INVESTIGATING THE CRC MECHANISM USING DYNAMIC MECHANICAL

ANALYSIS.

Flowers, K., Peruzzi, A., Wise, W., and Covington, A.

2015

Part 1 – Drying theory

Vaporisation

• Liquid Gas• Depends on atmospheric

pressure• Depends on saturation of air

• Inside: boiling• Surface: evaporation

Evaporative factors

• Surface area• Air capacity

• Relative humidity (dry/wet)• Speed of air• Volume

• Heat differential• Replenishment

Replenishment

• Fick’s Second Law• Tortuosity• Porosity

High replenishment rate can result in fibre collapse and cohesion

Tortuosity and porosity

Sorption/desorption

• When water hydrates the collagen the fibre heats

• When water is dehydrated it cools the collagen

Evaporative cooling• Tannage dependent

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

Dynamic mechanical analysis

• DMTA• Measures elastic/viscous

property of material• E’ – storage modulus

• Energy is stored

• E’’ – loss modulus • Energy is lost as heat

Part 2 – Industrial drying

Drying Types

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

Conditioning

• Very popular in 1950s – 1980s• Tight grain chromium /

vegetable tanned - vital• 20 years ago unpopular• Conditioned milling drums• Conditioning machines

Part 3 – Applied Research

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

Hypothesis

Can stiffness measured during drying inform the progress of

drying?

DMTA?

Matched Quarters

Cr (only) GTA (only)

Cr (PT) GTA (PT)

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

IUC 5

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

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

DSC

• Check the tannage and shrinkage temperature

• Checked against IUP 16• Compare tan vs. post tanned

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

 

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

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

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

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

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

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

Cell Rotary Conditioning

• Cellular – leather is held in defined drying conditions

• Convective – drying with strain or without

Cellular• Independent of outside

conditions• Independent of operator

competency• Independent of leather recipe

The machine should compensate

Rotary

• Must be cyclised and modular• Tensioned: variable or static

• Leather changes tension by itself

• Stress/strain compensationDMTA can inform the researcher about predictions

Thank-you