Upgrading vegetable oil thermosets through co-polymer reinforcement with tannin-lipid conjugates

1. Upgrading vegetable oil thermosets through co-polymer reinforcement with tannin-lipid conjugates Warren Grigsby Chunhua Luo, Neil Edmonds, Jafar Al-Hakkak warren.grigsby@scionresearch.com

2. Overview: Unsaturated Copolymer Thermosets Polyester Resins Petrochemical-based Maleic anhydride Bisphenol A Styrene Divinyl benzene Unsat. Oil Systems Partial replacement Vegetable oils Styrene Divinyl benzene - req for cross-linking Unsat. Oil Systems Totally bio-based Vegetable oils Polyphenols - assist cross-linking

3. Introduction • Thermoset resins → performance materials • polyesters and epoxies  renewables substitution? • A major challenge with feedstock replacement is performance • strength and durability • automotive and construction applications • Natural oils investigated as raw materials for thermoset resins and co-polymers • readily available, potential bio-degradability and multi-functionality • differing fatty acid composition and unsaturation → ideal feedstocks Meier, Metzger, Schubert, Chem. Soc. Rev., 2007. 36(11): p. 1788-1802.

4. Natural Oil Thermosets • Thermosets prepared via unsaturation or introduced functional groups • radical, condensation, oxidative polymerization • High degree of unsaturation for reactivity • thermal or cationic polymerization • Natural oils need co-monomers • styrene or divinyl benzene for performance Larock et al., Polymer, 2000. 42(4): p. 1567-1579; Biomacromolecules, 2005. 6(2): p. 797-806.

5. Condensed Tannins • Nature provides a range of condensed tannins • Leaf, fruit, stem and bark • Polyphenolic, flavanyl sub-unit • Tannin usually a cross-linked molecule in adhesives • Phenol formaldehyde, Bakelite chemistry • Structural applications requiring durability, strength • Provide reinforcement in modified PLA plastics

6. Condensed Tannins • Tannins are oligomeric polyphenolics • typically n = 4 to 13 • Possess rigid aromatic structures • Easily functionalised – esters, ethers • Potential to substitute petroleum-based co-monomers in natural oil-based co-polymer formulations  Thermoset completely composed of renewable resources n

7. Aims • Produce a totally biobased thermoset resin • based on vegetable oils and tannins • Utilise flavanyl structure → rigidity & cross-linking networks Evaluate • differing tannin types, content and fatty acid ester DS • natural oils with varying unsaturation & reactivity

8. Conjugating fatty acids by esterification • Tannin Linoleate and Oleate esters formed • differing unsaturation → reactivity & cross-linking • Two tannin types • similar degree of substitution (DS = 2) • residual hydroxyls capped by acetate groups -CH2- -CH3 X HC= -COCH3 Pine Tannin ArH X Quebracho Tannin Luo, Grigsby, Edmonds, Al-Hakkak ActaBiomaterialia 9 (2013) 5226–5233.

9. Co-polymerization with vegetable oils • Used different methods for radical polymerization • Co/Zr oxidative catalyst • Range of tannin ester contents (PTLA 0→100%) • Linseed and tung oils • Solvent cast films = hard, rigid → soft, flexible • Monitor co-polymerization • loss of unsaturation • auto-oxidation

10. Chemical analysis of co-polymer films • Cast films evaluated by 13C NMR and solvent extraction • Esterification retained • Decrease of C=C Co-polymer film Tannin Linoleate Tannin

11. Co-polymer material properties DMTA • Comparable to typical polyester thermosets • PTLA has greater film stiffness (E’) • Pure oil least  Lower tannin ester content contributes to decreasing E’ and at lower temperatures Pine Quebracho

12. Co-polymer material properties Tan d profiles • Higher Tg with tannin ester content → greater cross-linking • Quebracho tannin Tg 32 to 64˚C • Pine tannin Tg 36 to 72 ˚C • Higher tannin → peak intensity decrease, over a broader range Pine Quebracho

13. Co-polymer cross-link density • Kinetic theory of rubber elasticity → cross-linking density • E’ values taken 20˚C above Tg  Cross-link density increase with tannin ester content Co-polymer Tannin E25°C νe103 Tg (%) (GPa) (mol/m3) (C) QTLA100281.324 64 PTLA100321.65872 PTLA75-LIN25 241.32356 PTLA50-LIN50160.71043 PTLA25-LIN7580.1138 LIN10000.010.0824 Luo, Grigsby, Edmonds, Al-Hakkak ActaBiomaterialia 9 (2013) 5226–5233

14. What happens if we change oil/conjugate ? Tannin Oleate esters or lower oil unsaturation  Slower reaction • undertake at 60˚C, require post-cure at 100˚C • Soft-flexible films • more oil, greater flexibility

15. What happens if we change oil/conjugate ? Tannin Oleate esters or lower oil unsaturation • Slower reaction • Soft-flexible films • more oil, greater flexibility Pine Quebracho • More oil → stepwise decrease in softening onset • Tg’s typically 9-13˚C • Second broader increase >50˚C • post-curing, second Tg  2-phase system Luo, Grigsby, Edmonds, Al-Hakkak Macromolecular Materials and Engineering, 2014, 299(1) pp 65–74.

16. Summary • Tannin fatty acid esters and vegetable oils give varyingco-polymerization rates and material properties • Tannin esters provide additional cross-linking sites for co-polymerization beyond the triglyceride

17. Summary • Tannin fatty acid esters and vegetable oils give varying co-polymerization rates and material properties • Tannin esters provide additional cross-linking sites for co-polymerization beyond the triglyceride Tannin Linoleates • Linoleates give greater range in properties and Tg’s • Dependent on tannin ester content • Single Tg → single co-polymer phase and homogeneity in films • Tannin linoleates and oils have similar polymerization rates and cross-linking • not case in analogous vegetable oil – styrene/divinyl benzene

18. Summary • Tannin fatty acid esters and vegetable oils give varying co-polymerization rates and material properties • Tannin esters provide additional cross-linking sites for co-polymerization beyond the triglyceride Tannin Oleates • Introducing lower unsaturation reduces reactivity • 20-40 times slower • Tannin oleates give rubber-like materials • reduced cross-linking with 1-2 Tg features • Offer differing dampening properties → rubbers with relatively rigid domains

19. Conclusions • Tannin fatty acid conjugates can replace styrene and divinyl benzene in vegetable oil co-polymers • Tuning reactivity gives co-polymers ranging from soft rubbers to hard thermosets • Lineolate esters and >20% tannin content give co-polymer properties reported for styrene-vegetable oil systems  Using tannin conjugates realizes a totally bio-based co-polymer thermoset

20. Acknowledgements • The work presented in this study was supported through funding provided through the New Zealand Ministry of Business, Innovation & Employment • C.L. thanks the Biopolymer Network Ltd for financial support and PhD scholarship stipend • This presentation is dedicated to the late Prof. Allan Easteal who was a supervisor, colleague and contributor to this work

22. Polymer Properties DSC • Thermograms exhibit exothermic peak >100˚C • Likely further thermal polymerization & post-cure • Higher oil content → broadens, lower temperature • Consistent with DMTA

23. What happens if we change oil/conjugate ? Tannin Oleate esters or lower oil unsaturation • Slower reaction • Soft-flexible films • more oil, greater flexibility Co-polymer Tannin E25°C νe103 Tg (%) (GPa) (mol/m3) (C) PTLA100321.65872 PTOA100250.3---- PTLA75-LIN25 241.32356 PTOA75-LIN25190.5937 PTOA75-TUN25 190.889