Flexible PCL tube scaffolds by winding of micro-extruded filaments

An important requirement for tissue engineering scaffolds is matching of the functional me-chanical properties to their natural tissue counterpart. Specifically for arteries this comprises the elastic re-sponse of the vessel wall to blood pressure. Human aorta has a low elastic modulus when compared to some FDA-approved synthetic polymer materials frequently used in tissue engineering. The current research en-deavours to expand the existing production technology of 3D plotting to winding of micro-extruded filaments in order to obtain flexible polymer tubes with continuous fibre. Tube scaffolds are manufactured by conven-tional 3D plotting and by winding. Their structure and quasi-static mechanical properties are evaluated and compared to human aorta. Winded tubes are found to be far more suitable for application as a blood vessel scaffold than their 3D plotted counterparts

Micro-extrusion of thermoplastics for 3D plotting of scaffolds for tissue engineering

This doctoral research has focused on the feasibility of manufacturing adequate scaffolds for cardiovascular tissue engineering through the technique of 3D plotting micro-extruded filaments of biodegradable thermoplastics. Two aspects were addressed, the foremost of which encompasses the production and evaluation of poly-ε-caprolactone (PCL) scaffolds for the replacement of arteries and heart valve cusps. Scaffolds with different geometries were created and their relevant mechanical properties were compared to those of the equivalent natural tissue. To improve their cell-interactive properties, a method was developed for coating the PCL parts with collagen. In a second aspect, the expansion of this production technique to the micro-extrusion for 3D plotting of thermally sensitive polymers like poly-(lactic acid) (PLA) was considered. A finite element model of the conventional dispense head for thermoplastics revealed that its thermoregulation was unsuitable for the processing of PLA-based polymers, which were found to degrade significantly during their residence time inside the dispense head. Hence, a new dispense head named COMET (COntinuous Modular Extrusion of Thermoplastics) was developed to reduce thermal loading of the polymer during processing. COMET was found to be a functional device with a much improved thermoregulation, which will allow for the reliable extrusion of thermally sensitive polymers

The Effect of Injection Moulding Temperature on PET Particles/Fibrils in Blends and MFCs

The microfibrillar composites of polypropylene (PP)/poly(ethylene terephthalate) (PET) have been prepared by twin-screw extrusion, followed by cold drawing. The employed stretch ratio was 4. Further processing was done by injection moulding at three different processing temperatures (210ºC, 230ºC, 280ºC) on PP/PET blends with wt% 70/30 Samples were subjected to extensive characterization in each step of MFC preparing. Fourier Transform Infrared (FTIR) spectroscopy was employed to determine the nature of the interaction between the polymers in the composites.. Thermogravimetric Analysis (TGA) were used to investigate degradation of polymers. The crystallization, melting behaviour and the crystallization morphology were investigated by Dynamic Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). Influence of processing temperature on morphology was investigated by using Scanning Electron Microscopy (SEM). The observations from the fracture surfaces were discussed and compared with the mechanical properties, and the results have shown a significant influence of the injection moulding temperature on the morphology development and mechanical properties

Influence of processing parameters and composition on the effective compatibilization of polypropylene–poly(ethylene terephthalate) blends

The effects of the addition of different functionalized compatibilizers on toughness, morphology and rheological properties of a polypropylene (PP) - poly(ethylene terephthalate) (PET) (85-15 wt%) blend were studied. The three compatibilizers compared were: (Styrene Ethylene Butylene Styrene)- grafted(glycidyl methacrylate); (Styrene Ethylene Butylene Styrene) - grafted - (maleic anhydryde); (polyolefin) - grafted - (glycidyl methacrylate), abbreviated to: SEBS-g-GMA, SEBS-g-MA and POE-g-GMA respectively. The effective grafting content was the same for all three compatibilizers. Before the comparison of the different compatibilizers was done, first the effects of three different processing temperatures and three different compatibilizer contents were investigated, based on the addition of SEBS-g-GMA. The compatibilization effect was significantly improved with an increase in processing temperature from 250 to 300 degrees C. The toughness was increased with almost a factor two and a decrease in the average domain size of the dispersed phase was observed. An increase in compatibilizer content from 0.25 to 2.5 wt% resulted in a finer dispersity as well as in a steep increase in toughness, which was noted to approach the brittle-to-ductile transition. The comparison of the three compatibilizers was subsequently done at the most promising processing temperature and content: 300 degrees C and 2.5 wt%. The results showed that the addition of SEBS-g-MA and POE-g-GMA had a less significant positive effect on the compatibilization compared to SEBS-g-GMA. The difference is attributed to a higher reactivity for GMA compared to MA and a higher possibility for migration towards the PP-PET interface for the SEBS chain compared to the POE chain

The influence of draw ratio on morphology and thermal properties of MFCs based on PP and PET

The main goal of this study is to investigate the influence of draw ratio on morphology and properties in microfibrillar composites (MFCs). In situ MFCs based on polypropylene (PP) and poly(ethylene terephthalate) (PET) have been prepared at the weight ratio of 80/20 by twin-screw extrusion, followed by cold drawing and injection moulding. In order to study the differences in MFCs caused by draw ratio, the samples were prepared at different ratios and subjected to extensive characterization in each step of the MFC preparation process. The morphology of MFC and influence of draw ratio were investigated by using Scanning Electron Microscopy (SEM). The thermal decomposition of the polymers in MFCs was studied by Thermogravimetric Analysis (TGA), the melting and crystallization behaviour by Dynamic Scanning Calo-rimetry (DSC)

The effect of the compatibilizer SEBS-g-GMA on the blend PP-PET: virgin and recycled materials

Abstract. In the carpet industry poly(ethylene terephthalate) (PET) and poly(propylene) (PP) are often used together within a single product. Mechanical recycling of these carpets results in a blend of PET and PP, which are immiscible. To enhance impact strength of this waste stream, the compatibilizer SEBS-g-GMA was used. More specific the transferability of earlier results with the compatibilizer, obtained on virgin PET-PP blends with amorphous PET (PETg), was assessed. Firstly, from these blends to blends with semi-crystalline PET (PETe) and secondly, from virgin to recycled materials. Two blends of virgin material were made containing 80 wt% PP and 20 wt% PETg or PETe. The effect of adding 2,5 wt% SEBS-g-GMA was assessed. Subsequently, post-industrial PP (r-PP) and post-consumer PETe (r-PETe) were blended and mechanical properties were measured for blends with and without compatibilizer. An increase in impact strength for the two virgin compatibilized blends (PP:PETg:SEBS-g-GMA and PP:PETe:SEBS-g-GMA) was expected and confirmed. A reduced effect of the compatibilizer on impact strength was observed for the recycled blends, due to the possible presence of contaminants. It was concluded that the results from virgin PETg-PP were directly transferable to virgin PETe-PP, but not entirely to recycled materials