Greening Plastics: Modifying plastics with functional additives based on condensed
tannin esters
Warren GrigsbyJamie Bridson, Cole Lomas Carmen Schrade and Jaime-Anne Elliot
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
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
Procyanidin: flavonoid base structure
OHO
OH
OH
H(OH)
OH
OHn
Tannins: Providing Function
Blueberries, bark, wine,… antioxidant, protein inhibition, UV absorption
Neutriceuticals, food, industrial oxidative stress-cognitive function protein inhibition antimicrobial tanning leather
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?
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
Tannins: Synthetics & Plastics
Grigsby, Kadla, Macromolecular Materials and Engineering, 299(3) 2013 368–378. Dallmeyer, Grigsby, Kadla, J Wood Chem Tech 33(3) (2013) 197-207.
10m
10m
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
Tannins: water soluble extracts → inherently hydrophilic Modify → change miscibility/compatibility with plastics
Tannins & Chemical Modification
Tannin+
Alkyl Anhydride
Tannin EstersC2–C6 chain length
Mixed Esters
Vary:Degree of substitution (DS)
Antioxidant CapacityMacromolecular properties
UV absorption
OR1O
R2
OR1
H(OR 2)
OR2
OR2 R1,2 = Ac, Pr, Bu, Hex…
Grigsby, et al. Polymers, 2013, 5(2), 344-360
Tannins: water soluble extracts → inherently hydrophilic Modify → change miscibility/compatibility with plastics
Tannins & Chemical Modification
Tannin+
Alkyl Anhydride
Tannin EstersC2–C6 chain length
Mixed Esters
Vary:Degree of substitution (DS)
Antioxidant CapacityMacromolecular properties
UV absorption
OR1O
R2
OR1
H(OR 2)
OR2
OR2
250 300 350 400 450
Abs
orba
nce
Wavelength (nm)
Vary UV absorption
Change meltbehaviour
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
Extrusion
MB blended with plastic
0%, 0.5%, 1%, 3%,
& 5%, 10%
Injection Moulded
ASTM Test specimens
Flexural & Tensile bars
Thermal AnalysisDSC, TGA, DMTA
Mechanical TestingFlex & Tensile
Accelerated 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 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
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
Native Tannin
TanAcC2
EsterLongerChain
C6 Esters
Short Chain C3-C4 Esters
Plastic Polymer Properties
10% C6 esters lower PLA Tg reduced effect
lower ester quantity shorter chain length
At typical additive content minimal impact on polymer properties
TgCrystallisation
Crystallization decreased melt temp. unchanged
Melt
DSCDMTA
Thermal & Oxidative Stability Tannin esters promote plastic thermal stability
Oxidation induction time (OIT) TanHex in PP → increased OIT, TanHexAc → not
residual antioxidant capacity important
Increased thermal stability
Reprocessed PP (up to 10x)→ reduced thermal stability
10% TanHex → increase thermal stability
potential to lower plastic oxidative degradation on processing
TGA
Grigsby, et al., Macromolecular Materials and Engineering, 299 (10) (2014)1251–1258.
Plastic Accelerated Aging Tannin esters provide UV stability on aging polypropylene
biopolyesters challenged by aging
Native Tannin Mixed
C2-C6 Esters
LongerChain
C6 Ester
Mechanical properties before/after UV and condensation exposure cycling
Accelerated Aging Bionolle (PBS) samples increase in stiffness
tannin hexanoate ester → excellent flexural strength retention similar results on thermal aging
Functional equivalency comparable to commercial UV stabilisers
Native Tannin Mixed
C2-C6 Esters
LongerChain
C6 Ester
Grigsby et al, J. Appl. Polym. Sci., 132(11) (2014) 41626
Accelerated Aging → plastic colour tended to surface bleach seen as undesirable, but gauge for tannin efficacy
Measure efficacy
Colour Stability and UV inhibition
0.00
50.00
100.00
150.00
200.00
250.00
0.50 1.00 1.50 2.00 2.50 3.00
Distance in mm
Inte
nsi
tyVisible
bleaching0.24 mm
Intensity across
the surface
Tannin sacrificial bleach depth → extent of UV inhibition PBS: TanHex 0.25 mm v. TanAc 0.47 mm
consistent with tannin dispersion by microscopy
Grigsby et al, J. Appl. Polym. Sci., 132(11) (2014) 41626
Whit
e In
tensi
ty
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 5-6C 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
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)
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
At typical additive content minimal impact on polymer properties
TgCrystallisation
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
Tannin Ester Modified Biopolyesters
Microscopy: 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 stability Antioxidant and thermal stability
Dependency on ester chain length, DS and content
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