Hair and hide

Fine hair is the biggest seasonal challenge for bovine leather production in the US. The origin, timing and severity of the fine hair problem can be unpredictable and vary from year to year. Seasonal changes in the hair growth cycle are prompted by the lower temperature from autumn to winter; the bovine hair increases in amount, length and thickness. This problem is very old and has increased in severity due to changes in the leather-manufacturing process, cattle breeding conditions and breed diversity. The amount of fat and thickness of the hide also play important roles. The extent of the problem has not been documented and is not fully understood by the scientific community. The presence of fine hair (residual hair) on the wet-blue and final leather is a cause of downgrading the leather. If the wet-blue has fine hair, it cannot be removed in further processing in crust or finishing. Some leather types can tolerate more fine hair than others.

Materials and methods

Wet-blue samples were collected from different suppliers in the US. Crust and finished leathers were supplied from commercial samples from Asian tanneries using US wet-blue. Black Angus hides were brine-cured from Texas and north Texas. Wet-blue, crust and finished leather were analysed by SEM and optical microscope. For optical microscopy evaluations on the grain, cross sections were done using various standard laboratory stereoscopic light microscopes. Electron microscopy evaluation and pictures (SEM) were done with Jeol JSM-6480LV, at 15–20kV. Hair thickness measurements were made by mounting the hairs in five-minute setting epoxy and sanding the epoxy perpendicular to the hairs. The measurements were made on the electron microscope Jeol JSM-6480LV. Other measurements were made directly on the cross sections or on the grain side using the electron microscope.

Cross sections of the salted hides were prepared using a radial microtome with cryostat and stained using Haematoxylin and Eosin as described by Tancous. The Haematoxylin solution Harris modified (HHS16) and Eosin (HT 110116) were purchased from Sigma-Aldrich. Cross sections of the wet-blue, crust and finished leather were prepared using a radial microtome with cryostat and photographed by optical microscope. For the unhairing evaluations we separated the club (average 60μm thickness and 20mm long) and papillary hairs (average 150μm thickness and 60mm long) after removal from salted winter Black Angus hide pieces.

The hairs were mounted on a piece of plexiglass 6×8×8mm. Ten club and 10 papillary hairs were glued with epoxy to the plexiglass. Unhairing solutions were made with sulphide, sulphide plus calcium hydroxide or peroxide in alkaline medium. Sodium dodecyl sulphate was added as a surfactant to reduce the superficial tension. Sodium dodecyl sulphate, sodium sulphide, sodium hydroxide 50%, hydrogen peroxide 35% and calcium hydroxide were purchased from Alfa Aesar. The unhairing tests were run in a 1L glass beaker with 800ml solutions that were placed in a magnetic stirrer with a magnetic bar; the testing was conducted at 23°C for up to 10 hours with very frequent observations. The plexiglass with hairs was mounted parallel to the beaker wall so the hairs were submerged parallel to the liquid surface.

It remains a puzzle why we can have very few fine hairs on a few leathers in a drum. In many cases the hairs are very intact, as if they were immunised and cannot be removed. This happens with winter hairs.

In our opinion what is called ‘fine hairs’ do not refer exclusively to the thin club hairs because both club and papillary hairs are responsible for the ‘fine hair’ problem. The problem could be better defined as ‘short winter hairs’.

Significance to the tanning industry

The US converts about 10 million hides per year to wet-blue, mostly for the export market. Most of the hides are processed fresh, coming straight from the abattoir, still hot and are cooled for proper fleshing before soaking. The hide weight after fleshing ranges 25–50kg. The beamhouse time is less than 24 hours, which includes loading the drum, soaking, unhairing, liming and unloading the drum. The typical drum loads are 16t with 300 to 500 hides per drum. Every year the fine hair problem starts in the autumn – in early to late November. The problem usually peaks from mid-December to mid-January. Most of the time it is completely gone by the end of March. The location of the hair on the wet-blue is usually on the two front pockets and can be extended to the neck area if the problem is aggravated. In severe cases the hair is all over the hide, including the butt area. It is unusual to have hair in the neck (or butt area) without having hair on the front pockets.

Lighter hides and heifers usually have more hair than jumbo hides. The age difference between heifers and animals that have jumbo hides is usually three months. This is probably due to the increased surface area and amount of hair. The heavier hides also have more mechanical action that can dislodge the hair.

Hides from large confinement areas like Amarillo and Finney County have a more uniform size of animal and breed. These areas have an irregular profile for fine hair. Hides from small farms have more diversified size of animal and breeds, and this brings an increased amount of fine hair. There is no pattern to when in the season the fine hair will be visible; sometimes one location may have hair in December, none in January and February, and suddenly the percentage of hair increases in March and April.

During late spring, summer and the beginning of autumn no fine hair is observed. On the drum-bydrum basis it is possible that in one day a few drums will have about 2% of leather with fine hair, and then the next 10 days no hair is observed.

Black Angus is one of the most common breeds in north Texas; in the Texas area, Oklahoma and New Mexico, the zebu and brahma are predominant. These breeds are tropical breeds and will not withstand the harsh winter. Most probably these breeds suffer most with the winter in these locations and therefore produce a heavier and more stable coat in the winter. These hides also have a more intense problem of fine hair.

Salted or brine-cured hides have less problem with fine hair. During salting or brine curing the globular proteins are mostly removed. The hide permeability increases with the addition of salt. These hides require a longer soaking time and are properly soaked for further processing, much better than fresh hides that have a limited and improper soaking.

Our observations do not clearly correlate the reduction of daylight hours to the increase of fine hair. In our opinion the temperature changes, breeds and nutrition play a more important role.

What is surprising is that production can go many days without fine hair, and suddenly the problem appears for a few days and disappears again. Other times only a few drums have five to 10 hides with hair for a period, then the number of hides with hair can increase or simply not exist. Other times the fine hair appears at the end of October or late April, which are times that fine hair should not happen.

US in focus

In cattle raising in the US, we have two important factors that severely affect hair cycling according to the literature: change of hours of sunlight and temperatures. Also, we identified the average winter and summer temperatures for north and south, which show the harsh winter in the north. The daylight hours at summer and winter solstice are also listed; in the north the difference can reach eight hours, and in the south, four hours.

There are several factors that can minimise the fine hair problem:

• Green fleshing: during wintertime the hides accumulate manure that makes it very difficult to properly flesh the hide without damaging it.
• Soaking: there is a need to extend the soaking times to counterbalance the improper fleshing. This is seldom possible because the tanneries run a very tight 24-hour processing time from soaking to liming.
• Drum loads: proper mechanical action is needed during soaking, unhairing, liming and deliming. Overloading in drums does not allow proper mechanical action needed to remove the hair. It is not always possible to reduce the drum loadings.
• Swelling control: when excessive swelling happens, the hair gets trapped inside the hair follicle and no chemical can further attack the hair.
• Uniform loads: there is a proper formulation for different weights of hides that also includes drum weight, alkalinity, reducing agents and auxiliaries. A mixed load can have improper balance and result in an increase on the amount of fine hair. Processing fresh hides makes it almost impossible to weight-break the loads for proper formula use.
• Seasonal formulations: formulations need to be adjusted for winter. Most tanneries have a summer and a winter formula. The formulas need to be used at the correct time.
• Proper formulations: if formulations are not properly balanced for winter, having a security reserve of reducing agents, any variation associated with a process such as process time, improper drainage, float volume, mechanical action, drum load and mixed loads can have improper balance that will increase the amount of fine hair.

The root of the issue

The presence of fine hair on US hides is an old problem and has increased in the past decades due to changes in breed, feed, herd movement and climatic adaptations. The changes in the processing conditions in the tannery have also contributed to this problem. There is limited information on the topic, and the industry has accepted that fine hair is a seasonal problem and cannot be resolved; beamhouse leather producers and customers work to manage it the best way possible to minimise the problem. The resolutions above may go some way to resolving this issue.

This is an abridged extract from the original paper presented  at the IULTCS Congress. The full report with references is available on request.