Aim

1. Processing and performance of polymer-clay nanocomposites: implications for processability and performance in medical devices and packagingProf. Eileen Harkin-JonesSchool of Mechanical and Aerospace Engineering

2. Aim • To investigate interactions between process-structure-performance in polymer-clay nanocomposites • To examine the implications for the processing and performance of medical devices and packaging • To highlight areas for future research

3. Polymer nanocomposites Composites in which reinforcing particles have at least one dimension (i.e. length, width, or thickness) on the nanometer scale [1] Surface area: 6 sides of area 5 x 5 = 150 units 125 x (6 sides of area 1 x1 ) = 750 units In going from micro to nano scale the specific surface area increases significantly leading to enhancement of material properties [1] Nanotschnology for engineers-polymer nanocomposites-EPFL-Google

4. Layered silicates or nanoclays The dimensions of a clay platelet are typically 200-1000nm in lateral dimension and 1 nm thick. Can exist in a number of forms TEM of mmt

5. Advantages of polymer-clay nanocomposites strength and stiffness permeation resistance flame retardancy heat deflection temperature because of the large surface area of the nanofiller, only small quantities need be used there should be no need for new processing equipment to mix these fillers into the polymer The composite is recyclable

6. Specific advantages of nanoclays in medical devices and packaging Controlled permeation rates of therapeutic agents in a device Controlled degradation behaviour of devices, packaging [e.g tissue scaffolds, shedding of surface biofilms from tubing] Better high-temperature performance and thus improved performance in sterilisation of packs/devices Extended property range of medical polymers

7. Manufacturing of medical devices and packaging Different processes Catheters – tube extrusion Flexible packaging – blown film extrusion Rigid packaging – thermoforming, stretch blow moulding Biodegradable screws– injection moulding In each case the polymer will experience a particular thermal and deformation history which in turn can be expected to influence structuring and performance

8. Research at QUB Current research at QUB investigating the relationship between processing-structure-performance of polymer nanocomposites Processes of interest include thermoforming and injection stretch blow moulding (ISBM) Focus on PET-clay and PP-clay systems today

9. ISBM & Thermoforming Preform= injection moulded Amorphous PET tube Preform = extruded sheet Essentially biaxial deformation processes

10. Important material parameters for processing Thermoforming Sag resistance of sheet at forming temperature Sheet modulus and yield stress Strain hardening for stability and uniform stretching ISBM Strain hardening behaviour Tcc-Tg temperature processing window

11. Materials & Methods • PET + Somasif synthetic nanoclay - ISBM applications • PP + MMT (Cloisite 15A) + MAH - Thermoforming applications • Materials compounded on twin screw extruder to form pellets • Pellets compression moulded into sheet • Sheet biaxially stretched • Structure characterised using TEM, XRD, DSC, POM • Performance measured using Tensile tests, O2 gas barrier, DMTA

12. Biaxial Stretching ‘preform’ grips top heater temperature sensor Capable of duplicating the deformation behaviour of polymeric materials in ISBM and thermoforming processes.

13. PP-clay

14. Preform: Crystallization behaviour • No change in Xc – shrinkage same • Tc is lower – longer demould times • Longer in melt state – possibly more molecular relaxation but clay is likely to have opposite effect on relaxation

15. Preform: modulus versus temperature • Room temperature modulus is higher for the pp-clay nanocomposite • However, close to forming temperatures the nanocomposite has a lower modulus – likely to cause problems with sheet sagging • Source of reduction – early melting of smaller spherulites in pp-clay sheet

16. Preform: Deformation behaviour No difference in strain hardening behaviour

17. Preform: Temperature sensitivity • At 145 C the yield stress for the pp-clay is 25% greater than the unfilled pp- will require greater forming forces at this temperature • At 150 C no obvious difference in yield behaviour

18. Effect of stretching on structure SR=1.0 SR=1.5 SR=2.0 SR=3.0 SR=2.5 SR=3.5 Stretching helps delaminate clay stacks and causes orientation of platelets

19. Platelet thickness distribution

20. Orientation distribution SR=1.0 SR=2.0 SR=1.5 SR=2.5 SR=3.5 SR=3.0

21. Exfoliation number - N The exfoliation number (N) is defined as the percentage of the total clay interfacial area that is exposed to the polymer matrix. It is a dimensionless quantity, which ranges from 0 to 100, with 0 indicating no exfoliation and 100 indicating complete exfoliation.

22. Exfoliation number Large increase between SR=3 and SR=3.5

23. Mechanical & barrier properties of stretched sheet • Increase in exfoliation as SR increases • Main improvement is in barrier and yield strength • Improvement in yield may be connected to crystallite size modification

24. High temperature performance Cross-over=70 0C Cross-over=100 0C As N increases the reduction in nanocomposite modulus due to early crystallite melting is compensated for by the greater contribution of the clay. Cross over temperature Increases.

25. PET-Clay

26. Preform : Crystallization behaviour • Tcc-Tg = temperature processing window. • Slight reduction with incorporation of clay (2 ⁰C)

27. Preform : modulus versus temperature • Addition of clay enhances high temperature modulus • Less likely to have problems with sag (extrusion blow moulding) • Unlike behaviour of PP-clay system

28. Preform : deformation behaviourEqui-biaxial stretching, strain rate 8/s, T = 100 °C Note: SR=Nominal +1 • Clay inclusion leads to large increase in strain hardening even at 1wt% • At 5wt% and nominal strain =1.8 would need 90% more work energy to deform the PET-clay material

29. Effect of stretching on structure Unstretched SR=3.0 Stretching Tactoid folding and bending

30. Effect of stretching on tactoid thickness Stretching conditions – stretch ratio 3; strain rate 8/s; temp. 100 deg C) • Stretching causes increase in the concentration of tactoids having thickness 1-2 nm . • Tactoids having 5-10 and 10-15 nm thickness are higher for the unstretched sheet.

31. Orientation distribution SR=2 SR=1.0 SR=2.5 SR=3.0

32. Mechanical & barrier properties of stretched sheet • Even in the unstretched state and at low exfoliation level the clay has a significant effect on modulus and barrier enhancement. This may be due to the high aspect ratio of this clay N [particle length 1200nm compared with 200nm for Cloisite 15A]. • Increasing the SR increases the particle alignment which contributes further to modulus enhancement

33. Mechanical & barrier properties of stretched sheet • At SR=3 strain induced crystallinity and molecular orientation increase the modulus of the matrix and the contribution of the clay is less important. • O2 barrier enhancement better than pp-clay system in unstretched state – probably due to higher aspect ratio. • At SR=3 strain induced crystallinity and molecular orientation increase the barrier of the matrix and the contribution of the clay is less important

34. High temperature performance Equi-biaxial stretching, strain rate 8/s, T = 100 °C • Significant enhancement in storage modulus at high temperatures

35. Implications for processing and performance of medical devices and packaging

36. Processing Be aware that addition of clay may alter temperature processing windows and forming forces required Sag resistance of preforms can be improved or reduced depending on the base polymer and the influence of clay on crystallite perfection

37. Processing Should achieve more uniform wall thickness in PET-clay products due to increased strain hardening Pre-orientation of clay in a preform will further significantly increase forming forces required for deformation in that direction make preforms with as little orientation as possible (difficult in injection moulded preforms, ok for sheet)

38. Processing For the materials studied in QUB to date (PP, PET, HDPE) the incorporation of clay does not alter the crystallinity levels so shrinkage should not be different for the clay filled systems. Demould times may be longer as Tc tends to be reduced [may be different for other materials]

39. Performance It is possible to attain good levels of O2 barrier enhancement with low addition levels of clay in PP and PET Modulus enhancement is much better (at both room and higher temperatures) in the PET system at the same SR – possibly due to the larger aspect ratio of clay used in PET since exfoliation levels are actually higher in PP Varying stretch ratio provides a means to control exfoliation levels and hence performance e.g drug release rates could be controlled.

40. Performance Clay: aspect ratio, degree of alignment, potential for bending and twisting Changes in crystallite size and size distribution due to presence of clay Changes in % Xc due to nucleating effect of clay Increased capacity for molecular entanglement due to presence of nanoscale particles – more ‘crosslink’ points Strength of interaction between clay and polymer Matrix modulus relative to clay modulus – greater effect in a softer matrix Degradation of matrix Possible sources of property change

41. Performance In the composites made to date we are still not close to full exfoliation. - will incorporate more extensional flow in the actual compounding stages to try and improve this. - will also look at higher SRs to determine if exfoliation continues to increase

42. Potential future work Incorporation of conductive particles – use of different stretching regimes to impart tailored anisotropic electrical properties Determine influence of structuring on release of therapeutic agents Determine effects of sterilising environments on performance of polymer-clay devices/packaging Incorporate clay into polymers with Tg close to 37 C and examine switching capacity

43. Acknowledgements Academic Staff • Prof. C. Armstrong • Prof. P. Hornsby • Dr M. McAfee • Dr T. McNally • Dr P.Martin • Dr G.Menary Research Fellows • Dr J. Hill • Dr R.Rajeev • Dr S. Xie • Dr Richard O’Shaughnessey PhD students • R.Abu-Zurak • Y.Shen • K.Soon