Greening Plastics: Modifying plastics with functional additives based on condensed tannin esters

1. Greening Plastics: Modifying plastics with functional additives based on condensed tannin esters Warren Grigsby Jamie Bridson, Cole Lomas Carmen Schrade and Jaime-Anne Elliot warren.grigsby@scionresearch.com

2. Overview • Highlights of a greater study evaluating tannin esters in plastics • Introduction • Tannins & plastic additives • Tannin esters in plastics • Filler v compatible, active ingredient • Providing functional equivalence • Specific performance

3. Introduction: Condensed Tannins • Nature provides a range of condensed tannins • Leaf, fruit, stem and bark • Provide a protection role for plant/tree • Secondary metabolites • Polyphenolic structure • Extractable n Procyanidin: flavonoid base structure

4. Tannins: Providing Function • Blueberries, bark, wine,… • antioxidant, protein inhibition, UV absorption • Neutriceuticals, food, industrial • oxidative stress-cognitive function • protein inhibition • antimicrobial • tanning leather

5. Plastic Additives: Adding Performance • Additives provide functionality and longevity • colour, flame retardant, plasticizers • Longevity • antioxidants and UV stabilisers • not so well known • synthetic, petrochemical • BHT, hindered amines • Why not bio?

6. Tannins: Synthetics & Plastics • Tannin usually a crosslinked molecule in adhesives • Phenol formaldehyde, Bakelite chemistry • PLA plastic modified with tannins • reinforcement, melt-spun filaments • Electrospinning protein nanofibres • tannin → functionality 10mm 10mm Grigsby, Kadla, Macromolecular Materials and Engineering, 299(3) 2013 368–378. Dallmeyer, Grigsby, Kadla, J Wood Chem Tech 33(3) (2013) 197-207.

7. Aims & Goals • Can functionality a tree uses be applied to plastics? Hypothesis • Tannin efficacy in bark can be applied to protect plastics from oxidative aging and UV-induced degradation • Evaluate tannins as bio-sourced plastic additives

8. Tannins & Chemical Modification • Tannins: water soluble extracts → inherently hydrophilic • Modify → change miscibility/compatibility with plastics Tannin + Alkyl Anhydride Tannin Esters C2–C6 chain length Mixed Esters R1,2 = Ac, Pr, Bu, Hex… Vary: Degree of substitution (DS) Antioxidant Capacity Macromolecular properties UV absorption Grigsby, et al. Polymers, 2013, 5(2), 344-360

9. Tannins & Chemical Modification Change melt behaviour • Tannins: water soluble extracts → inherently hydrophilic • Modify → change miscibility/compatibility with plastics Tannin + Alkyl Anhydride Vary UV absorption Tannin Esters C2–C6 chain length Mixed Esters Vary: Degree of substitution (DS) Antioxidant Capacity Macromolecular properties UV absorption

10. Plastic Processing & Evaluation • Tannin esters compounded in plastics 0-10% w/w Master Batch Tannin Ester (10%) compounded with plastic PP, PBS PLA, PHA, PHB Injection Moulded ASTM Test specimens Flexural & Tensile bars Extrusion MB blended with plastic 0%, 0.5%, 1%, 3%, & 5%, 10% Fluorescence & light microscopy Thermal Analysis DSC, TGA, DMTA Mechanical Testing Flex & Tensile Accelerated Aging Thermally UV & weathering

11. Plastic Additive or Filler? • Longer ester chains show progressive solubility and diminished particle domains within PLA • TanAc (C2) retained as distinct domains → poor miscibility or phase separation • TanHex (C6) → fully dispersed within the plastic TanAc TanPr TanBu TanHex (image 500 x 500 m) Confocal microscopy: PLA containing 5% tannin esters using tannin inherent autofluorescence Grigsby, et al. Polymers, 2013, 5(2), 344-360

12. Plastic Additive or Filler? • Tannin esters contribute up to 15% decreased PLA stiffness • ester chain length & greater content decrease MOE • native tannin stiffens PLA → acts as a filler TanAcC2 Ester Native Tannin Short Chain C3-C4 Esters LongerChain C6 Esters

13. Plastic Polymer Properties • Crystallization decreased • melt temp. unchanged • 10% C6 esters lower PLA Tg • reduced effect • lower ester quantity • shorter chain length DMTA DSC Crystallisation Tg Melt • At typical additive content minimal impact on polymer properties

14. Thermal & Oxidative Stability TGA • Reprocessed PP (up to 10x)→ reduced thermal stability • 10% TanHex → increase thermal stability  potential to lower plastic oxidative degradation on processing Increased thermal stability • Tannin esters promote plastic thermal stability • Oxidation induction time (OIT) • TanHex in PP → increased OIT, TanHexAc→ not  residual antioxidant capacity important Grigsby, et al., Macromolecular Materials and Engineering, 299 (10) (2014)1251–1258.

15. Plastic Accelerated Aging • Tannin esters provide UV stability on aging polypropylene • biopolyesters challenged by aging Native Tannin LongerChain C6 Ester Mixed C2-C6 Esters Mechanical properties before/after UV and condensation exposure cycling

16. Accelerated Aging • Bionolle (PBS) samples increase in stiffness • tannin hexanoate ester → excellent flexural strength retention • similar results on thermal aging Native Tannin Mixed C2-C6 Esters LongerChain C6 Ester • Functional equivalency comparable to commercial UV stabilisers Grigsby et al, J. Appl. Polym. Sci., 132(11) (2014) 41626

17. Colour Stability and UV inhibition • Accelerated Aging → plastic colour tended to surface bleach • seen as undesirable, but gauge for tannin efficacy • Measure efficacy Intensity across the surface Visible bleaching White Intensity 0.24 mm • Tannin sacrificial  bleach depth → extent of UV inhibition • PBS: TanHex0.25 mm v. TanAc 0.47 mm • consistent with tannin dispersion by microscopy Grigsby et al, J. Appl. Polym. Sci., 132(11) (2014) 41626

18. Take home information • Tannin esters can be functional additives in biodegradable polyesters • Longer chain C6 esters desirable for compatibility • Do not impact plastic properties at typical additive loadings • Provide stabilising role  reduce oxidative and UV-induced degradation  Similar to bark on a tree • PLA & Tannin esters • C6 ester chains lower Tg onset up to 5-6C • Can reduce flexural properties by 15% (TanAc to Hex) • C6 esters retain PLA flexural properties on aging Overall • Scope for tannin esters as sustainable additives for bioplastics

19. Acknowledgements • This work was supported by Biopolymer Network Ltd • Funding through New Zealand Ministry of Business, Innovation and Employment. • Jamie Bridson, Cole Lomas and Jaime Elliot are grateful for studentships provided by Scion through BSc(Tech) placements with the University of Waikato (NZ) • Carmen Schrade (MSc thesis) is grateful to assistance provided by Department of Applied Chemistry, Reutlingen University (Germany)

22. Plastic Polymer Properties • DMTA → 10% TanHex/TanHexAc lower PLA Tg • Lower ester quantity or shorter chain length → reduced effected • DSC → melt temperature unchanged • Crystallization decreased with tannin ester content Crystallisation Tg • At typical additive content minimal impact on polymer properties

23. Accelerated Aging • Biopol samples show similar increases in flexural modulus • longer chain tannin esters still maintain relatively lower flexural modulus than pure • maintain flexural strength compared to pure polymer

24. Tannin Ester Modified Biopolyesters Microscopy: • Hexanoate C6 chains compatible polyester plastics Mechanical & Polymer Properties • Do not detrimentally impact mechanical properties at loadings up to 5% (w/w) • Do not significantly influence polyester melt or Tg • As plastic additives provide: • UV stability • Antioxidant and thermal stability  Dependency on ester chain length, DS and content

25. Tannin Ester Modified Biopolyesters • Tannin ester addition contributes colour • white/colourless preferred • brown colour → undesirable for some applications • ester modification reduces colour • Accelerated weathering revealed colour instability • surface bleaching by UV light • inherent property of tannins  biopolyesters unsuited to exterior conditions