The talk given at ALCA 2015 at Pinehurst Resort. It showcases the ability of the CRC drying method and the use of DMTA analysis to predict drying progression.

1. INVESTIGATING THE CRC MECHANISM USING
DYNAMIC MECHANICAL ANALYSIS.
Flowers, K., Peruzzi, A., Wise, W., and
Covington, A.
2015

2. Part 1 – Drying theory

3. Vaporisation
• Liquid Gas
• Depends on atmospheric
pressure
• Depends on saturation of air
• Inside: boiling
• Surface: evaporation

4. Evaporative factors
• Surface area
• Air capacity
• Relative humidity (dry/wet)
• Speed of air
• Volume
• Heat differential
• Replenishment

6. Replenishment
• Fick’s Second Law
• Tortuosity
• Porosity
High replenishment rate can result
in fibre collapse and cohesion

7. Tortuosity and porosity

8. Sorption/desorption
• When water hydrates the
collagen the fibre heats
• When water is dehydrated it
cools the collagen
Evaporative cooling
• Tannage dependent

9. Physical properties
• Capillary action causes fibres to
undergo cohesion
• Apparent density/ angle of
weave
• Loss of water as a plasticiser
causes the fibre to stiffen
• Stiffness can be measured

10. Dynamic mechanical analysis
• DMTA
• Measures elastic/viscous
property of material
• E’ – storage modulus
• Energy is stored
• E’’ – loss modulus
• Energy is lost as heat

11. Part 2 – Industrial drying

12. Drying Types
• Convection - toggling
• Conduction - vacuum
• Radiation – infra-red
• Hybrids, e.g., paste drying

14. Conditioning
• Very popular in 1950s – 1980s
• Tight grain chromium /
vegetable tanned - vital
• 20 years ago unpopular
• Conditioned milling drums
• Conditioning machines

15. Part 3 – Applied Research

16. Controlled drying
• Jeyapalina proposed a two-
stage drying (2007)
• Drying and conditioning
• Cell rotary conditioning holds
the leather and allows two-stage
• Other drying methods

17. Hypothesis
Can stiffness measured during
drying inform the progress of
drying?
DMTA?

18. Matched Quarters
Cr (only) GTA (only)
Cr (PT) GTA (PT)

19. Methods
• Gravimetric analysis
• To relate % relative humidity to volatiles
• Differential scanning calorimetry
• To understand static thermal properties
• DMTA
• To understand dynamic thermal
properties
• Stiffness change

20. IUC 5
• 98%, 76% and 45% RH
• Retanned chromium leathers
• Domestic upholstery
• Measure the weight change
• Confirmation of other research

22. Figure 1. % Moisture content after pre-conditioning to various % RH at 23°C

23. DSC
• Check the tannage and
shrinkage temperature
• Checked against IUP 16
• Compare tan vs. post tanned

24. Differential scanning calorimetry data obtained from thermal scans of the four types of
leathers used in this study.
Leather type Onset temperature (°C)
Chromium tannage only 104.95
GTA tannage only 75.16
Cr tanned and post tanned 93.89
GTA tanned and post tanned 78.24

25. DMTA
• Dual-cantilever bending mode
• 1 Hz
• 64 μm displacement
• Measure storage modulus over
time (30-40 minutes)
• 85% to 45% declining RH ramp
• 40°C and 60°C

26. Four leather types at 40°C (85 to 45% declining ramp)

27. Four leather types at 60°C (85 to 45% declining ramp)

28. Conclusions
• DMTA can be used to monitor
drying progression
• Can be used to inform optimal
parameters
• Can be used to understand
fundamental properties of
leathers during drying

29. Application
• DMTA can be used in a cell
conditioning system to inform
tension adjustment
• DMTA can be used with links to
physical property data to inform
quality decision-making

30. CRC
• Satisfies University Drying
Research team’s current aims
• Energy-saving (recycled air)
• Tailor-made physical properties
• Tension adjustment
• Chromium-free
• Texture
• Comparable drying times

31. Cell Rotary Conditioning
• Cellular – leather is held in
defined drying conditions
• Convective – drying with strain
or without

32. Cellular
• Independent of outside
conditions
• Independent of operator
competency
• Independent of leather recipe
The machine should compensate

33. Rotary
• Must be cyclised and modular
• Tensioned: variable or static
• Leather changes tension by
itself
• Stress/strain compensation
DMTA can inform the researcher
about predictions