Advanced Level Dyehouse Course / Module 2

ADVANCED LEVEL DYEHOUSE / MODULE 2

LEARNING OBJECTIVES

Students need to fully grasp the concepts covered on the Intermediate Level Dyehouse Course.

In addition to the Intermediate Level Dyehouse curriculum, the following is covered on this module:

The correct process sequence in the dyehouse

The role of each stage

How each stage is monitored and controlled

The chemicals involved with each stage and possible substitutes

The quality improvement or damage that occurs during the dyehouse processes

Process problems in the dyehouse

Splitting and shaving

Effect of machine processes on the yield of leather from wet blue

Effect of splitting and shaving on the strength of leather

Wetting back

Wetting agents and water tension, surfactant chemistry, enzyme slackening, use use of dicarboxylic acids for binding loose chrome, use of formic acid if rechroming is to be carried out

Rechroming

Rechroming chemicals, properties imparted by chrome tanning materials, dye evenness, batch to batch variation, effect of neutralisation in rechroming float on chrome bound to the collagen, high exhaustion rechroming

Neutralising

Neutralising agents vs neutralising syntans, structure and function of auxiliary syntans, iso-electric point, shifting the iso-electric point, over-neutralisation, complete vs incomplete neutralisation

Protein and leather charge

Retanning

Oxazolidines, melamine, urea-formaldehyde, dicyandiamide resins, replacement, combination, lubricating-acrylic, metal-complex syntans, lignosulphonates, polyurethanes, condensed and hydrolysable vegetable tannins, the binding mechanism of the retanning agents with collagen, properties imparted by the retanning agents, the effect of the retanning agents on the leather, grain effects obtainable with various retanning agents

Acid retanning technology

Problems of loose grain

Leather propreties as a result of the applied syntan

Micro-sphere application

Dyeing

The theory of colour, dyestuff structure, dyestuff selection, dyestuff compatibility, dyeing terminology, factors that affect dye penetration and fixation, dye levelness, dyeing defects, powder vs granular vs liquid dyestuffs, dye effects obtainable with dye technology, dye application methods, colour measurement, trichromatic dyeing, CIELAB colour measurements, dye exhaustion graphs, dyeing auxiliaries

Use of drum pugments to upgrade leather

Metamerism, hue, chroma

Fatliquoring

Emulsion theory, HLB, fatliquor make-up, types of raw oils, synthetic oils,polymer fatliquors, fatliquor manufacture, fatliquor structure, chemical softening and the extended model of fatliquoring, mechanical softening, incomplete fatliquoring, hand / machine oiling and stuffing, hydrophobic fatliquors, pull-up effects, fatliquor defects

Effect of fatliquors on the lightfastness of leather

Effect of fatliquors on the physical properties of leather

Polymer softeners versus conventional fatliquors

Factors determining the fogging of automotive leather

Waterproofing crust leather

Compact dyehouse processes

Classical compact vs ultra-compact processes, advantages and disadvantages

Fixing / washing

Iso-electric point and fixing power, chemical fixing agents, ageing as a fixing mechanism, fixing defects, influence of washing on processing

Charge and fixation

Drying of crust leather, conditioning, staking, milling

The physics of leather drying

Effects of stress / strain during the drying of crust leather

Effect of drying on the characteristics / performance of leather

Technologies to improve the area of leather

Dyehouse processes

Processing upper leather with a tight grain

Processing softy and nappa leathers

Processing of white leather from wet blue

Processing suede and nubuck leathers

Floater leathers

Upholstery leather processing

Prevention of formaldehyde in leather

Reducing veininess in the dyehouse

Prevention of chrome VI during processing

Crust leather testing

Strength, endurance, permeability, shrinkage, dye uptake, chemical uptake, fogging, formaldehyde, hexavalent chromium

Yellowing of crust leather - causes

Ageing of leather

Fatty spews

Emissions from automotive leather

Factors influencing the tear resistance of crust leather