Additive Manufacturing of Polyolefins.

Polyolefins are semi-crystalline thermoplastic polymers known for their good mechanical properties, low production cost, and chemical resistance. They are amongst the most commonly used plastics, and many polyolefin grades are regarded as engineering polymers. The two main additive manufacturing techniques that can be used to fabricate 3D-printed parts are fused filament fabrication and selective laser sintering.

Melting Kinetics of Nascent Poly(tetrafluoroethylene) Powder.

The melting behavior of nascent poly(tetrafluoroethylene) (PTFE) was investigated by way of differential scanning calorimetry (DSC). It is well known that the melting temperature of nascent PTFE is about 344 ∘ C, but reduces to 327 ∘ C for once molten material. In this study, the melting temperature of nascent PTFE crystals was found to strongly depend on heating rate, decreasing considerably for slow heating rates.

Three-dimensional printing of hierarchical liquid-crystal-polymer structures.

Fibre-reinforced polymer structures are often used when stiff lightweight materials are required, such as in aircraft, vehicles and biomedical implants. Despite their very high stiffness and strength, such lightweight materials require energy- and labour-intensive fabrication processes, exhibit typically brittle fracture and are difficult to shape and recycle. This is in stark contrast to lightweight biological materials such as bone, silk and wood, which form by directed self-assembly into complex, hierarchically structured shapes with outstanding mechanical properties, and are circularly integrated into the environment.

Characterization and modelling of Langmuir interfaces with finite elasticity.

Interfaces differ from bulk materials in many ways, one particular aspect is that they are compressible. Changing the area per molecule or per particle changes the thermodynamic state variables such as surface pressure. Yet, when compressing to high surface pressures, dense packing of the interfacial species induces phase transitions, with highly structured phases, which can display elastic or strongly viscoelastic behaviour.

From drop-shape analysis to stress-fitting elastometry.

Drop-shape analysis using pendant or sessile drops is a well-established experimental technique for measuring the interfacial or surface tension, and changes thereof. The method relies on deforming a drop by either gravity or buoyancy and fitting the Young-Laplace equation to the drop shape. Alternatively one can prescribe the shape and measure the pressure inside the drop or bubble using pressure tensiometry.

Modeling energy storage and structural evolution during finite viscoplastic deformation of glassy polymers.

The enthalpic response of amorphous polymers depends strongly on their thermal and deformation history. Annealing just below the glass transition temperature (T_{g}) causes a large endothermic overshoot of the isobaric heat capacity at T_{g} as measured by differential scanning calorimetry, while plastic deformation (cold work) can erase this overshoot and create an exothermic undershoot. This indicates that a strong coupling exists between the polymer structure, thermal response, and mechanical deformation.

Small hook thread (Quill) and soft felt internal splint to increase the primary repair strength of lacerated rabbit Achilles tendons: biomechanical analysis and considerations for hand surgery.

Background: For the prevention of re-rupture during early healing phase, the primary repair strength of repaired lacerated tendons in hand surgery should be maximal and the reconstructed diameter minimal. Two new repair methods (small hook thread and internal splint) were assessed for strength and reconstructed diameter characteristics.

Methods: Achilles tendons of 43 female New Zealand White rabbits were sectioned 2 cm above the calcaneus.

The effect of size and density on the mean retention time of particles in the reticulorumen of cattle ( Bos primigenius f. taurus), muskoxen ( Ovibos moschatus) and moose ( Alces alces).

Particle passage from the reticulorumen (RR) depends on particle density and size. Forage particle density and size are related and change over time in the RR. Particle density mainly influences sorting in the reticulum, whereas particle size influences particle retention in the fibre mat of stratified rumen contents ('filter-bed' effect).