ISSN 2953-6367  
http://revistainvestigo.com  
Julio - diciembre 2026  
Vol. 7 No. 20, PP. 1027-1044  
https://doi.org/10.56519/7jg6rm60  
ANÁLISIS CRÍTICO DE MÉTODOS SOSTENIBLES ALTERNATIVOS  
PARA EL BLANQUEAMIENTO DE LA FIBRA DE ALPACA: UNA  
REVISIÓN BIBLIOGRÁFICA  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS  
FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
Sebastián Guerrero-Luzuriaga1, Araceli Agualongo2, Anthony Janeta-Ordoñez3, Byron  
Herrera-Chávez4, Cristian Patiño-Vidal5  
{saguerrero@unach.edu.ec1, janeth.agualongo@unach.edu.ec2, anthony.janeta@unach.edu.ec3, bherrera@unach.edu.ec4,  
cristian.patino@unach.edu.ec5}  
Fecha de recepción: 16/06/2026  
/ Fecha de aceptación: 07/07/2026  
/ Fecha de publicación: 08/07/2026  
RESUMEN: La fibra de alpaca es un recurso muy valioso para la industria textil gracias a su  
suavidad, durabilidad y capacidad térmica. Aunque el blanqueamiento resulta una etapa  
esencial durante su procesamiento, también genera importantes desafíos económicos y  
ambientales. Esto se debe al alto consumo de agua y energía, además del uso frecuente de  
agentes químicos agresivos. Por ello, este trabajo analiza distintas alternativas sostenibles  
frente a los métodos convencionales, con el objetivo de minimizar el impacto ecológico sin  
comprometer la calidad del material. Entre las opciones evaluadas se encuentran el peróxido  
de hidrógeno, el uso de extractos vegetales y los tratamientos enzimáticos, junto con  
tecnologías emergentes como el ultrasonido. La implementación de estas innovaciones permite  
reducir la dependencia de sustancias tóxicas como el cloro; al mismo tiempo, optimiza el uso  
de los recursos y disminuye la generación de residuos. A través de la revisión bibliográfica se  
contrastan las ventajas y limitaciones de cada técnica, evaluando parámetros como la eficacia  
del blanqueado, la conservación de las propiedades físico-mecánicas, la sostenibilidad y la  
viabilidad tanto técnica como económica. Gracias a este enfoque integral, es posible identificar  
soluciones prácticas que combinen calidad, fomentando un procesamiento mucho más  
responsable de la fibra de alpaca.  
1Faculty of Engineering, Safety and Resources Valorization Research Group (INVAGRO), Faculty of Engineering, Universidad  
Nacional de Chimborazo (UNACH), https://orcid.org/0000-0001-9512-2307  
2Independent Researcher, https://orcid.org/0009-0007-9541-284X  
3Independent Researcher, https://orcid.org/0000-0002-2132-3111  
4Faculty of Engineering, Safety and Resources Valorization Research Group (INVAGRO), Faculty of Engineering, Universidad  
Nacional de Chimborazo (UNACH), https://orcid.org/0000-0003-1116-9939  
5Faculty of Engineering, Safety and Resources Valorization Research Group (INVAGRO, Faculty of Engineering, Universidad  
Nacional de Chimborazo (UNACH), https://orcid.org/0000-0002-5633-6908  
1027  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
Palabras clave: Fibra de alpaca, Blanqueamiento, Sostenibilidad, Industria textil, Tecnologías  
emergentes  
ABSTRACT: Alpaca fiber is a highly valuable resource for the textile industry due to its  
softness, durability, and thermal properties. Although bleaching is an essential step in its  
processing, it also poses significant economic and environmental challenges. This is due to high  
water and energy consumption, as well as the frequent use of harsh chemicals. Therefore, this  
study analyzes various sustainable alternatives to conventional methods, with the goal of  
minimizing the ecological impact without compromising the quality of the material. Among the  
options evaluated are hydrogen peroxide, the use of plant extracts, and enzymatic treatments,  
along with emerging technologies such as ultrasound. Implementing these innovations reduces  
dependence on toxic substances such as chlorine; at the same time, it optimizes resource use  
and reduces waste generation. Through a literature review, the advantages and limitations of  
each technique are compared, evaluating parameters such as bleaching efficacy, the  
preservation of physical-mechanical properties, sustainability, and both technical and  
economic feasibility. Thanks to this comprehensive approach, it is possible to identify practical  
solutions that combine quality with a much more responsible processing of alpaca fiber.  
Keywords: Alpaca fiber, bleaching, sustainability, textile industry,emerging technologies  
INTRODUCTION  
Alpaca fiber holds a recognized position in international textile markets for its thermal efficiency  
and tactile profile, but agroindustrial processing runs into a hard constraint at the bleaching stage.  
Conventional treatment has depended almost entirely on hydrogen peroxide. The oxidant  
produces high whiteness index values consistently, but the tradeoffs are significant. Water and  
energy consumption is disproportionate, but the real issue is structural. Oxidative action breaks  
the disulfide bonds in alpha-keratin; as a result, it erodes the cuticle's topography and  
permanently reduces both breaking strength and fiber elasticity.  
Between 2019 and 2024, research shifted toward three cleaner alternatives. On one hand,  
ultrasound-assisted acoustic cavitation cuts processing time by nearly two-thirds by improving  
chemical penetration. However, the mechanical energy involved often generates microcracks  
that ultimately weaken the elastic modulus. On the other hand, enzymatic treatments using  
cellulases and pectinases, along with botanical extracts (particularly white nettle infusions and  
decoctions), exhibit a different behavior. Both improve colorimetric results and lower the  
yellowness index without the oxidative load that damages cuticle morphology. By avoiding  
aggressive oxidants, they successfully preserve the surface's scaly structure and mechanical  
resistance—elements that hydrogen peroxide systematically compromises.  
While these findings are promising, they remain scattered across the literature. Until now, there  
is no unified framework assessing the actual tradeoff between bleaching efficiency and physical  
preservation of the material; furthermore, its industrial scalability remains uncertain. For this  
reason, the present study critically examines sustainable bleaching alternatives for alpaca fiber  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
compared to conventional chemical treatments. Specifically, the objectives focus on comparing  
the colorimetric performance of each method, evaluating the physical-mechanical changes in the  
processed fiber, and analyzing its surface morphological alterations using scanning electron  
microscopy. The underlying hypothesis is that enzymatic biotechnology and botanical extracts  
can reach competitive textile standards while preserving fiber structural integrity and reducing  
the ecological footprint of the bleaching process at scale.  
METHODOLOGY  
Data collection techniques and instruments  
Data were collected through a review of articles from scientific databases including Google  
Scholar, ScienceDirect, Taylor & Francis, SciELO, and Fibers and Polymers, using keywords in both  
Spanish and English: "fiber bleaching," "alpaca fiber," "ultrasound," "enzymes," "hydrogen  
peroxide," "plant extracts," "white nettle," "physical properties," "mechanical properties,"  
"colorimetry," and "scanning electron microscopy." To gather relevant literature, the search  
strategy relied on specific phrases, including "enzymatic treatments for textile fiber bleaching,"  
"application of ultrasound in natural fibers," and "bleaching of wool and alpaca with hydrogen  
peroxide." The query also incorporated terms like "use of plant extracts in textile processes,"  
"white nettle as a natural bleaching agent," and "modification of the cuticular surface in alpaca  
fibers," alongside searches focused on "color analysis in bleached fibers" and "evaluation of  
physico-mechanical properties in treated fibers." Once collected, the information was classified  
and selected based on key criteria: the effectiveness of the bleaching method, structural changes  
observed in fiber morphology, color variations measured via colorimetry, and the overall impact  
on mechanical resistance.  
Study population and sample size  
To evaluate the effect of alternative sustainable methods on alpaca wool bleaching, secondary  
information was collected from 150 documents including scientific articles, research papers, and  
theses. After applying inclusion and exclusion criteria, 95 records were discarded. Of the  
remaining 57 relevant articles selected by title and abstract, 23 were eliminated, leaving 75  
articles. After applying exclusion filters and reading the full content, 22 articles were included in  
the study. For the physico-mechanical properties of wool after bleaching treatment, secondary  
information was gathered from 52 documents including scientific articles and theses. After  
applying inclusion and exclusion criteria, 20 records were discarded. Of the 27 relevant articles  
selected by title and 31 by abstract, 9 were eliminated, leaving 18 articles, of which 6 were  
included in the final analysis.  
Analysis Methods  
Following PRISMA guidelines, the collected information was analyzed using scientific articles and  
theses related to natural fiber bleaching methods, with a focus on alpaca fiber. Results from  
studies using ultrasound, enzymes, hydrogen peroxide, and plant extracts were considered in  
1029  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
order to compare their effectiveness and conduct a critical analysis of the morphological,  
colorimetric, and mechanical changes induced in the fiber. The PRISMA methodology, applied  
through a four-phase flowchart — identification, screening, eligibility, and inclusion —  
determined the specific number of documents used in the literature review. This process ensured  
a structured and transparent analysis of the information, following predefined inclusion and  
exclusion criteria.  
Data processing  
The collected information was organized and managed using the Mendeley platform, classifying  
documents into sections related to alternative fiber bleaching methods, variations in yellowness  
and whiteness indices, physico-mechanical properties, and morphological changes observed in  
the cuticular surface. The selected articles were organized chronologically from newest to oldest.  
For efficient bibliographic management, each entry was integrated directly into Word and  
included an abstract summary, a link to the document, and its corresponding APA 7th edition  
citation. To clearly present the findings, the results for methodologies like ultrasound, enzymes,  
hydrogen peroxide, and plant extracts were divided into specific sections. Each section detailed  
the sequential impact of the treatment on the fiber. Finally, key data—such as yellowness and  
whiteness indices, mechanical resistance, and morphological changes—were compiled into  
comparative tables. Structuring the information this way facilitated a critical and substantive  
discussion regarding the true effectiveness of these alternative methods.  
PRISMA Method  
This study used the PRISMA methodology to ensure a systematic and transparent process in the  
selection of scientific literature. Through a four-phase flowchart — identification, screening,  
eligibility, and inclusion — the specific number of articles and documents used in the literature  
review was determined. This procedure made it possible to organize the information in a  
structured and reliable manner, facilitating critical analysis of the different alternative methods  
applied to alpaca fiber bleaching, including ultrasound, enzymes, hydrogen peroxide, and white  
nettle plant extracts.  
PRISMA Inclusion Criteria  
The following articles were considered for the review:  
•
•
Articles addressing alternative bleaching methods for natural fibers, particularly wool or  
alpaca fiber.  
Articles presenting results related to yellowness and whiteness indices, physico-mechanical  
properties, or fiber morphology modifications.  
•
•
Articles published within the past six years.  
Articles written in English or Spanish.  
PRISMA Exclusion Criteria  
1030  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
The following articles were excluded from the study:  
•
Articles that do not provide information on alternative bleaching methods for natural fibers  
or lack results applicable to alpaca fiber.  
•
•
•
Articles published more than six years ago.  
Articles that do not meet the minimum criteria after title and abstract review.  
Articles duplicated across the consulted databases.  
Figure 1. Prism diagram for the critical analysis of alternative sustainable methods for bleaching alpaca fiber.  
RESULTS  
A comprehensive literature search was conducted using Google Scholar, SciELO, ScienceDirect,  
Web of Science, and PubMed. The search employed the keywords "bleaching," "alpaca fiber,"  
1031  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
"yellowness index," "whiteness index," "morphology," "physico-mechanical properties,"  
"ultrasound," "enzymes," and "plant extracts" to identify relevant studies published between  
2019 and 2024. A total of 150 publications, including peer-reviewed articles and graduate theses,  
were initially retrieved. Following a rigorous screening and critical evaluation process, 22 studies  
addressing sustainable alternative bleaching methods and 6 studies focused on the physico-  
mechanical properties of alpaca fiber were selected for detailed analysis.  
The findings are organized into three comparative tables that summarize the reported effects of  
the evaluated bleaching treatments on key quality parameters, including the Yellowness Index  
(YI), Whiteness Index (WI), physico-mechanical properties, and scanning electron microscopy  
(SEM) morphology. These parameters provide a comprehensive assessment of the effectiveness  
of the alternative bleaching methods and their influence on the structural and functional  
characteristics of alpaca fiber.  
1032  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
Yellowness and Whiteness Index  
Table 1. Studies related to yellowness and whiteness index.  
No.  
Author  
(Cruz et  
Topic  
Year  
Language  
Database  
Journal  
Sciences Direct  
Colorimetric analysis of fleece color and its relationship to fiber  
characteristics in alpacas.  
English  
Google  
Scholar  
1
2021  
al.,2021)  
Phenotypic and genetic relationships between fiber and color  
traits in South American camelids.  
English  
English  
English  
Google  
Scholar  
2
3
4
(Frank, et  
al.2019)  
2019  
2019  
2025  
Sciences Direct  
Sciences Direct  
Genetic parameters of medullary fiber and their relationship  
with productive traits in alpacas.  
Google  
Scholar  
(Cruz A et al.,  
2019)  
Colorimetric and textile properties of Huacaya alpaca fibers dyed  
with cochineal: a sustainable approach.  
Google  
Scholar  
Journal of Social and  
Environmental  
Management  
(Quispe et al.,  
2025)  
Comparison of fiber quality characteristics and fiber length in  
Suri and Huacaya alpacas.  
English  
English  
Google  
Scholar  
Frontiers in Animal  
Science  
5
6
(Pinares et al.,  
2023)  
2023  
2025  
Color phenotypes, genotypes, and colorimetry of unprocessed  
North American Huacaya alpaca fiber with comparisons to other  
common natural fibers.  
Google  
Scholar  
(Baxter et al.,  
2025)  
Sciences Direct  
Assessment of natural color variation and its impact on fiber  
quality parameters in high-altitude Huacaya alpacas.  
English  
English  
Spanish  
Google  
Scholar  
7
8
9
(Rodriguez et  
al., 2024)  
2024  
2022  
2020  
Textiles Research  
Journal  
Spectrophotometric evaluation of whiteness and yellowness  
indices in alpaca fleece: implications for textile processing.  
Web of  
Science  
(Thompson et  
al., 2022.)  
Journal of Natural  
Fibers  
Relationship between colorimetric parameters (Lab*) and textile  
quality in white and colored alpaca fibers.  
SciELO  
(Gonzales et  
al., 2020. )  
Peruvian Journal of  
Veterinary Research  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
Physico-Mechanical Properties  
Table 2. Studies related to the physico-mechanical properties of alpaca fiber.  
No.  
Author  
Topic  
Year  
Language  
Database  
Journal  
Selected physical and mechanical properties of alpaca  
fibers with different colors.  
English  
ScienceDirect  
Journal of Natural Fibers  
1
(Czyż et  
al.,2024)  
2024  
Characterization and evaluation of mechanical  
properties of blended yarns based on alpaca and milk  
protein fibers.  
English  
Google Scholar Journal of Social and  
Environmental  
2
(Mamani et al.,  
2024)  
2024  
Management  
Characteristics of Huacaya alpaca fiber in Peru:  
mechanical properties and diameter analysis.  
English  
English  
ResearchGate  
Small Ruminant Research  
3
4
(Ali et al., 2021)  
2021  
2023  
Tensile strength and elastic modulus in alpaca fibers: a  
comparative study between Huacaya and Suri  
varieties.  
Google Scholar Textile Research Journal  
(Silva et  
al.,2023)  
Mechanical behavior of alpaca fiber under different  
environmental conditions.  
English  
Spanish  
English  
Scopus  
SciELO  
Scientific Journal  
5
6
7
(Thompson et  
al., 2022. )  
(Bustinza et al.,  
2019)  
(Czyż et al,  
2024)  
2022  
Physical and mechanical properties of fine alpaca fiber:  
influence of age and fleece position.  
Revista de Investigaciones  
Veterinarias del Perú  
2019  
2024  
Selected physical and mechanical properties of alpaca  
fibers with different colors. Journal of Natural Fibers,  
21(1), 2348626.  
Google Scholar Taylor & Francis  
Comparative analysis of tensile properties across  
different grades of alpaca fiber.  
Spanish  
English  
Google Scholar Scientific Journal  
8
9
(Chen et  
al.,2020)  
(Bouagga et al.,  
2018)  
2020  
2018  
Correlation between mechanical behavior and  
chemical, physical, and thermal characteristics of wool:  
a study on Tunisian wool.  
Taylor &  
Francis  
Journal of Natural Fibers  
Comparison of physico-mechanical properties of fiber  
and yarn made from alpaca, sheep, and goat wool.  
English  
Taylor &  
Francis  
Journal of Natural Fibers  
10  
(Jankowska et  
al., 2019)  
2019  
1034  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
SEM Morpholohy  
Tabla 3. Studies related to fiber morphology by SEM.  
No.  
Author  
Topic  
Year  
Language  
Database  
Journal  
Physical characteristics and fiber diameter profile of Huacaya  
alpacas from the La Raya experimental center (Puno, Peru), by age  
and sex.  
2021  
Spanish  
Google  
Scholar  
Revista peruana de  
biotecnología  
1
(Quispe et el.,  
2021)  
Influence of ultraviolet radiation and protease on the scale  
structure of alpaca wool fibers.  
2020  
2018  
English  
Spanish  
Google  
Scholar  
AUTEX Research  
Journal  
2
3
(Wang et al.,  
2020)  
Morphological and elemental analysis of alpaca hair by scanning  
electron microscopy with energy dispersive X-ray spectroscopy  
(SEM-EDX).  
Google  
Scholar  
Thesis  
(Mucha et al.,  
2018)  
Application of artificial intelligence and digital image analysis to  
automatically determine the medullation percentage of fibers in  
alpaca fleece samples.  
2022  
2023  
English  
English  
Google  
Scholar  
ScienceDirect  
4
5
(Bonilla et al.,  
2022)  
Analytical methods for identification and quantitative  
determination of wool and fine animal fibers.  
Google  
Scholar  
Journal of Natural  
Fibers  
(Marina et al.,  
2023)  
An efficient ultrasound-assisted bleaching strategy for yak hair  
activated by a Fenton reaction targeting melanin.  
2022  
English  
Google  
Scholar  
ScienceDirect  
6
(Li q et al.,  
2022)  
An eco-friendly bleaching method for cashmere fiber with  
hydrogen peroxide and maleic acid in scCO2 avoiding heavy  
effluent discharge.  
2024  
2013  
English  
English  
Google  
Scholar  
ScienceDirect  
7
8
(Fan Wang Et  
Al., 2024.)  
Accurate identification of cashmere and wool fibers based on  
improved ShuffleNetV2 and transfer learning.  
Google  
Scholar  
Journal of Big Data  
(Zhu Et Al,  
2023)  
1035  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
Analysis of Results: Yellowness and Whiteness Index  
Table 4. Whiteness Index (WI) and Yellowness Index (YI).  
WI  
Before  
Bath  
YI  
Before  
Bath  
Bleaching  
Conditions  
(Temp. / Time)  
YI  
After  
Bath  
Bleaching  
Method  
WI After  
Bath  
Reference  
26.41  
30.48  
60°C / 30 min  
5.43  
74.3  
11.91  
72.83  
86–87  
57.65  
(Guerrero &  
Janeta, 2024)  
(Lozano et  
al., 2023)  
(Guerrero &  
Hydrogen  
Peroxide  
5.19  
83.1  
90°C / 60–90 min  
26.41  
30.48  
Decoction  
Plant Extract  
(White Nettle)  
extracts 60°C /  
30 min  
Janeta, 2024)  
26.41  
40–50  
150  
30.48  
25–30  
75–85  
45  
Infusion extracts  
60°C / 30 min  
40–60°C / 2–6  
hours  
11.99  
56.87  
22.57  
38.33  
40  
(Guerrero &  
Janeta, 2024)  
(Salamanca  
et al., 2019)  
(Orcón,  
2019)  
(Serrano et  
al., 2023)  
15–  
25%  
0.5  
Enzymatic  
Bleaching  
50–98°C  
0.37  
35–50°C / 15–30  
min (500W,  
35kHz)  
60  
Ultrasound  
Bleaching  
92  
32  
60, 70 and 80°C  
80  
95  
(Ollancaya et  
al., 2023)  
Several alternative bleaching methods are used in the textile industry, the most relevant being  
hydrogen peroxide, sodium bicarbonate, plant extracts, enzymatic bleaching, and ultrasound  
bleaching. These treatments served as benchmarks for comparing the effects each has on the  
fiber during the bleaching process.  
Hydrogen peroxide treatment applied at a controlled temperature of 90°C for 60 to 90 minutes  
improved fiber color characteristics. The results showed a 10.6% drop in the yellowness index  
according to the ASTM D1925 standard, falling from an initial 83.1 to 74.3 and improving the  
overall tone (1). Simultaneously, the whiteness index climbed to values between 86 and 87,  
reflecting a substantial upgrade in color purity. These specific conditions help optimize the entire  
process. At a high temperature of 90°C, hydrogen peroxide becomes highly active as an oxidizing  
agent; this allows it to diffuse much faster through the alpaca fiber and effectively break down  
the naturally occurring melanin pigments (2).  
Leaving the fiber exposed for 60 to 90 minutes ensures the bleaching agent penetrates evenly  
throughout the fibrillar structure. This timeframe achieves a consistent decolorization without  
significantly compromising the material's mechanical properties (3). Chemically speaking,  
hydrogen peroxide generates perhydroxyl ions (HO₂⁻) during the bath. These ions transfer oxygen  
and specifically attack the disulfide bonds present in the wool. By breaking down these S-S  
linkages, the hydrogen peroxidation process makes complete whitening possible (4).The  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
bleaching action of hydrogen peroxide works by eliminating fat and the yellow tint caused by the  
decomposition and solubilization of pigmented granules (5,6).  
Samples bleached exclusively with natural extracts showed lower yellowness and whiteness index  
values compared to those treated with hydrogen peroxide and other methods. This is because no  
partial or total removal of pigments and impurities (fat and sebum) occurred, given the minimal  
presence of oxidizing agents responsible for removing such impurities5. Despite this, natural  
extracts still managed to bleach the wool effectively relative to raw fiber, improving the white  
color by 52% and reducing yellowness by 45%. This bleaching effect can be attributed to the  
action of the active compounds in the extracts on the sheep wool (7).  
Enzymatic bleaching of alpaca fibers using cellulases and pectinases under controlled conditions  
(40–60°C for 2 to 6 hours) produced measurable improvements in colorimetric parameters.  
Treated fibers showed initial whiteness index values between 40 and 50, and yellowness index  
values of 25 to 30. After treatment, the yellowness index dropped to the 15–25 range and the  
whiteness index improved to 65–70% (8). In alternative protocols using higher enzyme  
concentrations and elevated temperatures (50–98°C), initial whiteness index values of 150 and  
yellowness index values of 75–85 were reported. After treatment, the yellowness index dropped  
sharply to 0.5, while the whiteness index improved to 38.33 (9). The bio-polishing process using  
cellulases affects not only colorimetric parameters but also tensile resistance and fabric weight,  
reflecting structural changes in the fiber. Enzymes represent a viable alternative to toxic chemical  
agents, contributing to more sustainable processes. The effectiveness of enzymatic bleaching is  
attributed to cellulases, which can selectively hydrolyze surface cellulose, removing impurities  
and improving fiber accessibility without significantly compromising structural integrity (10).  
Ultrasound bleaching applied to alpaca fibers under controlled conditions (35–50°C, 15–30  
minutes, 500W at 35kHz) produced clear colorimetric improvements. Starting whiteness index  
values of 0.37 and yellowness index values of 45 improved to whiteness index values of 60 and  
yellowness index values of 30, along with increased fiber clarity (11). At higher temperatures (60,  
70, and 80°C), additional gains were recorded, with whiteness index values reaching 92 and  
yellowness index reductions to 32, reaching final optimized values of 80 and 95 respectively (12).  
Ultrasound bleaching with hydrogen peroxide takes approximately one-third of the time required  
by conventional hot methods, nearly doubling the initial whiteness index of the fibers. This  
efficiency is attributed to acoustic cavitation, which facilitates uniform penetration of bleaching  
agents, ensures even distribution of the treatment, and significantly reduces processing time (13).  
1037  
CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
Analysis of Results: Physic-Mechanical Properties  
Table 5. Physic-mechanical properties of ovine fiber.  
Bleaching  
Method  
Diameter  
(μm)  
Breaking  
Force  
Maximum  
Deformation  
Elastic Modulus  
327.39 ±36.79  
67.89 ±11.86  
70  
Reference  
Untreated  
Wool  
27.93± 0.43  
14.68± 0.43  
25.54  
47.59 ±1.26  
5.88 ±0.87  
60-110  
37.24 ±2.32  
16.99 ±2.73  
15-20  
(Guerrero  
et al., 2024)  
(Guerrero  
et al., 2024)  
(Lozano et  
al., 2023)  
(Guerrero  
et al., 2024)  
(Guerrero  
et al., 2024)  
(Kozłowski  
et al., 2020)  
(Vaca et al.,  
2021)  
Hydrogen  
Peroxide  
Plant Extract  
(White  
Nettle)  
20.21 ± 0.60  
20.42 ± 0.57  
18.5 ± 2.1  
22.1 ± 1.9  
10 – 14  
30.28 ±0.89  
29.42 ±0.94  
12.3 ± 1.8  
10.8 ± 2.1  
600 - 800  
13.6 ± 1.9  
39.29 ±1.14  
39.44 ±1.02  
8.7 ± 1.2  
167.58 ±19.74  
152.77 ±15.03  
2.8 ± 0.4  
Enzymatic  
Bleaching  
7.4 ± 0.9  
3.2 ± 0.5  
1.8 – 2.0  
10.0 – 16.0  
3.1 ± 0.4  
(Li Q et al.,  
2020)  
(Hosseini et  
al., 2023)  
Ultrasound  
Bleaching  
19.3 ± 2.0  
8.9 ± 1.1  
Hydrogen peroxide treatment at a concentration of 25.54%, applied for 60 to 110 minutes at  
temperatures of 15 to 20°C, significantly affects the structural properties of alpaca fiber. The  
formation of hydroxyl radicals (·OH) and reactive oxygen species attacks the disulfide bonds in α-  
keratin specifically. As these oxidizing agents transfer oxygen, they progressively break the S-S  
covalent bonds. This reaction reduces the fiber's breaking force to roughly 70 units, marking a  
substantial drop compared to untreated fibers (14). Disulfide bonds actually play a fundamental  
role in maintaining keratin’s structural integrity. Within alpaca fiber, the alpha-keratin forms  
helical structures that rely on these intermolecular bridges for stability, creating a highly resistant  
three-dimensional matrix (13). Consequently, when oxidation ruptures these bridges, the  
material's mechanical resistance is directly compromised. Though the oxidative treatment breaks  
a significant number of disulfide bonds, it introduces compensatory hydrogen bonds that help  
maintain fiber elasticity under dry conditions at values comparable to untreated fiber. In short,  
higher hydrogen peroxide concentrations and longer exposure times translate directly into lower  
breaking force in alpaca fibers. Keratose obtained by oxidative extraction with peracetic acid or  
hydrogen peroxide is hygroscopic, water-soluble, and susceptible to hydrolytic degradation at  
extreme pH values, confirming that hydrogen peroxide-bleached fibers show compromised  
physico-mechanical properties compared to other bleaching methods (10).  
When applied to alpaca fibers, enzymatic bleaching acts primarily on keratin, the core structural  
protein of the material. Unlike conventional chemicals, enzymes catalyze highly specific reactions  
to selectively degrade the chromophore groups responsible for color. Because of this targeted  
approach, they manage to lighten the material without completely altering the conformation of  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
the alpha-keratin helices. As a result, this mechanism largely preserves the integrity of the  
disulfide (S–S) bonds, which are essential for maintaining the fiber's overall mechanical resistance  
(15). Cellulases and pectinases hydrolyze glycosidic bonds and secondary peptides present in the  
outer layers of the fiber, facilitating the removal of associated impurities and pigments without  
drastically compromising the internal network of covalent bonds. Enzymatic bleaching is  
therefore a less aggressive alternative than traditional chemical methods, maintaining to a  
greater degree the chemical and mechanical structure of protein fibers like alpaca while still  
achieving the desired decolorization effect (16).  
Ultrasound bleaching in alpaca fibers modifies keratin primarily through cavitation. During this  
process, microbubbles form and collapse in the liquid medium, releasing intense energy that  
produces microcurrents and shock waves. These physical effects not only improve the  
penetration of bleaching agents but also generate free radicals capable of breaking bonds in the  
keratin structure (17). As a result, the fiber loses part of its mechanical resistance: breaking force  
drops from normal values of 19.3 ± 2.0 cN/tex to 10–14 cN/tex, the elastic modulus decreases  
from 13.6 ± 1.9 to 600–800 cN/tex, and maximum deformation shifts from 8.9 ± 1.1% to just 1.8–  
2.0%. In other words, while cavitation makes the treatment faster and more effective, it can also  
cause significant structural damage to keratin, negatively affecting the physico-mechanical  
properties of alpaca fiber (18)  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
Figure 2. Analysis of SEM images of fibers bleached using different methods, as reported in scientific articles.  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
DISCUSSION  
In its natural, unprocessed state (Illustration 2a), wool presents an intact cuticular surface made  
up of overlapping scales. At 1000x magnification, the characteristic rough texture of the fiber  
cuticle is clearly visible, along with circular structures distributed across the surface associated  
with fat and sebum residues typical of unprocessed wool. These features reflect the presence of  
lipid compounds and natural contaminants covering the fiber, which must be removed through  
subsequent cleaning and bleaching processes to optimize both the optical properties and  
mechanical behavior of the wool (4).  
With conventional hydrogen peroxide bleaching (Illustration 2b), at 1000x magnification, the  
cuticular surface is heterogeneous, with areas where the scales appear eroded or detached. This  
morphological pattern reflects the oxidative effect of hydrogen peroxide on keratin, the fiber’s  
structural protein, causing alterations in its surface organization. Detached circular structures are  
also visible, indicating partial degradation of the lipid and protein components associated with  
the cuticle, which confirms the combined oxidation and solubilization induced by the treatment.  
Under 1000x magnification, the surface of fibers treated with non-conventional ultrasound  
Bleaching (Illustration 2c), displays slight wear. At the cuticular level, the cavitation generated by  
the ultrasound partially fragments the scales and triggers the formation of microcracks. As a  
result, the fiber takes on a more eroded and heterogeneous appearance compared to untreated  
samples. This process also causes localized detachment of the cuticular material, exposing more  
of the internal matrix and pointing to a weakening of the surface keratin. Ultimately, these  
structural shifts highlight a key tradeoff: while ultrasound effectively improves chemical  
penetration during the bleaching process, it simultaneously alters the external architecture and  
compromises the morphological integrity of the material (19).  
Illustration 2d and 2e show plant extract bleaching at 1000x magnification. These fibers present  
a relatively smooth surface with well-defined scales, suggesting that natural agents can be  
effective for bleaching without compromising the structural integrity of the fibers. This is due to  
the presence of active compounds and the minimal amount of oxidizing agents they contain (20).  
Illustration 2f and 2g show enzymatic bleaching at 1000x magnification. The cuticular cells,  
responsible for keeping the fiber firm and compact, undergo progressive wear. Enzymatic action  
breaks down surface components and affects the integrity of the cuticle, leading to a loss of  
structural cohesion in the fiber. This is visible in the SEM image as increased roughness and  
detachment of cuticular scales, similar to the wear observed with other chemical methods such  
as hydrogen peroxide. These microscopic changes indicate the impact of bleaching on the  
mechanical resistance and durability of the fiber (15).  
Industrial scalability is a critical factor when assessing the viability of textile bleaching methods  
for protein fibers like alpaca wool. Conventional hydrogen peroxide bleaching is already firmly  
established in the textile industry, with standardized processes available at large scale. Its main  
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drawback is the degradation of the fiber’s mechanical properties and the heavy demand for water  
and energy associated with pH and temperature control, which produces a considerably high  
carbon footprint (21).  
Enzymatic processes, in contrast, have shown in pilot studies on cotton and linen the potential to  
significantly cut chemical and energy consumption, making them compatible with more  
sustainable industrial approaches (10,22). At large scale, however, their implementation faces  
constraints around enzyme stability under industrial conditions and the cost of enzyme  
production, factors that still limit their competitiveness relative to traditional chemical agents.  
Ultrasound presents itself as a complementary technology that can improve the action of  
chemical or enzymatic agents by reducing processing times and operating temperatures. Pilot-  
scale reactor studies have demonstrated whiteness improvements and reduced peroxide use,  
suggesting a positive effect on carbon footprint through lower chemical and energy loads (23).  
Moving to large-scale production, however, presents significant challenges. Facilities must  
overcome the high energy demands and maintenance costs associated with ultrasound  
equipment, factors that currently limit its widespread commercial use.  
Plant extracts, on the other hand, offer an emerging alternative that relies on biodegradable  
natural compounds to lower direct environmental impacts. While specific data on alpaca fiber  
remains scarce, previous experience with cellulosic fibers points to a smaller carbon footprint  
simply by cutting back on synthetic chemicals. Scalability faces challenges related to standardizing  
the concentration of active metabolites and securing plant biomass in industrial volumes, factors  
that could compromise the sustainability of large-scale use.  
CONCLUSIONS  
Analysis of the main bleaching methods for alpaca fiber shows that hydrogen peroxide remains  
the most effective and industrially established agent, given its low cost and broad availability. Its  
effectiveness depends, however, on strict control of variables like time and temperature. When  
these are not optimized, the protein structure of keratin is compromised, negatively affecting  
physico-mechanical properties such as resistance and elasticity.  
Plant extracts, particularly from white nettle, offer a promising alternative aligned with  
sustainability trends. Unlike peroxide, these treatments reduce structural damage to the fiber,  
preserving its morphology and improving its physical performance. Bleaching efficiency does  
depend on critical parameters including the standardization of extracts, temperature control, and  
treatment duration, which pose real challenges for industrial adoption.  
The incorporation of non-conventional technologies such as ultrasound represents a meaningful  
advance. The cavitation phenomenon allows more uniform distribution of bleaching agents,  
cutting process time and reducing the severity of operating conditions. The method combines  
technical efficiency with lower chemical consumption, though large-scale implementation still  
faces barriers around energy use and the adaptation of specialized equipment.  
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CRITICAL ANALYSIS OF ALTERNATIVE SUSTAINABLE METHODS FOR BLEACHING ALPACA FIBER: A LITERATURE REVIEW  
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