Toughening Bioplastic Materials with Nanosprings for Improved Strength Qualities

Bryce Dinger

Renewable Materials Program, University of Idaho, Moscow ID 83844-1132

• Issues with Conventional Plastic

Environmental pollution both terrestrial and marine

• How to Overcome These Issues

Substitute non-degradable petrochemical based polymers

with bioplastics (biodegradable and/or bioderived plastics)

• Bioplastics

Good biodegradability qualities

Generate fuel by anaerobic digestion

Divert waste from landfills

Can contribute to healthier rural economies

Can be made from a variety of renewable resources

Introduction

Bioplastics and Nanosprings

3-hydroxybutyrate-co-3-

hydroxyvalerate (PHBV)

Problems with PHBV

1. Formation of large

spherulites

2. Low nucleation densities

3. Low toughness (brittle)

Tensile Tests

Spherulite MorphologyImages taken from hot-stage polarized light optical microscopy

DSC Curves

Conclusions

• It was found that nanosprings resulted in

higher nucleation densities allowing more

sites for crystal spherulites.

• Through tensile tests it was found that the

PHBV + 1% NS composites required more

energy to break (tougher) than PHBV

controls, whilst having a decreased average

tensile stress and modulus of elasticity.

• The spherulites morphology of PHBV + 1% NS

composites showed smaller, densely packed

spherulites increasing its strength properties

making it less likely for cracks to propagate.

Acknowledgments

• University of Idaho OUR program for financial

support

• Dr. Armando McDonald (Renewable Materials

Program) as a faculty mentor

• Dr. David Mcilroy (Physics Department) for

supplying the nanosprings

• Ms. Shupin Luo (visiting scholar from Beijing

Forestry University) for her technical help

PHBV

Sample Preparation via Compound &

Injection Molding

RESIN MATRIXNanosprings

Propagating crack

Crack stopped propagating

Silica-

Nanosprings

Carbon Cycle of PHBV

Plant derived raw material

Bacteria

Fermentation

PHA polymer

(granules)

Biodegradation

Photosynthesis

RECYCLED

• Biocomposites preparation:

Compound using a Dynisco lab

mixing extruder/molder (LMM)

Nanosprings (NS): 0.01 wt%

Processing temperature: 175 C

Processing time: 7 min

Sample injection molded into dog-

bone specimens

PHBV PHBV + 1% NS

PHBV + 1% NS PHBV

• PHBV pictured here show

large fractured spherulites

averaging 0.56 mm in

width.

• PHBV + 1% NS showed high

nucleation densities and much

smaller spherulites with an

average width of 0.16 mm.

• PHBV showed slightly higher average maximum tensile stress than PHBV +

1% NS. PHBV also had a significantly larger Modulus of Elasticity than

PHBV + 1% NS.• The PHBV + 1% NS showed a

higher average energy at

break. This is consistent with

the microscopy because the

denser nucleation sites allowed

for better coupling and a less

brittle sample than the control

(PHBV).

• Differential scanning calorimetry (DCS) tests showed that

addition of 1% NS reduced PHBV crystallinity from 64% to

59%. This was consistent with the microscopy findings since

the NS created a greater amount of nucleation sites and

thus formed smaller spherulites with lower crystalynity.

PHBV Heat Flow Diagram PHBV NS Heat Flow Diagram

PHBV NS

Carbon fibers

Carbon fibers

nanospringRESIN MATRIX

Interlayer

RESIN MATRIXNanosprings

Propagating crack

Crack stopped propagating