Ranji Vaidyanathan and Krishna Bastola

Next Generation Materials Lab (NGML), Helmerich Research Center, Oklahoma State University, Tulsa,

OK 74106

Synthesis of nanofiller derivatives as effective fillers for improved dispersion in creating

high performance composites

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Outline

❑ Background

❑ Objective

❑ Grafting reaction of Starch and POSS

❑ Selective toughening of composites with grafted

nanofillers

❑ Characterization and Results

❑ Applications

❑ Conclusions

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Delamination Issues

Mode I Delamination fracture

❑ Well known that delamination fracture between plies is a serious problem in composites

❑ Improved fracture toughness and interlaminar shear strength is desired 3

Techniques to Impede Delamination

❑ Interleaving is the insertion of a tough layer of material between prepreg plies

❑ Z-pinning is the insertion of rigid cured carbon fiber/BMI resin rods (Z-pins) into the laid up uncured plies

❑ Stitching the prepregs can effectively impede delamination

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Issues with Traditional Methods❑ Z-pinning –

• Only applied to prepreg type materials • Tremendous loss of in-plane properties

❑ Stitching – • Fracture toughness improved at the

sacrifice of in plane mechanical properties

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Dimensionalities in nanoparticles

❑ Surface areas

❑ Reactivity

❑ Strength

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❑ Nanoclay ❑ Carbon nanotubes ❑ Graphite nanoparticles (GNP) ❑ Graphene and Graphene oxide ❑ Nano silica ❑ Polyhedral Oligomeric Silsesquioxane (POSS) ❑ POSS grafted natural polymers or PGP

Nanoparticles for Interlaminar Modification

Nano-additives are incorporated in the matrix for improved interlaminar fracture toughness

Graphene oxide and POSS interlaminar modification

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Previous work with Nanofillers

❑ Addition of nanofillers drastically improves the mechanical and physical properties of composites

➢ Dispersed in a polymer carrier – Polyvinyl pyrrolidone➢ Improved interlaminar fracture toughness by ~100% or

more➢ Improvement over reported values for CNT at much

lower nanofiller contents ❑ Types of nanoparticles:

➢ Graphene oxide ➢ Different polyhedral oligomeric silsequioxane (POSS) ➢ Different number of reactive groups

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Previous work with GO Nanofillers

Average Fracture energy of modified carbon fiber composites

• 5% GI and 5% GO composites gave maximum GIC values

• 5% GO composites showed more than 100% mode 1 fracture improvement

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References Nanoparticles A p p l i c a t i o n method

% N a n o p a r t i c l e content as a function of the composite

Mode I GIC

improvements

Scalableto industrial process

Kostopoulos CNF Casting 1 vol.% 100% YesJiang et al. Fullerene Casting 2 wt% of matrix 30-40% Yes

Thakre et al. Functionalized and pristine

SWNTs

Spray 0.01 wt% 7 and 9%

Yes

Wicks et al. CVD grown Carbon

nanotubes (CNTs)

Chemical vapor deposition

1-2% (Volume fraction) 76% No

Garcia et al. CVD grown CNTs

Layer of CNT removed from a substrate and rolled onto the prepreg

1% volume fraction 150% No

Arai et al. Vapor grown carbon fibers

and vapor grown carbon

nanofibers

Coated with a metal roller

20 g/m2 50% Yes

Graphene oxide

Graphene oxide

Painted, sprayed or rolled on prepreg or

0.01 wt% or 2.7 E-04 g/m2

~100% Yes

Comparison with other researchers

Effect of Nanofillers and their dispersion

❑ The effect of nanofillers depend on: ➢ Effective dispersion ➢ Interaction with the matrix (nanoparticle reactivity)

❑ Presence of polymer carrier ➢ No improvement without polymer carrier (possible

hydrogen bonding and interaction between nanoparticles and matrix resin mediated by the carrier)

➢ Polymer carrier alone reduces the modulus ➢ Addition of nanoparticles recovers modulus ➢ Nanoparticle agglomeration beyond a certain value

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 Polyhedral silsesquioxane (POSS)

One or more reactive functional groups suitable for polymerization and grafting

Unreactive organic R group for Compatibility and solubility in polymer

• 1-3 nm sized nanomaterial with inorganic silica cage and organic hydrocarbon branches

• Thermally and chemically robust inorganic–organic hybrid nanomaterial

• A promising nanofiller for reinforcing polymer coils at molecular level

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Objective

❑ Graft POSS molecule onto a natural polymer ➢ Increase nanoparticle loading levels ➢ Increase the dispersion at high loading ➢ Eliminate issues related to agglomeration

❑ Use of natural polymer for developing synthesis of grafted nanofiller

❑ Test the grafted molecule as an effective nanofiller

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Structure of Starch

(a) = Amylopectin (b) = Amylose

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Grafting of POSS and amyclopectin

1) Solvent 2) Aluminium triflate 3) Reflux

+

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IR characterization of POSS grafted molecule

❑ Epoxy group detected at 912 cm-1 ❑ The bands are absent in amylopectin and

grafted molecule17

Test of POSS grafted molecule as an effective filler

❑ The filler was coated on the interlaminar surface of carbon fiber

❑ Mode 1 fracture toughness was measured

❑ Epoxy composite containing grafted nanofiller was fabricated

❑ DMA and flexural tests were conducted

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❑    Solid disperser, carrier and stabilizer for nanoparticles❑ Compatibilizer for resin systems

Dispersion of grafted nanoparticles

Polyvinylpyrrolidone (PVP-K90)

5% alcoholic solution of PVP-K90 + grafted nanomaterial (different wt% of @PVP) (2, 3, 7 and 10)

Magnetically Stirred for 10 minutes

Nanomaterial dispersion

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Fabrication process

Carbon fiber prepreg Teflon sheet Spray or paint with PVP/nanofillers

carbon fiber laminates Coated with nanofillers in the mid plane and cured in hot press

Cut into stripes (200 mm x 25 mm)

Hinges glued

DCB test

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Fabrication process

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Fabrication process

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Calculation of wt% nanofiller @ of composite

0.15 x 20 x 2.54 cm D = 1.3 g/ cm3

Weight = 7.62 g 10 wt % of nanofiller @PVP = 0.5 gram in 100 ml = 0.05 gram in 10 ml

❑ Roughly 3 ml of solution was used =0.015 gram of nanofiller

❑ 0.2 wt % of nanofiller was used as a weight function of composite for the maximum content

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GIC is the mode I fracture toughness (J/m2)

P is the load (N)

δ is the load point displacement (mm)

b is the width of the specimen (mm)

a is the delamination length (mm)

Δ is the correction factor for MBT

Gic =3*P*δ

2*b*(a+ Δ )

Fracture toughness calculations

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Plot of load versus crack growth

• Crack growth is not continuous, but a sequence of growth and arrests

• Crack arresting tendency drastically improved for 7% and 10% grafted nanomaterial composites

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Interlaminar fracture toughness improvement

❑ 7% and 10% grafted nano filler (GN) composites showed maximum GIC values ❑ 10% GN composites showed ~ 100% mode 1 fracture improvement ❑ Unlike GO and POSS, maximum improvement has not been reached

Nor

mal

ized

Mod

e 1

frac

ture

ene

rgy,

J/m

2

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Significant Results

❑ Interlaminar fracture toughness increases with grafted nanofiller (GN) content

❑ Effect not significant at lower GN contents

❑ ~10 wt% GI POSS gave best improvement in fracture toughness (~ 100%)

❑ The saturation loading point yet to be determined, but expected to be around 30% - compared to 5-7% for other nanofillers

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Proposed mechanisms of toughness improvement: Increasing the length of the crack

❑ Crack deflection – twisting and tilting the crack

❑ Crack pinning❑ Plastic flow

Mechanisms

Nanomaterial Resin PVP

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5 wt% Graphene Oxide0 wt% Graphene Oxide

!  Smooth fracture surface of 0 wt% GO – low crack resistance

!  Rough fracture surface for 5 wt% GO – high crack resistance

Fracture Surface Morphology

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5 wt% Graphene Oxide

! A lot of twisting and tilting on the fracture surface

! Different planes perpendicular to fracture surface

Possible Crack Pinning

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10% GI POSS

! Good fiber-matrix bonding

! River pattern – plastic flow (higher fracture energy)

! POSS aggregation! Matrix failure! Good fiber – matrix

bonding

5 % GI POSS

Fracture Surface Morphology (POSS)

Storage modulus of GN-epoxy composite

• Storage modulus significantly increased (doubled) with the addition of GN

• Tg is increased by 20°C

control2%

Temperature  °C  

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DMA of 3% GN-epxy composite

• Tg increased by 20°C with the incorporation of GN • Storage modulus increased by three times with 3%

GN

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Flexural yield strength of GN epoxy composite

❑ The yield strength slightly decreased compared to control sample

❑ Effect on yield strength at higher percent loading to be determined

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Flexural modulus of GN-epoxy composite

5 % GI POSS

❑ Flexural modulus similar to control sample ❑ Expected to be similar for higher percentages

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• High pressure tanks for CNG storage• Low pressure tanks for natural gas storage• Nanofillers help in improved impact

resistance• Poor dispersion will lead to poor impact

properties

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Applications in All-Composite containers for CNG

How can composites be used in fuel tanks?

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• Design to mitigate effect of degradation by exposure to multiple operating environments

• Reduced permeability and damage tolerance • chemical exposure, low temperatures, and high

internal pressures• must be compatible with and easily adaptable to • currently qualified materials and fabrication

techniques

CNG Tank Evolution

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Significant Results

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•  A final tank design was successfully manufactured and tested. The tank weighs 33% lighter than a typical type III tank. The tank passed D.O.T. certification through an 18,000 cycles test, a hydrostatic burst test, and 2 bonfire tests.

Tank Specifications•  Weight: 180lbs•  Dia. 23.5”

•  Length 62”

•  Capacity 27 gge•  Working Pressure 4500 psi

•  Burst Pressure 12,010 psi

Conclusions❑ New grafted nanomaterial synthesized

− The grafted nanomaterial readily dispersible in organic

solvents (acetone, ethanol etc.)

− Can be dispersed with or without a PVP carrier

− Possible as film, spray or paint (spray or paint

preferred)

❑ Grafting process can be extended to other naturally

available polymers

❑ Mode 1 fracture toughness improved by ~100% due to

crack pinning and crack deflection

❑ Storage modulus improved by 3 times 40

ACKNOWLEDGEMENTS

❑ Varnadow Endowed Chair funds from the Walter Helmerich Family, Tulsa, OK

❑ Zachary Carpenter, Research Engineer, Manager, Helmerich Research Center, and Richard S. Claunch, CEAT Lab, OSU, Tulsa

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Helmerich Advanced Technology Research Center (HATRC)

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Helmerich ATRC at OSU-Tulsa$51.9 million, 123,000 sq. foot building40 faculty and 100 graduate students

Four strategic areas with focus on advanced materialsOpened doors on November 29th, 2007http://www.osu-tulsa.okstate.edu/atrc/

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Focus on Materials Processing and Characterization

MaterialsLow cost processing

Application specific

properties

Advanced Materials/

Nanomaterials

Energy MaterialsSustainability/

Recycling

Biomaterials