Fig. 4.1 Thermal con ductivity apparatus

INTRODUCTION 1

Motivation 1

Objectives 2

Possible outcome 2

Scope of the thesis 2

LITERATURE REVIEW 3

Thermal conductivity is considered one of the most important parameters for characterizing the thermal response of leather. Shaving leather has two important objectives, firstly, to even out the substance (thickness) of the leather and secondly, to bring the substance down to an exact number. It is also not possible to establish a relationship between pH and Cr (VI) content in the produced leather.

Sammying and setting is one of the important skin operations and known as double facial tanning process. Softness also varies according to its thickness and the compactness of the fibers in different areas of the same leather. In addition, the thickness of the leather varies according to the surface of the leather through which the gauge pressure acts.

The meter reading i is proportional to the temperature difference of the heaterTH and cooling vessel T. T) T. Thus, the thermal conductivity of the different parts of leather and their comparison can provide important information for its future application.

LEATHER-IT’S CLASSIFICATION AND TECHNOLOGY 4

Definition of leather 4

Classification of leather 4

Processing of leather 5

• Curing 5
• Tanning 6
• Pretanning 8
• Soaking 8
• Fleshing 8
• Unhairing + liming 8
• Deliming and bating 9
• Pickling 9
• Main Tanning and wet-blue 9
• Chrome tanning 9
• Sammying 9
• Sorting 10
• Splitting 10
• Shaving 10
• Wet-finishing and crust 11
• Neutralization 11
• Re-tanning 11
• Drum dyeing 11
• Fatliquoring 12
• Sammying and setting 12
• Drying 12
• Finishing Operation of leather 13
• Conditioning 13
• Stacking 13
• Buffing 14
• Trimming 14
• Finishing and plating 14

The pH of the collagen is brought down to a lower level so that enzymes can act on it, in a process known as decalcification. If the thickness of the leather is not uniform throughout the area, the mechanical effects such as glazing, stacking, ironing, printing, etc. This process is usually performed on wet stock. By comparing the neutralization of wet blue for upholstery crust, clothing and waterproof shoe upper leather carried out conventionally (with sodium formate and sodium bicarbonate) with neutralization when a reducing aid is used, no relationship between the chromate reduction potential of the float and the Cr (VI) content of the learning produced.

Grease rolling is a process in which the surfaces of fibers and fibrils of the leather are covered with a thin layer of oil. A small amount of oil distributed throughout the leather has a significant impact on subsequent finishing operations and the character of the leather. There are various treatments available such as conditioners, impregnating the structure of the leather artifact with active chemicals that are sticky and attract stains.

This should leave some of the grain on the entire skin and results in a cleaner surface. The final conditioning processes are to emboss the skin with heat and pressure to create a selected grain in the skin's surface.

Fig. 3.1 General flow diagram for the leather tanning and finishing processes

Properties of leather (Mechanical or Physical) 15

• Thermal conductivity 15
• Tensile strength and percentage of elongation at break 16
• Tearing strength 16
• Bursting strength 16
• Water vapor permeability 17
• Softness 17

Tensile strength refers to the overall strength of the leather which is determined by small leather customers by pulling the leather with his two hands. Tensile strength is practically determined for all types of light leather such as shoe uppers, linings, upholstery and for industrial leather. Breaking load mainly depends on the number of collagen fibers acting in the direction of applied load and is therefore more or less constant for a piece of leather sample because the number of fibers in that piece is always constant.

The tensile strength of leather in different directions is different because the number of fibers and their texture are different in different directions of leather by nature. This feature is usually applied to the upper part of the shoes as well as to the skins that will be used for leather goods to know the strength of the leather fibers. The tensile strength and the tear strength of the seam thus tell about the strength of the leather, while the tear strength gives an idea of ​​the strength of its fibers.

During tensile strength and puncture tear strength test, large numbers of fibers are ruptured all at once, while in tear strength determination, few fibers are ruptured at once. Bursting strength of leather is measured by the force required to force a spherical plunger through a piece of leather. The burst load and elongation will generally be proportional to the diameter of the plunger.

Water vapor permeability is one of the important properties of leather that makes it so desirable for use in the manufacture of shoes and leather garments due to the sweat that forms inside the shoes and garments. The water vapor permeability of tanned leather is generally high, but is gradually reduced by adding fats, oils and waxes to the tanned leather during finishing. The foot and body can be comfortable under a specific set of temperature and humidity conditions that the wearer of shoes and clothing may encounter.

The rate of penetration of water vapor through the skin is mainly governed by the difference in vapor pressure between the two sides of the skin. It would be desirable to keep the transmission of water vapor at a high level while simultaneously keeping the transmission of liquid water at a low level. The deformability of the skin during measurement will be within the limits of elastic and compact deformations.

EXPERIMENTAL SET-UP AND DATA COLLECTION 18

Design and manufacturing of Fitch type thermal conductivity

Collection of hides and skins 21

The physical properties of leather vary from piece to piece, geographical origin and different locations of the same piece; it is not possible to comment on the average properties of leather just by testing one or two pieces of it.

Preparation of sample 21

Thickness, Softness and Contact area measurement 23

Standard weights used for thickness 370g and softness 530g. Load punch diameter 7mm [softness instrument]. Comparative statement of thickness and softness with respect to sample location and geographical origin in Bangladesh.

Thermal conductivity measurement 37

Here, Q1- heat transfer from the heat source through the sample to the heat sink, Q2- heat stored in the heat sink, t-time, l -sample thickness, k-thermal conductivity of the material, TH-heater temperature , T - heat sink temperature, M- heat sink weight, c- heat sink specific heat, s- heat exchanger surface or heat sink surface. From equation (12) it follows that the graph of log i plotted against t must be a straight line and the slope is m,. The slope m, is determined from the graphs and presented equation (14) to calculate the thermal conductivity.

Experimental Data 40

RESULT AND DISCUSSION 61

• Introductory remarks 61
• Variation of thickness 61
• Variation of softness 62
• Variation of thermal conductivity 64
• Conclusions 66
• Recommendations 67

Of course, the speed of fiber growth, the degree of wave angle, the compactness of the fiber structure and their distribution on the surface vary depending on the origin of the leather. On the other hand, the rotation of the tanning drum, dry grinding and folding can also change the softness of the leather. In this study, softness is measured using a constant-load softness tester at different locations on the leather. The thermal conductivity of porous and water-containing materials largely depends on their porosity and water content.

The fiber compactness, therefore the porosity of the leather is not the same for leather made from a specific cattle or goat. The variation of thermal conductivity of different locations and geographical origins in Bangladesh is shown in Table 5.3 and Fig. Heat transfer through the materials is mainly dependent on its thermal conductivity. Heat can pass faster through material with higher thermal conductivity than lower.

In cold climates, heat loss from inside the shoes will be faster if the thermal conductivity of the shoe material is high. To keep shoes comfortable in cold weather, shoe materials with relatively lower thermal conductivity are generally chosen. These materials protect against heat loss in the shoe in cold weather. Thus, leather from the Dhaka and Chittagong regions is more suitable for use in cold countries. Specifically, the abdomen and the leg, which have a lower thermal conductivity, are better for making shoes than the buttocks and shoulders. In the case of shoes for warm countries, they are porous, i.e. leather with higher conductivity is more suitable. In this investigation, a modified Fitch-type thermal conductivity measuring device suitable for measuring the thermal conductivity of leather samples was designed and manufactured. The thermal conductivity of leather originating from Rajshahi, Dhaka and Chittagong districts of Bangladesh was investigated. The thermal conductivity of the buttock, belly, stem and shoulder of each hide was also investigated.

Variations in softness depending on the geographical origin of the sample and the location of each sample have also been investigated. Variations in the thickness of the butt, belly, shaft and shoulder portion of each leather have also been investigated. The thermal conductivity of leather sourced from Rajshahi district of Bangladesh is found to be 0.149 Watt/mº K and that of leather sourced from Chittagong and Dhaka districts of Bangladesh is 0.102 Watt/mº K and 0.101 Watt/mº K respectively. The highest thermal conductivity occurs in the leather sourced from Rajshahi district, which may be related to its higher value of softness compared to others.

Relatively, lower values ​​of thermal conductivities have been observed in the abdomen and shaft part compared to the buttock and shoulder part. In the present study, the comfort of the shoes can be related to the heat flow inside the shoes and the outside climate, which can finally be related to the thermal conductivity of the leather used to make the shoes. It is observed that leathers from Dhaka and Chittagong regions are more suitable for use in cold countries due to their lower thermal conductivity. More specifically, belly and shaft part with lower thermal conductivity are better for making shoes than butt and shoulder. In the case of shoes. for hot countries like Bangladesh, leather with higher thermal conductivity is more suitable. It was found in this study that leather of Rajshahi origin is more suitable for making more comfortable shoes compared to that of Chittagong and Dhaka origin to Bangladesh and with similar climate to Bangladesh.

Figure 5.1 Variation of thickness at different location and origin of leather

Logogrammatic data of galvanometer defection with respect to origin, location

Calculation of thermal conductivity of leather with respect to sample

Thickness of leather at different location of different region 61