Polyhydroxyalkanoates (PHA, PHB)

The material. PHAs are linear polyesters produced in nature by bacterial fermentation of sugar or lipids derived from soybean oil, corn oil, or palm oil. They are fully biodegradable. More than 100 different monomers can be combined within this family to give materials with a wide range of prop­erties, from stiff and brittle thermoplastics to flexible elastomers. The most common type of PHA is PHB (poly-3-hydroxybutyrate), with properties similar to those of PP though it is stiffer and more brittle. The following data is for PHB.

Composition

(CH(CHs)—CH2—CO—O)n General properties

Density

1230

– 1250

kg/m3

Price

3.2

– 4

USD/kg

Mechanical properties

Young’s modulus

0.8

– 4

GPa

Yield strength (elastic limit)

35

– 40

MPa

Tensile strength

35

– 40

MPa

Compressive strength

*40

– 45

MPa

Elongation

6

– 25

%

Hardness—Vickers

*11

– 13

HV

Fatigue strength at 107 cycles

*12

– 17

MPa

Fracture toughness

*0.7

– 1.2

MPa. m1/2

Thermal properties

Melting point

115

– 175

°C

Glass temperature

4

– 15

°C

Maximum service temperature

*60

– 80

°C

Thermal conductor or insulator?

Good insulator

Thermal conductivity

*0.13

– 0.23

W/m. K

Specific heat capacity

*1400

– 1600

J/kg. K

Thermal expansion coefficient

*180

– 240

p, strain/°C

Electrical properties

Electrical conductor or insulator?

Good insulator

Electrical resistivity

*1 X 1016

– 1X 1018

pnhm. cm

Dielectric constant

*3

– 5

Dissipation factor

*0.05

– 0.15

Dielectric strength

12

– 16 106

V/m

PHB containers. (Kumar and Minocha, Trangenic Plant Research, Harwood Publishers.)

Ecoproperties: material

Embodied energy, primary production

50

– 59

MJ/kg

CO2 footprint, primary production

*2.25

– 2.66

kg/kg

Water usage

*100

– 300

l/kg

Ecoproperties: processing

Polymer molding energy

*8.24

– 9.09

MJ/kg

Polymer molding CO2

*0.65

– 0.72

kg/kg

Polymer extrusion energy

*3.21

– 3.54

MJ/kg

Polymer extrusion CO2

*0.25

– 0.28

kg/kg

Recycling

Embodied energy, recycling

21

– 24.8

MJ/kg

CO2 footprint, recycling

*0.94

– 1.12

kg/kg

Recycle fraction in current supply

0.5

– 1

%

Recycle mark

Other

Typical uses. Packaging, containers, bottles.