Keratin hydrolysate as a chrome exhaust aid and keratin filler in

Overview

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Key numbers

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replace the commercial protein filler (Celatan F: 50, 75, and 100 %) with KH solution, with
concurrent processing of control leather using conventional chrome tanning agent at 6 % dosage
mechanical strength, organoleptic properties and thermal stability were obtained with 100 %
substitution of Celatan F at pH 6 and 10 % chromium dosage. It was also discovered that the
(aldehydes, vegetable tannins, and resins) (8) to fill the interfibrillar void space created due to the removal of unwanted protein
limited exhaustion rate that does not surpass 50–70 %, making chromium the major constituent of tannery effluent (11). Discharge
hydrolysis (19). The extracted keratin has been used for a wide range of applications, such as for fertilizer industries (27); for
oratory chemicals and reagents used for analysis are of analytical grade and includes sodium hydroxide (NaOH), 99.0 %; hydrochloric
acid (HCl), 37 % w/w; sulfuric acid (H2SO4), 98 %; nitric acid (HNO3), 65 %; perchloric acid, 70 %; sodium chloride (NaCl), 99.5 %;
boric acid, 99.5 %; and basic chrome sulfate (33 % basicity). All the laboratory chemicals and reagents including process chemicals for
solution was subsequently adjusted to the necessary pH of 4.2 using a 2 M HCl (37 %) solution. The precipitated KH solution was then
centrifuged at 10,000 rpm for 5 min to produce keratin powder. Table 1 shows the experimental variables considered and protein yield
%Ash = × 100 (1)
minimum values of COD (mg O2/L), TDS (g/L), and % Cr2O3 (g/L). The stainless-steel pilot reactor employed for the extraction
3.2 before the application of keratin hydrolysate according to the methods in Tables 2 and 3. The tanning process was applied to both
the experimental and control samples, using 6 % basic chromium sulfate (33 % basicity). The percentage of the chromium’s primary
same proportion (20 %) of pH-adjusted KH extract solutions was applied one at a time. The temperature, drum revolution per minute in
ranges of 20–35 ◦ C, 6–8, 40–100 %, and 6 %, respectively. The seventy-five pieces of fresh sheep skin purchased from the Addis Ababa
Run No. Actual factors Absorbance at 540 nm Protein concentration (mg/mL) % protein yield
Based on the weight of fleshed pelt, a constant KH dose of 20 % in solution or 1.43 % in powder form based on the KH solution solid
matter of 0.0721 g/mL was utilized. For both the experimental and control processes, the same amount of chromium was used (6 %
which should be closer to the dose of commercially available chemicals for chrome exhaustion (1.5 % of MgO) (48). Therefore, 30
solution and 2.5 %, 2.2 %, 1.8 %, 1.08 %, 0.7 %, and 0.4 % in powder form, respectively based on the solid matter (0.0721 g/mL) of the
%Cr2 O3 = (2)
process based on the designed methods, as shown in Table 4A number of retanning processes were conducted at different pH values of
5, 6, 7, and 8, substituting the commercial protein filler (Celatan F) with the produced keratin filler (50 %, 75 % and 100 %). This
ammonium was then treated with an alkaline solution (50 % sodium hydroxide) to convert it to ammonia, and the mixture was distilled
extraction time (3.5 h), and protein yield (88.6 %) were attained. The treated samples were taken in triplicate to determine the ash
content, and the results are depicted in Table 5. As the table shows, the average ash content from the analysis data was 12.73 % of the
sample weight, which is in consistent with the value reported by Ref. (27), slightly higher than the one reported by Ref. (18), 10 % and
falls in the range of 30–40 % w/w” (18). This indicates that the experimental extract has relatively less hazardous inorganic oxides and
stretching motions of the amide functional group and absorbed water account for the relatively broad peak in the range of 3250–3300
The effects of five pH values of KH solution (4.5, 5, 6, 7, and 8), the percentage of the applied KH solution (5 %, 10 %, 15 %, 20 %,
25 %, 30 %, and 35 %), and the points of application (before or after tanning) were considered in the optimization study. Several runs
with KH solution at different pH values ranging from 4.5 to 8 and percentage dosages ranging from 5 % (0.4 % in powder form based on
when the KH solution was applied at pH (5) than at pH (4.5) as depicted in Table 6, which is due to precipitation of KH at pH (4.5) that
value of pH 5 and pH 6, as shown in Table 6. On the other hand, it was demonstrated in Table 9 that chromic oxide in the spent liquor
Trial No. 1 2 3 Mean ± SD
Effects of varying pH and points of application on the %Cr2O3 content of wet blue leather.
pH Dosage of KH solution (%) Points of application % Cr2O3 in the wet blue leather (Mean ±SD)
(6). Furthermore, there was an improvement in the leather mechanical strength and organoleptic properties. Table 6 demonstrate that
TDS and Cr2O3 analysis results for tanning spent liquors at a 20 % KH dosage.

Methods (brief)

provided 6 kg of sheep hair waste for extraction purpose. The composite method of sampling was used to obtain samples of sheep hair
Science and Technology University (ASTU) and Addis Ababa Science and Technology University (AASTU).
paint unhairing, the raw sheep hair sample was washed many times with enough warm water. The sample of washed sheep hair was
bicarbonate (1 g/L), ammonia (1 g/L), and an anionic degreasing agent (1 g/L). The treated hair sample was subsequently cut into
carry out the experiment. 20 g of the samples were soaked in 0.25 L of 0.4 N, 0.70 N, or 1 N NaOH solutions for 1.5, 2.5, or 3.5 h, at 65,
80, and 95 ◦ C, respectively. The samples and solution of the hydrolyzing agent were placed in conical flasks, which were subsequently
prepare for dialysis, the KH solution was concentrated once more in a water bath. The samples were then subjected to membrane
The total ash content of the keratin powder sample was determined according to the Society of Leather Technologists and Chemists,
SLC6 (IUC 7; BS 1309:6) (46,47). 5 g of the KH sample were weighed and placed in a pre-weighed, clean, and dry crucible dish. It was
preheated to 750 ◦ C and heated at that temperature for 3 h. The total ash content of the hair samples was calculated using Equation (1).
weight of hair sample
for the pilot-scale extraction; however, the amount and concentration of the solution, including the sample of sheep hair, were scaled
process, the raw sheep hair used, the extracted product KH at pilot scale and sample 25 mL kH solution were as shown in Fig. 1a,b, 1c
the experimental and control samples, using 6 % basic chromium sulfate (33 % basicity). The percentage of the chromium’s primary
spent liquors from both the control and experimental operations were collected.
After aging for at least 48 h, wet blue samples were taken from both the experimental and control process drums for the shrinkage
Finally, chrome liquors from the control and experimental processes drums were collected for chromic oxide, COD, and TDS analysis.
sheepskin samples were employed for these experiments, considering various concentrations of 35, 30, 25, 15, 10, and 5 % KH in

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised