Characterization of injection molded polymers – from conventional to wood-based thermoplastics

The success of polymers products is associated with the melt processability, which allows to\ua0create products with complex shapes at a low cost. One of the most widely used processing\ua0techniques utilizing melt processability is injection molding, where a polymer is heated until it\ua0flows into a mold under pressure. Due to varying shear- and cooling rates during processing,\ua0injection molding creates a multilayered structure, consisting of complex hierarchical\ua0morphologies. In addition to process conditions, the structures formed are dependent on the\ua0molecular architecture including chemical environment and branching of the polymer chain.\ua0The resulting morphology defines the mechanical properties of the injection molded parts and\ua0consequently, understanding the correlation between material, processing parameters, and\ua0resulting morphology is an important challenge. Furthermore, to expand the use of injection\ua0molding to renewable cellulosic materials, intrinsic limitation in cellulose that impede melt\ua0processing must be overcome. This can be achieved by chemically modifying the cellulose,\ua0however chemical modifications impact the morphology formed during processing.\ua0This thesis focuses on using advanced scanning small- and wide-angle X-ray scattering as main\ua0characterization techniques, to unfold the nature of the complex semicrystalline structures in\ua0injection molded synthetic and cellulose-based polymers. By varying material parameters,\ua0processing conditions and using complementary techniques, such as computational simulations\ua0and mechanical testing, the underlying factors for formation of hierarchical morphologies is\ua0further studied. This thesis brings us one step closer to understanding and predicting the\ua0polymer microstructures and resulting mechanical properties of injection molded materials

Melt processable cellulose fibres engineered for replacing oil-based thermoplastics

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

Scanning Small-Angle X-ray Scattering of Injection-Molded Polymers: Anisotropic Structure and Mechanical Properties of Low-Density Polyethylene

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

Stem Cell Growth and Migration on Nanofibrous Polymer Scaffolds and Micro-Fluidic Channels on Silicon-Chip

Stem cell growth and migration on nanofibrous scaffolds and micro-fluidic channels on Silicon-Chip were studied by using neural stem cells isolated from adult rats\u27 brain. Electrospinning and lithographic technique were used for developing nanofibrous-polylactic acid (PLA) and polyurethane (PU) based-scaffolds and micro-fluidic channels on Si-Chips respectively. Immunocytochemical and morphological analysis showed better cell-matrix interaction with profound adhesion, proliferation and migration on the developed scaffolds. Cell culture assay with microfluidic channel revealed the ability of developed channel system in guiding neuronal stem cell growth towards specified directions. These studies extend the possibility of using developed nanofibrous scaffolds and micro-fluidic channel system for future electrical signal transmission based on living neural stem cells