Stiffness properties

Question 1

Name some stiffness measurements

Answer 1

Bending stiffness can be measured via static or dynamic methods
static - 2 point - sample clamped and forced to deflect by a point force used is measured
Resonance - Paper clamped at one end and a constant frequency applied the length exposed is then changed when it starts to vibrate the length is recorded

Question 2

What is the difference between tensile stiffness and bending stiffness

Answer 2

tensile - materials resistance to deforming under tension. Determined by claculation from tensile graph
Bending - resistance to bending forces

Question 3

What factors affect bending stiffness?

Answer 3

The modulus of elasticity. The filler content decreases stiffness
Fibre length very important
THICKNESS
calandering decreases

Question 4

How is tensile stiffness different to emodulus?

Answer 4

It is a property of the sheet and will change with grammage whereas e modulus should stay the same it is a property of the material

Question 5

What factors affect the stiffness of the paper ?

Answer 5

Very dependent on fibre orientation - MD much higher as fibres in alignment
Fibre length long fibres more flexible and more hydrogen bonds formed
Reduction in filler content as these disrupt H bonds
More compression of sheet decreases bending stiffness as reducing the voids in the sheet
MOST EFFECTIVE IS THICKNESS!