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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Experimental and theoretical study of stress relaxation in high-density polyethylene
- 2024
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Ingår i: Acta Mechanica. - : Springer. - 0001-5970 .- 1619-6937. ; 235:4, s. 2455-2477
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Tidskriftsartikel (refereegranskat)abstract
- Stress relaxation of high-density polyethylene is addressed both experimentally and theoretically. Two types of stress relaxation testing are carried out: uniaxial tensile testing at constant test specimen length and compression testing of a 3D structure producing inhomogeneous deformation fields and relaxation. A constitutive model for isotropic, semi-crystalline polymers is also proposed. The model has the ability to model stress relaxation at different time scales. The developed model was implemented as a user subroutine in Abaqus (UMAT). The implicit integration scheme including an algorithmic tangent modulus is described in detail. The material model is calibrated by use of the uniaxial tensile tests, and the model is then validated by simulating the compression tests of the 3D structure. The model is able to describe the uniaxial tension tests well, and the comparison between the simulations and experimental testing of the 3D structure shows very good agreement. © 2024, The Author(s).
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| 6. |
- Kroon, Martin, Professor, 1974-, et al.
(författare)
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Numerical and experimental analysis of inelastic and rate-dependent buckling of thin injection-moulded high-density polyethylene structure
- 2024
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 290
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Tidskriftsartikel (refereegranskat)abstract
- Semi-crystalline polymers is an important group of materials that is used in a vast array of products. In this study, the rate-dependent properties of high-density polyethylene (HDPE) are investigated, both experimentally and theoretically. Experimental compression testing of a three-dimensional HDPE structure is performed and analysed numerically by use of the finite element method. In addition, an Eulerian constitutive material model for isotropic, semi-crystalline polymers is proposed. The model is able to account for such essential phenomena as strain-rate dependence, work hardening, pressure-dependence of inelastic deformations, and damage. The proposed material model was implemented in Abaqus as a VUMAT, which is an explicit implementation. The material model was calibrated by use of uniaxial tensile tests performed on HDPE dog-bone shaped samples, and the model was further explored by applying the VUMAT implementation to the compression tests of the HDPE structure. The simulation model was able to reproduce the experimental results well, both the uniaxial tests and the compression tests. In particular, the friction present in the compression tests seems to play an important role in determining the buckling mode of the structure.
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| 7. |
- Olsson, Pär A T, 1981-, et al.
(författare)
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Ab initio investigation of monoclinic phase stability and martensitic transformation in crystalline polyethylene
- 2018
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 2:7, s. 7-13
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Tidskriftsartikel (refereegranskat)abstract
- We study the phase stability and martensitic transformation of orthorhombic and monoclimic polyethylene by means of density functional theory using the nonempirical consistent-exchange vdW-DF-cx functional [Phys. Rev. B 89, 035412 (2014)]. The results show that the orthorhombic phase is the most stable of the two. Owing to the occurrence of soft librational phonon modes, the monoclimic phase is predicted not to be stable at zero pressure and temperature, but becomes stable when subjected to compressive transverse deformations that pin the chains and prevent them from wiggling freely. This theoretical characterization, or prediction, is consistent with the fact that the monoclimic phase is only observed experimentally when the material is subjected to mechanical loading. Also, the estimated threshold energy for the combination of lattice deformation associated with the T1 and T2 transformation paths (between the orthorhombic and monoclimic phases) and chain shuffling is found to be sufficiently low for thermally activated back transformations to occur. Thus, our prediction is that the crystalline part can transform back from the monoclimc to the orthorhombic phase upon unloading and/or annealing, which is consistent with experimental observations. Finally, we observe how a combination of such phase transformations can lead to a fold-plane reorientation from {110} to {100} type in a single orthorhombic crystal.
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| 8. |
- Olsson, Pär A T, 1981-, et al.
(författare)
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All-atomic and coarse-grained molecular dynamics investigation of deformation in semi-crystalline lamellar polyethylene
- 2018
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Ingår i: Polymer. - : Elsevier Ltd. - 0032-3861 .- 1873-2291. ; 153, s. 305-316
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we have performed classical molecular dynamics modelling to investigate the effects of different types of force-fields on the stress-strain and yielding behaviours in semi-crystalline lamellar stacked linear polyethylene. To this end, specifically the all-atomic optimized potential for liquid simulations (OPLS-AA) and the coarse-grained united-atom (UA) force-fields are used to simulate the yielding and tensile behaviour for the lamellar separation mode. Despite that the considered samples and their topologies are identical for both approaches, the results show that they predict widely different stress-strain and yielding behaviours. For all UA simulations we obtain oscillating stress-strain curves accompanied by repetitive chain transport to the amorphous region, along with substantial chain slip and crystal reorientation. For the OPLS-AA modelling primarily cavitation formation is observed, with small amounts of chain slip to reorient the crystal such that the chains align in the tensile direction. This force-field dependence is rooted in the lack of explicit H-H and C-H repulsion in the UA approach, which gives rise to underestimated ideal critical resolved shear stress. The computed critical resolved shear stress for the OPLS-AA approach is in good agreement with density functional theory calculations and the yielding mechanisms resemble those of the lamellar separation mode. The disparate energy and shear stress barriers for chain slip of the different models can be interpreted as differently predicted intrinsic activation rates for the mechanism, which ultimately are responsible for the observed diverse responses of the two modelling approaches. © 2018 Elsevier Ltd
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| 9. |
- Persson Jutemar, Elin, et al.
(författare)
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Copoly(arylene ether nitrile) and Copoly(arylene ether sulfone) lonomers with Pendant Sulfobenzoyl Groups for Proton Conducting Fuel Cell Membranes
- 2011
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Ingår i: Journal of Polymer Science. Part A, Polymer Chemistry. - : Wiley. - 0887-624X. ; 49:3, s. 734-745
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Tidskriftsartikel (refereegranskat)abstract
- Three series of fully aromatic ionomers with naphthalene moieties and pendant sulfobenzoyl side chains were prepared via K2CO3 mediated nucleophilic aromatic substitution reactions. The first series consisted of poly(arylene ether)s prepared by polycondensations of 2,6-difluoro-2'-sulfobenzophenone (DFSBP) and 2,6-dihydroxynaphthalene or 2,7-dihydroxynaphthalene (2,7-DHN). In the second series, copoly(arylene ether nitrile)s with different ion-exchange capacities (IECs) were prepared by polycondensations of DFSBP, 2,6-difluorobenzonitrile (DFBN), and 2,7-DHN. In the third series, bis(4-fluorophenyl)sulfone was used instead of DFBN to prepare copoly(arylene ether sulfone)s. Thus, all the ionomers had sulfonic acid units placed in stable positions close to the electron withdrawing ketone link of the side chains. Mechanically strong proton-exchange membranes with IECs between 1.1 and 2.3 meq g(-1) were cast from dimethylsulfoxide solutions. High thermal stability was indicted by high degradation temperatures between 266 and 287 degrees C (1 degrees C min(-1) under air) and high glass transition temperatures between 245 and 306 degrees C, depending on the IEC. The copolymer membranes reached proton conductivities of 0.3 S cm(-1) under fully humidified conditions. At IECs above similar to 1.6 meg g(-1), the copolymer membranes reached higher proton conductivities than Nafion (R) in the range between -20 and 120 degrees C. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 734-745, 2011
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| 10. |
- Persson Jutemar, Elin, et al.
(författare)
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Facile synthesis and polymerization of 2,6-difluoro-2’-sulfobenzophenone for aromatic proton conducting ionomers with pendant sulfobenzoyl groups
- 2010
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Ingår i: Macromolecular Rapid Communications. - : Wiley. - 1022-1336. ; 31:15, s. 1348-1353
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Tidskriftsartikel (refereegranskat)abstract
- The lithium salt of 2,6-difluoro-2′-sulfobenzophenone was conveniently synthesized in one-pot by reacting 2,6-difluorophenyllithium with 2-sulfobenzoic acid cyclic anhydride in THF at −70 °C whereafter the product crystallized out of solution. A poly(arylene ether) and a poly(arylene sulfide) were prepared by polycondensation reactions to demonstrate the reactivity and efficacy of this new monomer to produce sulfonated high-molecular weight aromatic polymers for fuel cell proton-exchange membranes. This work demonstrated that organolithium chemistry may offer versatile and straightforward pathways to new functional monomers with fluorine atoms activated for nucleophilic aromatic substitution reactions.
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