Supervisor: Dr. Marion McAfee
Funding body: Institute of Technology, Sligo Presidents Bursary Award
The scope of this project is to investigate the processing of biodegradable polymers and develop models which can indicate changes in key end product material properties – which are currently assessed offline – in real time using available system data. The creation of models to predict these properties inferred from processing data which is available on extrusion based production lines would prove a significant advancement in the development of biodegradable polymer products.
The industry faces a number of issues regarding the processing of these polymers and their Quality Assurance once processed. Identification and control of suitable processing conditions is extremely challenging usually relying on trial and error and this leads to material and machine specific solutions to processing problems that occur for manufacturers. A change of the batch of material although of the same classification may require a new period of trial and error to find suitable production settings for the -“new”- batch of material. Quality assessment requires off-line testing in laboratory environments which result in high scrap rates, long lead times and lengthy and expensive process development. Typical scrap rates are in the region of 25-30% for medical grade bioresorbable polymers which bear a large expense.
The material under investigation in this study is PLA (Polylactide), this is a biodegradable polymer made from renewable resources such as corn starch. PLA is used for a variety of applications including medical devices, food packaging and waste disposal packaging. The grades of PLA used for each of these applications are varied and it is an aim that the work that is carried out here will contribute to the improved process control and process optimisation regardless of the material grade and final application. Much of the development work will be done using a packaging grade of PLA as this is a much more cost effective way of developing the models. This PhD study supports the wider FP7 ‘Bio-PolyTec’ project. Data which will be gathered within ‘Bio-PolyTec’ by our project partners in Tampere University of Technology (TUT) Finland from processing of medical grade PLA will contribute to the aims of this PhD project. It is a goal of this study that it is not restricted to the extrusion equipment that it is carried out on; that the methods created can be applied to other extruders. It is an aim that with further research that any methodology used to create and validate tools for prediction of key material properties on line during processing can be further extended to other biodegradable polymers.
Additives are used to enhance final properties of the processed polymers as they can improve certain characteristics of the end material including mechanical properties, and degradation rate as well as improving biocompatibility or having a therapeutic function in the case of medical implants. They can also reduce the cost of the product as less of the polymer resin is required. After careful consideration of the literature on the topic it was decided to use calcium carbonate (CaCO3) as filler for these trials as it has potential to be used with all grades of PLA for medical or packaging applications. Fillers improve mechanical properties by increasing the Young’s modulus, % elongation at break of the composites and impact strength. These properties provide a more robust end product for its application. Additives are advantageous when used in temporary medical devices, for example the release of calcium from orthopaedic implants such as fixation screws promotes healing.