greening plastics: modifying plastics with functional additives based on condensed tannin esters...

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

    Warren GrigsbyJamie Bridson, Cole Lomas Carmen Schrade and Jaime-Anne [email protected]

  • Overview Highlights of a greater study evaluating tannin esters in plastics

    IntroductionTannins & plastic additives

    Tannin esters in plastics Filler v compatible, active ingredientProviding functional equivalenceSpecific performance

  • Introduction: Condensed TanninsNature provides a range of condensed tanninsLeaf, fruit, stem and bark

    Provide a protection role for plant/treeSecondary metabolitesPolyphenolic structureExtractableProcyanidin: flavonoid base structuren

  • Tannins: Providing Function Blueberries, bark, wine, antioxidant, protein inhibition, UV absorption

    Neutriceuticals, food, industrialoxidative stress-cognitive functionprotein inhibitionantimicrobialtanning leather

  • Plastic Additives: Adding PerformanceAdditives provide functionality and longevitycolour, flame retardant, plasticizers

    Longevityantioxidants and UV stabilisersnot so well knownsynthetic, petrochemicalBHT, hindered amines

    Why not bio?

  • Tannin usually a crosslinked molecule in adhesivesPhenol formaldehyde, Bakelite chemistry

    PLA plastic modified with tanninsreinforcement, melt-spun filaments

    Electrospinning protein nanofibrestannin functionality

    Tannins: Synthetics & PlasticsGrigsby, Kadla, Macromolecular Materials and Engineering, 299(3) 2013 368378. Dallmeyer, Grigsby, Kadla, J Wood Chem Tech 33(3) (2013) 197-207. 10mm10mm

  • Aims & GoalsCan functionality a tree uses be applied to plastics?

    HypothesisTannin efficacy in bark can be applied to protect plastics from oxidative aging and UV-induced degradation

    Evaluate tannins as bio-sourced plastic additives

  • Tannins: water soluble extracts inherently hydrophilicModify change miscibility/compatibility with plasticsTannins & Chemical ModificationTannin+Alkyl Anhydride

    Tannin EstersC2C6 chain lengthMixed Esters

    Vary:Degree of substitution (DS)Antioxidant CapacityMacromolecular propertiesUV absorptionR1,2 = Ac, Pr, Bu, HexGrigsby, et al. Polymers, 2013, 5(2), 344-360

  • Tannins: water soluble extracts inherently hydrophilicModify change miscibility/compatibility with plasticsTannins & Chemical ModificationTannin+Alkyl Anhydride

    Tannin EstersC2C6 chain lengthMixed Esters

    Vary:Degree of substitution (DS)Antioxidant CapacityMacromolecular propertiesUV absorption

  • Plastic Processing & EvaluationTannin esters compounded in plastics 0-10% w/wMaster Batch

    Tannin Ester (10%) compounded with plastic

    PP, PBS PLA, PHA, PHBExtrusion

    MB blended with plastic

    0%, 0.5%, 1%, 3%, & 5%, 10%Injection Moulded

    ASTM Test specimens

    Flexural & Tensile bars

    Thermal AnalysisDSC, TGA, DMTAMechanical TestingFlex & TensileAccelerated AgingThermallyUV & weathering Fluorescence & lightmicroscopy

  • 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 TanPrTanBu TanHex(image 500 x 500 m)Confocal microscopy: PLA containing 5% tannin esters using tannin inherent autofluorescenceGrigsby, et al. Polymers, 2013, 5(2), 344-360

  • Plastic Additive or Filler?Tannin esters contribute up to 15% decreased PLA stiffness ester chain length & greater content decrease MOEnative tannin stiffens PLA acts as a fillerNative TanninTanAcC2 EsterLongerChain C6 EstersShort Chain C3-C4 Esters

  • Plastic Polymer Properties10% C6 esters lower PLA Tgreduced effectlower ester quantityshorter chain lengthAt typical additive content minimal impact on polymer propertiesTgCrystallisationCrystallization decreased melt temp. unchanged


  • Thermal & Oxidative StabilityTannin esters promote plastic thermal stabilityOxidation induction time (OIT)TanHex in PP increased OIT, TanHexAc not

    residual antioxidant capacity importantIncreased thermal stabilityReprocessed PP (up to 10x) reduced thermal stability

    10% TanHex increase thermal stability

    potential to lower plastic oxidative degradation on processingTGAGrigsby, et al., Macromolecular Materials and Engineering, 299 (10) (2014)12511258.

  • Plastic Accelerated AgingTannin esters provide UV stability on aging polypropylenebiopolyesters challenged by agingNative TanninMixed C2-C6 EstersLongerChain C6 EsterMechanical properties before/after UV and condensation exposure cycling

  • Accelerated AgingBionolle (PBS) samples increase in stiffnesstannin hexanoate ester excellent flexural strength retentionsimilar results on thermal aging

    Functional equivalency comparable to commercial UV stabilisersNative TanninMixed C2-C6 EstersLongerChain C6 EsterGrigsby et al, J. Appl. Polym. Sci., 132(11) (2014) 41626

  • Accelerated Aging plastic colour tended to surface bleachseen as undesirable, but gauge for tannin efficacy

    Measure efficacyColour Stability and UV inhibitionVisiblebleaching0.24 mmIntensity acrossthe surfaceTannin sacrificial bleach depth extent of UV inhibitionPBS: TanHex 0.25 mm v. TanAc 0.47 mmconsistent with tannin dispersion by microscopyGrigsby et al, J. Appl. Polym. Sci., 132(11) (2014) 41626White Intensity

  • Take home informationTannin esters can be functional additives in biodegradable polyestersLonger 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 estersC6 ester chains lower Tg onset up to 5-6CCan reduce flexural properties by 15% (TanAc to Hex)C6 esters retain PLA flexural properties on aging

    OverallScope for tannin esters as sustainable additives for bioplastics

  • AcknowledgementsThis work was supported by Biopolymer Network LtdFunding 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)

  • Plastic Polymer PropertiesDMTA 10% TanHex/TanHexAc lower PLA TgLower ester quantity or shorter chain length reduced effected

    DSC melt temperature unchanged Crystallization decreased with tannin ester contentAt typical additive content minimal impact on polymer propertiesTgCrystallisation

  • Accelerated AgingBiopol samples show similar increases in flexural moduluslonger chain tannin esters still maintain relatively lower flexural modulus than pure maintain flexural strength compared to pure polymer

  • Tannin Ester Modified BiopolyestersMicroscopy: Hexanoate C6 chains compatible polyester plastics

    Mechanical & Polymer PropertiesDo 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 stabilityAntioxidant and thermal stability Dependency on ester chain length, DS and content

  • Tannin Ester Modified BiopolyestersTannin ester addition contributes colourwhite/colourless preferredbrown colour undesirable for some applicationsester modification reduces colour

    Accelerated weathering revealed colour instabilitysurface bleaching by UV lightinherent property of tannins biopolyesters unsuited to exterior conditions

    *native tannin stiffens PLA acts as a filler (like lignin)