Jan 6 2004
Background
All forms of cellulose degrade before they melt but natural cellulose can be regenerated by the xanthate process to manufacture fibres, commonly called rayon or viscose, and film, commonly called by its earliest brand name Cellophane®.
The latter films are plasticised by glycols and water to overcome their brittleness and are transparent, colourless and of moderate crystallinity. They were very widely used for packaging but have been substantially replaced by synthetic thermoplastics, especially polypropylene.
Cellulose has very high permeability to moisture and, especially when dry, very low permeability to permanent gases. Their moisture content varies greatly with their environment reaching approximately 50% at 100% relative humidity.
Not surprisingly, this causes many of their properties to vary considerably - so summarised values must be treated with considerable caution.
Key Properties
The key properties of cellulose are tabulated below.
Table 1. Key Properties
| Chemical Resistance |
| Acids - dilute |
Good |
| Alkalis |
Good |
| Greases and Oils |
Good |
| Electrical Properties |
| Dielectric constant @1 MHz |
4 (dry) |
| Dielectric strength ( kV.mm-1 ) |
30-50 @ 1 mm |
| Dissipation factor @ 1 kHz |
0.06 |
| Volume resistivity ( Ohm.cm ) |
1010 - 1012 |
| Mechanical Properties |
| Elongation at break ( % ) |
18/55 |
| Tensile modulus ( GPa ) |
5/3 |
| Tensile strength ( MPa ) |
120/55 |
| Physical Properties |
| Density ( g.cm-3 ) |
1.44 |
| Limiting oxygen index ( % ) |
approx. 18 |
| Water absorption - equilibrium ( % ) |
50 |
| Thermal Properties |
| Specific heat ( J.K-1.kg-1 ) |
approx. 1400 |
| Properties Cellulose Film |
| Property |
|
Value |
| Extension to break - Longitudinal |
% |
18 |
| Extension to break - Transverse |
% |
55 |
| Permeability to Carbon Dioxide @ 25 °C |
x10-13 cm3.cm.cm-2.s-1.Pa-1 |
0.01 |
| Permeability to Hydrogen @ 25 °C |
x10-13 cm3.cm.cm-2.s-1.Pa-1 |
0.01 |
| Permeability to Nitrogen @ 25 °C |
x10-13 cm3.cm.cm-2.s-1.Pa-1 |
0.005 |
| Permeability to Oxygen @ 25 °C |
x10-13 cm3.cm.cm-2.s-1.Pa-1 |
0.005 |
| Permeability to Water @ 25 °C |
x10-13 cm3.cm.cm-2.s-1.Pa-1 |
>15,000 |
| Tensile modulus - Longitudinal |
GPa |
5 |
| Tensile modulus - Transverse |
GPa |
3 |
| Tensile strength - Longitudinal |
MPa |
120 |
| Tensile strength - Transverse |
MPa |
55 |
| Properties Cellulose Fibre |
| Property |
|
Value |
| Material |
|
Medium tenacity rayon |
| Specific Modulus |
cN/tex |
300 - 700 |
| Coefficient of thermal expansion |
x10-6 K-1 |
approx. 80 |
| Density |
g.cm-3 |
1.5 - 1.55 |
| Extension to break |
% |
20 - 40 |
| Tenacity |
cN/Tex |
13 - 23 |
| Thermal Conductivity @ 23 °C |
W.m-1.K-1 |
approx. 0.06 |
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