Processing Characterization of Bio-Plastics Yanir Shaked

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Yanir Shaked

University of Massachusetts, Lowell

Shenkar College of Engineering and Design

Green Plastics Technology

June 08

Processing and Characterization

of Bio-Plastics

Thursday, June 26, 2008

http://www.shenkar.ac.il/

http://www.shenkar.ac.il/

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• Bio-Plastics are not a single class of polymers but rather a family of products which can vary considerably

• A generally recognized definition of the concept does not exist

• Bio-Plastics consist of– Biobased plastics, based on renewable resources

– Biodegradable polymers, which meet all criteria of scientifically recognized norms for biodegradability and compostability

Introduction


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• Slow Recrystallization• Moisture absorption

– Hydrolytical degradation, mainly PLA above Tg– Bulk imperfections for PHA

• Thermal degradation– Mw reduction affecting Melt strength, Mechanical

properties

• Viscosity– Melt elasticity of linear polyesters

• Foaming, Thermoforming, Blown Film, Blow Molding

– Shear thinning effects, coupled with Mw reduction

Bio-Plastics’ Properties


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• Implications– Drying

– Increased cycle time, lower line speeds (compare to polyolefines)

– Low processing temperatures, many times at relatively high viscosity

• High Pressure, and Torque requirements

– Tools’ design for reduced viscous heating and residence time

Processing Considerations


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Processing of Bio-Plastics

Nature Works, Jim Nangeroni, 2007Thursday, June 26, 2008

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Telles, Robert S Whitehouse, 2007


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• Poly Hydroxybutyrate, PHB, is the most common of PHA

• Bio-Based and Bio-Degradable Polymer

• Aliphatic, thermoplastic, linear, semi-crystalline polyester

• When copolymerized can cover a wide range of mechanical properties

Poly Hydroxybutyrate

0.5µm

K. Sudesh et al, 2000Thursday, June 26, 2008

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PHB, Melt CharacteristicsDSC

PP2300c


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Parallel Plate Rheology

Slope:-2.601X10-4

Slope: -1.516X10-3

@ 300sec (5min), 26% reduction in Mw @ 1850c 5% reduction in Mw @ 1650c

165oc185oc

PHB, Melt Characteristics


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Rheological Characterization

• Tm – 1700c

• Capillary Rheometer @ 1800C

• 27% MW loss

J. Zhang, et al, 2004


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DSC

700c

PHB, Melt Characteristics


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PHB, Processing

• Super cooling

• Processing below Tm

• Reverse Temperature Profile

J. Zhang, et al, 2004


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PHB, Processing

• Implement

– Characterization

– ProcessingT3 T2 T1


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• Extrusion Rheology

– True steady state

– Separate variables

• Viscous heating – Screw RPM and Design

• Residence time – Screw RPM and Design

• Temperature – Extruder and Die temperature profiles

– Extensive super-cooling

PHB, Extrusion Rheology


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• Apparent shear rate from flow rate

• Apparent shear stress from ΔP

• Apparent viscosity

H=1.5mmW=32mm

L=70mm

ΔP


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500

1000

1500

20 70 120

Pa*s

ec

Sec-1

160 172

Flow Curve


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Die melt temperature, different extruder temperatures

165

170

175

170 180 190

Die

mel

t T [0

C]

zone 3 set point [0C]


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Mw as a function of die set point, different RPM

160 170 180

Mw

Die setpoint 0C

30 50 40


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Extruder Melt temperature as a Function of RPM, different Temp. Set Point

190

195

200

205

210

30 40 50

Mel

t T [0

C]

RPM

171c 177c 182c


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Mw as a function of Melt temperature,

190 195 200 205 210

Mw

Melt T [0C]

30 40 50


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Parallel plate Rheology, as a function of

500

800

1100

1400

1700

30 40 50 60 70

Pa*

sec

RPM

CR=3.5, T3=166c CR=3, T3=154c


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Extrusion well below Tm

120

135

150

165

180

120 135 150 165 180

Die

mel

t T [0

C]

Die set point [0C]


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Conclusions

• Extrusion Rheology is a very powerful tool for the determination of PHB flow characteristics, and possibly other thermally unstable Bio-Plastics

• Residence time effects overwhelm temperature effect, for the evaluated range

• Super cooling of the melt is possible up to 1350c, ~350c below Tm

• Best MW retention achieved at low temperatures, short residence times, and low shear


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Conclusions

• While as solid PHB resembles the behavior of other known polymers, its melt state differs substantially

• Loss in molecular weight during processing should be taken into account

• There will always be some reduction in MW down the process stream

• Knowing the polymer’s limitations will ease its implementation into existing processes

• The use of Bio-Plastics in large scale manufacturing is doable


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Questions


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Processing Characterization of Bio-Plastics Yanir Shaked