Evaluating shape memory behavior of polymer under deep-drawing conditions

Thermoplastic polyurethanes (TPU) are a popular family of shape memory polymers (SMP) due to their excellent abrasion & weather resistant, and mechanical strength. However, conventional processing operations or their combination with other polymers by adhesion or blending can affect their unique shape memory behavior. Currently, there are no effective methods to study and quantify the shape memory behavior of SMP based polymer laminates as they would respond to deep drawing operations. In this paper, a new method was introduced to effectively quantify the recovery behavior of TPU based polymer laminates undergoing simultaneous stretching and bending operations at different processing temperatures. The results presented show the value of developing a shape recovery characterization method that resembles the stresses of thermoforming to properly assess formability of shape memory polymers used in laminate constructions.     

BIAXIAL DEFORMATION BEHAVIOR OF PET DEPENDENT ON TEMPERATURE AND STRAIN RATE

Due to its material properties, PET is a very interesting and challenging material for thermoforming applications. During the thermoforming process it may be subjected to high deformations at elevated temperatures. Plug assisted deformation of PET was executed with a servo-hydraulic testing machine utilizing a special clamping device. The effect of strain induced crystallization for bi-axial deformation was investigated at different temperatures and strain rates. The influence on morphology and crystallization was investigated by x-ray diffraction and scattering as well as DSC measurements. The process of crystallization was investigated for different processing parameters. Although still transparent, the stretched PET has changed to a semi-crystalline material with distinct WAXD patterns known from uni-axial deformation.     

Industrially produced PET nanocomposites with enhaced properties for food packaging applications

Gas permeation of polymers is one of the important factors to be considered in the selection of materials for many packaging applications, such as modified atmosphere packaging (MAP) for foods. Poly (ethylene therephthalate) (PET) is known to exhibit very low gas permeation compared with most polymers such as polystyrene, polyethylene and polypropylene. However, MAP applications require better barrier performance than that of PET. In the present work PET trays reinforced with organically modified sepiolite, fibrillar nanoclay, have been produced at industrial processes. Permeability to water vapour, oxygen and carbon dioxide has been studied in PET nanocomposites as well as their microstructure through transmission electron and scanning electronic microscopy (TEM and SEM), and their mechanical properties. Results show a better performance in barrier properties as well as an increase in tensile strength, and impact resistance when the sepiolite content is lower than 2.5%.     

Long chain branching on linear polypropylene by solid state reactions

A method was developed for the long chain branching (LCB) of isotactic polypropylene (iPP) via modification in the solid state. PP long chains have been linked as branches to the original linear iPP chains using solid state reactions in the presence of a free radical initiator and a multifunctional monomer (co-agent). The modified samples of branched iPP were characterised by gel permeation chromatography (GPC) and rheological measurements. Several methods were applied in order to estimate indirectly the extent of branching. A ranking was made of the co-agents according to their ability in inducing LCB as opposed to cross-linking and degradation of iPP. The furfuryl sulphide (FS) showed the highest efficiency for the branching reaction, while the divinylbenzene (DVB) is not suitable for branching.