| 1. |
- Björn, Linnea, 1994
(author)
-
Characterization of injection molded polymers – from conventional to wood-based thermoplastics
- 2022
-
Licentiate thesis (other academic/artistic)abstract
- The success of polymers products is associated with the melt processability, which allows to create products with complex shapes at a low cost. One of the most widely used processing techniques utilizing melt processability is injection molding, where a polymer is heated until it flows into a mold under pressure. Due to varying shear- and cooling rates during processing, injection molding creates a multilayered structure, consisting of complex hierarchical morphologies. In addition to process conditions, the structures formed are dependent on the molecular architecture including chemical environment and branching of the polymer chain. The resulting morphology defines the mechanical properties of the injection molded parts and consequently, understanding the correlation between material, processing parameters, and resulting morphology is an important challenge. Furthermore, to expand the use of injection molding to renewable cellulosic materials, intrinsic limitation in cellulose that impede melt processing must be overcome. This can be achieved by chemically modifying the cellulose, however chemical modifications impact the morphology formed during processing. This thesis focuses on using advanced scanning small- and wide-angle X-ray scattering as main characterization techniques, to unfold the nature of the complex semicrystalline structures in injection molded synthetic and cellulose-based polymers. By varying material parameters, processing conditions and using complementary techniques, such as computational simulations and mechanical testing, the underlying factors for formation of hierarchical morphologies is further studied. This thesis brings us one step closer to understanding and predicting the polymer microstructures and resulting mechanical properties of injection molded materials.
|
|
| 2. |
- Björn, Linnea, 1994, et al.
(author)
-
Process-Induced Structures of Injection-Molded High-Density Polyethylene─Combining X-ray Scattering and Finite Element Modeling
- 2024
-
In: ACS Applied Polymer Materials. - 2637-6105. ; 6:8, s. 4852-4864
-
Journal article (peer-reviewed)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.
|
|
| 3. |
- Björn, Linnea, 1994, et al.
(author)
-
Scanning Small-Angle X-ray Scattering of Injection-Molded Polymers: Anisotropic Structure and Mechanical Properties of Low-Density Polyethylene
- 2023
-
In: ACS Applied Polymer Materials. - 2637-6105. ; 5:8, s. 6429-6440
-
Journal article (peer-reviewed)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.
|
|
| 4. |
- Lo Re, Giada, 1971, et al.
(author)
-
Melt processable cellulose fibres engineered for replacing oil-based thermoplastics
- 2023
-
In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 458
-
Journal article (peer-reviewed)abstract
- If cellulosic materials are to replace materials derived from non-renewable resources, it is necessary to overcome intrinsic limitations such as fragility, permeability to gases, susceptibility to water vapour and poor three-dimensional shaping. Novel properties or the enhancement of existing properties are required to expand the applications of cellulosic materials and will create new market opportunities. Here we have overcome the well-known restrictions that impede melt-processing of high cellulose content composites. Cellulose fibres, partially derivatised to dialcohol cellulose, have been used to manufacture three-dimensional high-density materials by conventional melt processing techniques, with or without the addition of a thermoplastic polymer. This work demonstrates the use of melt processable chemically modified cellulose fibres in the preparation of a new generation of highly sustainable materials with tuneable properties that can be tailored for specific applications requiring complex three-dimensional parts.
|
|
| 5. |
- Soliman, Ahmed Elmahdy, 1994, et al.
(author)
-
Ischemic preconditioning affects phosphosites and accentuates myocardial stunning while reducing infarction size in rats.
- 2024
-
In: Frontiers in cardiovascular medicine. - 2297-055X. ; 11
-
Journal article (peer-reviewed)abstract
- Ischemic preconditioning (IPC), i.e., brief periods of ischemia, protect the heart from subsequent prolonged ischemic injury, and reduces infarction size. Myocardial stunning refers to transient loss of contractility in the heart after myocardial ischemia that recovers without permanent damage. The relationship between IPC and myocardial stunning remains incompletely understood. This study aimed primarily to examine the effects of IPC on the relationship between ischemia duration, stunning, and infarct size in an ischemia-reperfusion injury model. Secondarily, this study aimed to examine to which extent the phosphoproteomic changes induced by IPC relate to myocardial contractile function.Rats were subjected to different durations of left anterior descending artery (LAD) occlusion, with or without preceding IPC. Echocardiograms were acquired to assess cardiac contraction in the affected myocardial segment. Infarction size was evaluated using triphenyl tetrazolium chloride staining. Phosphoproteomic analysis was performed in heart tissue from preconditioned and non-preconditioned animals. In contrast to rats without IPC, reversible akinesia was observed in a majority of the rats that were subjected to IPC and subsequently exposed to ischemia of 13.5 or 15min of ischemia. Phosphoproteomic analysis revealed significant differential regulation of 786 phosphopeptides between IPC and non-IPC groups, with significant associations with the sarcomere, Z-disc, and actin binding.IPC induces changes in phosphosites of proteins involved in myocardial contraction; and both accentuates post-ischemic myocardial stunning and reduces infarct size.
|
|
