Introduction
Each year hospitals in the Netherlands generate approximately 1.3 million kilogram of waste from the polypropylene (PP) wrapping paper (WP) used to wrap surgical instruments. The objective of this thesis is to acquire high quality PP, for the use of injection moulding, from blue wrapping paper waste as well as analysing and proposing solutions for optimizing the current melting process.
Method
In the first part of this thesis the WP was melted at different temperatures into bars, granulated and mixed with virgin PP. Dog bones were injection moulded to analyse the influence of the initial melting temperature, mixing ratio with virgin, pollution (sticker and tape) and ten washing cycles of disinfection at the sterilization department.
The reduction of the cycle time by means of pressure was analysed on a conceptual level. The separation of the pollution from the WP during the melting cycle with filtration was tested with three different filter designs. Finally, partitioning of the end product with a tray divider was tested.
Results
The results on the initial melting temperature show marginal differences in material properties. In general the reprocessed material behaves in a more brittle manner, with the ultimate tensile strength, Young's modulus and Shore D hardness increasing and the strain at break decreasing with amount of WP recyclate used compared to virgin material. Pollution seemed to decrease the strain at even further while also decreasing the ultimate tensile strength. The results for the washing and disinfection showed minimal material changes.
The results on the tested filtration prototypes showed that filtration can be used to separate pollution during the melting cycle. Furthermore, IR temperature measurements and flow measurements, with clean and polluted WP waste, show the importance of heat flow characteristics for an efficient filter design. The combination of a filter with proper heat flow characteristics and a conceptual pressure system showed a weight reduction of 40%. The tray divider partitioned the end product, making the end product directly implementable in a granulator.
Discussion
The changes in material properties when using 50% virgin material and 50% recyclate (50%R) indicated minimal changes when compared with 100% virgin. Moreover, this does not imply a lesser product, rather a different product. Different applications require different material properties, as such the mixing ratio can be adapted according to the applications needs.
When designing a full-scale filter it is recommended to use spikes to keep the bulk of the pollution from reaching the permeable surface of the filter. The use of a coating on a filter could reduce the time needed to clean the filter.
Conclusion
This thesis project showed that it possible to make high-quality products with the granulate obtained from blue wrapping paper waste. Also, adding; a pressure system, a filtration system and a tray divider can reduce the process time for obtaining 99% pure granulate from WP waste.