Selected Physical and Mechanical Properties of Alpaca Fibers Differing in Color

ABSTRACT

Demand for alpaca fiber is subject to an increase, which is due to its beneficial properties. The study aimed to determine the differences in physical and mechanical properties, as well as heat insulation properties of alpaca fibers differing in color. The research material consisted of Huacaya alpaca fiber samples of white (W), light fawn (LF), medium fawn (MF), dark fawn (DF), and black (BLK) colors. The following properties were examined: diameter, comfort factor (CF), breaking force, elongation at break, tenacity and heat transfer rate. The finest fibers were found in W and DF fleece, while the coarsest ones in MF. CF was the highest in DF fibers. Breaking force LF varied between 6.4 (DF) and 11.7 cN (BLK), while elongation at break was 43.6 (LF) to 54.7% (BLK). No significant differences were found in case of tenacity. The best insulation properties were found for DF fibers. Correlations were confirmed between diameter and mechanical properties, and they differed slightly depending on colors.

摘要

对羊驼纤维的需求会增加，这是由于其有益的特性. 这项研究旨在确定不同颜色的羊驼纤维在物理和机械性能以及隔热性能方面的差异. 研究材料由白色（W）、浅浅黄色（LF）、中浅黄色（MF）、深浅黄色（DF）和黑色（BLK）的Huacaya羊驼纤维样品组成.测试了以下性能: 直径、舒适系数、断裂力、断裂伸长率、韧性和传热率. W和DF羊毛的纤维最好，MF羊毛的纤维最粗. DF纤维的舒适度最高.断裂力LF在6.4（DF）和11.7cN（BLK）之间变化，而断裂伸长率为43.6%（LF）到54.7%（BLK. 韧性方面没有发现显著差异. DF纤维的绝缘性能最好。直径和机械性能之间的相关性得到了证实，并且它们根据颜色略有不同.

KEYWORDS:

• Heat transfer rate
• fiber
• diameter
• breaking force
• elongation at break
• tenacity

KEYWORDS:

• 纤维
• 直径
• 断裂力
• 断裂伸长率
• 韧性
• 传热率

Introduction

Alpaca (Vicugna pacos) is one of the most important species of domestic animals among camelids living in South America. Breeding of the alpacas is mainly focused on the production of high-quality fibers, highly appreciated in the textile industry due to their properties (Canaza-Cayo, Alomar, and Quispe 2013), and even referred to as “Noble Fibers” (Cruz et al. 2021). Compared to fibers of other animal species, and especially sheep fibers which are the most popular in the textile industry, alpaca fibers are characterized by better mechanical and thermal insulation properties (Cholewińska et al. 2021; Jankowska et al. 2021). Although about 65% alpacas are characterized by white fiber color (Canaza-Cayo et al. 2022; Oria et al. 2009), it is available in up to 22 different natural colors and their shades, from which we can distinguish white, fawn, brown, black, silver gray and rose gray (Cruz et al. 2021; Morante et al. 2009). This makes it a particularly valuable raw material, as it allows to omit the dyeing stage during the processing, which is additionally significant from environmental point of view, thus being a natural alternative with respect to dyed fibers (Atav and Türkmen 2015; Cruz et al. 2021). However, from textile industry point of view, white fibers are valued the most, just due to possibility of their dying into various colors (Atav and Türkmen 2015). Another important feature distinguishing alpaca fibers from other protein fibers is their thickness, which according to various authors mostly do not exceed 30 µm (Machaca Machaca et al. 2017; Quispe Pena, Poma Gutiérrez, and Purroy Unanua 2013; Quispe et al. 2023). Studies were also conducted on the relationship between alpaca fibers diameter and their color, suggesting that white fibers are finer compared to black ones (Lupton, McColl, and Stobart 2006; McGregor and Butler 2004; Morales Villavicencio et al. 2010; Solano and Raggi 2019), although this was not confirmed unequivocally, which prompts to further studies in this direction. In general, the most important features of alpaca fibers from an economic point of view include weight of the fleece, length and diameter of fibers, but also mechanical properties like breaking force, elongation at break or tenacity. Mechanical properties affect fibers processing, but also characteristics of the final product.

The aim of the study was to compare physical, mechanical properties, and heat insulation properties of alpaca fibers differing in color.

Material and methods

The fiber samples were obtained from 2-year-old males of Huacaya alpaca breed, from a farm located in the southern part of Poland. In total, the study included 25 animals with different colors of their fleece: white (W), light fawn (LF), medium fawn (MF), dark fawn (DF) and black (BLK), five animals from each color group. The color of fiber samples was determined based on fiber chart from Alpaca Registry Inc. (https://alpagadore.com/boutique/image/catalog/AA-Atelier/ARI%20COLOR%20CHART_561x800.jpg). Fibers from each animal were collected from the left side of the body at the height of the last rib, in the middle of the regrowth, using a razor.

The diameter of the fibers was measured using a projection microscope MP-3 (lanameter) for 500 fibers from each individual, in accordance with the methodology of textile quality control PN-EN ISO 137: 2016–04. The temperature in the laboratory was maintained at 20°C and humidity was at a level of 40–45%. Based on the results obtained for the fiber diameter, the coefficient of variation (CV) and the comfort factor (CF), as the percentage of fibers with a diameter <30 µm (Frank et al. 2006) were calculated.

The measurements of breaking force and elongation at break were performed in a static tensile test, for 50 fibers from each sample, using a tensile machine from Matest company and computer program “MATEST.” The measurements were made in accordance with PN-EN ISO 5079:1999.

The tenacity was calculated based on the following formula:

$\mathrm{Rm}=\mathrm{Fm}/\mathrm{s}\left[\mathrm{N}/\mathrm{m}{\mathrm{m}}^2\right]$

,

where Fm is the breaking force and s is the cross-sectional area.

The evaluation of heat insulation were carried out on the equipment for the measurement of thermal insulation in materials exposed to thermal radiation produced by Lodz University of Technology (Poland). To evaluate the heat insulation of alpaca fleeces, a 0.3 g sample from each animal was weighed and placed in a holder so that it covered the aluminum calorimeter without squeezing. The sample was placed 40 cm away from the heat source at a temperature of 680°C. The measurement time was 5 min for each sample. For each sample, the factor Rp (°C/s) was determined, expressing the rate of temperature rise of the calorimeter.

Rp = ΔT/Δt

where: Rp – rate of temperature rise of the calorimeter with the sample, °C/s ΔT – temperature rise Δt – heating time.

Subsequently, the factor qs (kW/m²) was calculated – the density of heat flux penetrating the sample.

qs = (m × cp × R)/A × α

where: qs – density of heat flux penetrating the sample (kW/m²), m – the mass of aluminum sample of the calorimeter (0.00716 kg), cp – specific heat of aluminum (900 J/kg °C), A – surface area of the calorimeter (0.00049 m²), α – absorption coefficient of the blackened surface of the calorimeter (0.95).

Measurements were also made for the empty calorimeter to indicate R0 (the rate of temperature rise of the calorimeter without the sample) and q0 (the density of heat flux acting on the sample), to calculate the heat transfer rate (HTR). HTR is a measurement of the heat penetrating through a sample subjected to the thermal radiation. It is equal to the ratio of the density of heat flux that has passed through the sample (qs) to the density of heat flux acting on the sample (q0). The lower the HTR, the better the heat insulation. The measurements carried out on the test bench complied with the requirements of Polish Standard PN-EN ISO 6942:2005.

The study was conducted at the Laboratory of Leather and Hair Cover Evaluation, Institute of Animal Breeding, Wrocław University of Environmental and Life Sciences, Poland.

The results were statistically analyzed using Statistica 13.3 (StatSoft, Poland) and presented as mean values and standard deviations (SD). Normality was verified using Shapiro–Wilk test, while the significance of differences between groups was determined using Kruskal–Wallis test at a significance level of p < .05. To demonstrate relationships between the analyzed features for examined fibers color, Spearman’s correlations were determined at significance level of p < .05.

Results

The finest fibers were found in our study in white and dark fawn alpacas (19.05 µm), while the coarsest were those of medium fawn alpacas (22.91 µm) (Table 1). Dark fawn colored fibers were characterized by the highest CF (98.52%). Significant differences were noted between MF fibers, and DF and BLK (p < .05). On the other hand, the lowest CF was noted for fibers with medium fawn color (91.11%). At the same time, these were the fibers with the lowest (DF) and the highest mean fiber diameter (MF) (Table 1). The CV in all fiber samples tested was below 25%, indicating that they were highly uniform in diameter. The lowest variation was observed in fibers of medium fawn color (Table 1). The results of the mechanical properties, i.e., breaking force, elongation at break and tenacity, are shown in Table 1. DF fibers had the lowest breaking force, while BLK fibers had the highest, and the values were 6.4 and 11.7 cN, respectively. Statistically significant differences were shown between W, LF and MF fibers and DF, as well as between DF and BLK fleece (p < .05). The elongation at break ranged from 43.6% to 55.0%. The lowest value was obtained for LF fibers, while the highest value was obtained for black fibers. Statistically significant differences were confirmed between W and BLC fibers and LF and DF (p < .05) and also between LF and MF (p < .05). The fibers tested were characterized by tenacity in the range of 178.8–203.0 MPa. The lowest value was obtained for DF fibers, while the highest value was obtained for MF fibers. Statistically significant difference was noted between MF and DF fibers (p < .05).

Table 1. Diameter, mechanical properties and HTR of alpaca fibers of different colors.

Property		Color
		W	LF	MF	DF	BLK
Diameter [µm]	X	19.05^a	20.61^b	22.91^c	19.05^a	20.99^b
	SD	4.16	4.65	3.93	3.64	4.46
	V	21.81	22.56	17.17	19.11	21.27
Comfort factor [%]	X	96.67	93.33	91.11^a,c	98.52^b	91.85^c
	SD	2.61	2.81	3.75	0.67	1.99
Breaking force [cN]	X	8.5^a	9.6^a,b	10.1^a,b	6.4^c	11.7^b
	SD	3.0	3.0	2.0	2.0	4.0
Elongation at break [%]	X	53.8^a,c	43.6^d	49.0^b,c	47.6^b,d	54.7^a
	SD	7.53	8.54	6.90	10.35	6.75
Tenacity [MPa]	X	200.7	187.5	203.1^a	178.8^b	190.1
	SD	67.98	56.92	49.23	66.23	38.45
HTR	X	0.64	0.69	0.72	0.50^a	0.74^b
	SD	0.07	0.06	0.07	0.07	0.02

Values in the rows labeled with different letters differ significantly at p < .05.

X – mean value; SD – standard deviation; V – coefficient of variation; W – white, LF – light fawn, MF – medium fawn, DF – dark fawn, BLK – black.

The best insulation properties were found for DF fibers and the poorest ones for BLK ones. Statistically significant differences were noted between DF and BLK fibers (p < .05).

The paper presents correlations between the studied traits without dividing them by coat color and including white, light, medium and dark fawn as well as black coat. The results are presented in Table 2. If coat color is not taken into account, fiber diameter correlates positively with breaking force and elongation at break, but negatively with tenacity (p < .05). There is also a statistically significant positive correlation between breaking force, elongation at break and tenacity.

Table 2. Spearman’s correlations between studied characteristics of alpaca fibers.

	Diameter [µm]	Breaking force [cN]	Elongation at break [%]	Tenacity [MPa]
Regardless of coat color
Diameter [µm]	1.00	0.76	0.33	−0.41
Breaking force [cN]		1.00	0.48	0.23
Elongation at break [%]			1.00	0.17
Tenacity [MPa]				1.00
White coat
Diameter [µm]	1.00	0.78	0.41	−0.45
Breaking force [cN]		1.00	0.63	0.14
Elongation at break [%]			1.00	0.21
Tenacity [MPa]				1.00
Light fawn coat
Diameter [µm]	1.00	0.66	0.23	−0.47
Breaking force [cN]		1.00	0.53	0.28
Elongation at break [%]			1.00	0.27
Tenacity [MPa]				1.00
Medium fawn coat
Diameter [µm]	1.00	0.69	0.26	−0.74
Breaking force [cN]		1.00	0.60	−0.08
Elongation at break [%]			1.00	0.16
Tenacity [MPa]				1.00
Dark fawn coat
Diameter [µm]	1.00	0.51	0.24	−0.59
Breaking force [cN]		1.00	0.44	0.28
Elongation at break [%]			1.00	0.13
Tenacity [MPa]				1.00
Black coat
Diameter [µm]	1.00	0.78	0.42	−0.30
Breaking force [cN]		1.00	0.40	0.32
Elongation at break [%]			1.00	0.02
Tenacity [MPa]				1.00

Correlation marked red significant at p < .05.

Correlations between the fiber characteristics of white coated alpaca fibers demonstrated statistically significant positive correlations between diameter and breaking strength and elongation at break, and a negative correlation between diameter and tenacity (p < .05). In addition, breaking force was found to be positively correlated with elongation at break (p < .05).

A positive correlation between fiber diameter and breaking force and a negative correlation between fiber diameter and tenacity were observed for light fawn fibers (p < .05). Breaking force was positively correlated with elongation at break and tenacity (p < .05).

Considering medium fawn alpaca fibers, positive correlations were noted for diameter with breaking force, breaking force with elongation at break and elongation at break with tenacity (p < .05). A negative correlation was observed between diameter and tenacity (p < .05).

In the case of dark fawn alpaca fibers, a positive correlation was observed between diameter and breaking force, and breaking force and elongation at break and tenacity, while a negative correlation was observed between diameter and tenacity (p < .05).

Taking into account black alpaca fibers, a positive correlation of fiber diameter with breaking force and elongation at break, and a negative correlation between diameter and tenacity were observed (p < .05). Breaking force was also positively correlated with elongation at break and tenacity (p < .05).

Discussion

From an economic point of view, diameter of the individual fibers, except weight, and length, is one of the most important characteristics of the fleece. The diameter of the fiber is also one of commercial traits that are important throughout the whole processing in the textile industry. It case of majority of animal fibers, not only from alpacas, it is a determinant of price, processing performance or final applications (Canaza-Cayo, Alomar, and Quispe 2013).

The results concerning alpaca fiber diameter obtained in our study tend to be lower compared to those obtained by other authors, e.g. 24.3–30.1 µm (Lupton, McColl, and Stobart 2006), 22.16 µm (Montes et al. 2008), 23.68 µm (Solano and Raggi 2019) for alpacas aged 1–3 years. Lupton et al. (2006) found small differences in fiber diameter that could be attributed to color, however in their study the finest fibers were found for light fibers (25.4 µm) and the coarser ones for black fibers (29.5 µm). Solano and Raggi (2019) as well as Morales Villavicencio et al. (2010) and McGregor and Butler (2004) also came to similar conclusions in terms of fiber diameter, however, an inverse relationship was shown in the study of Wuliji et al. (2000). Our study did not show a similar relationship, as the smallest diameter was noted alpacas of both light (white) and dark (dark-fawn) colors.

The diameter of the fibers on the alpaca body is varied. The study conducted by Holt (2007) showed that the finest fibers are located on the back and side of the animal, forming the so-called veil, while the coarsest ones are around the sternum. It has been shown that the animal genotype plays the greatest role in determining the fiber diameter, however, environmental conditions such as climate, nutrition, physiological condition of animals and their coloration are not meaningless (Quispe Pena, Poma Gutiérrez, and Purroy Unanua 2013). Also with age, the diameter of fibers increases (Solano and Raggi 2019), stabilizing around 7.5 years old (McGregor and Butler 2004). Some studies indicate that male fibers are finer than female ones (Radzik-Rant, Pofelska, and Rant 2018), some authors indicate an inverse relationship (Paucar-Chanca et al. 2019), or no differences (Lupton, McColl, and Stobart 2006; McGregor and Butler 2004; Solano and Raggi 2019).

The fiber diameter is also related with the CF. It is a property that indicates the percentage of fibers whose diameter does not exceed 30 µm. Its value should not be lower than 95%. It has been shown that it decreases with the age of the animal. Yarn produced from fibers that exceeds this value can cause the “prickling” effect, which is described by prickling factor – opposite to CF (Frank et al. 2006; Quispe Pena, Poma Gutiérrez, and Purroy Unanua 2013). The study conducted by Solano and Raggi (2019) showed a variation in the CF, depending on the color of the fibers, for white fibers it was 86.1%, brown fibers 90%, mixed fibers 95.5%, while for black fibers it was 76.6%. At the same time, the finest fibers in the study were mixed fibers (21.07 µm) and white fibers (21.71 µm), while the coarsest were black fibers (26.62 µm). In the study by Lupton et al. (2006), lower CF values were obtained for all of the studied coats, ranging from 58.9% for black fibers to 80.8% for white fibers. They also showed that white fibers had the lowest diameter (25 µm), while black fibers were the coarsest (29.5 µm). Thus, in our study, as in the study by Lupton and Solano, it was shown that the larger the fiber diameter, the lower the CF. However, no similar relationship was shown with fibers color.

The variation in the diameter of the fibers in the fleece is measured by the CV. The CV determined for fiber diameter is a measure of the heterogeneity of hair diameter in the fleece. The results concerning CV are similar to those of other studies: 24.33% (McGregor and Butler 2004), 23.6% (McGregor 2006), 25.2% (Wuliji 2017), 19.29–21.61% (Radzik-Rant, Pofelska, and Rant 2018), 23.48% (Lupton, McColl, and Stobart 2006), 19.13% (Paucar-Chanca et al. 2019), 24.3% (Alyan – Parker and Mc Gregor 2002). Only Antonini (2010) obtained a higher result at a level of 36.65%. Lupton et al. (2006) analyzed the variances for fibers of different colors, and showed no effect of diameter or color on its value, similar to our study. It has been shown that this coefficient varies depending on the breed of alpaca. For Suri alpacas it is about 24.4%, and for Huacaya 23.2% (Holt 2007). Also Frank et al. (2006) indicate that for Suri this coefficient is higher. Antonini (2010) indicates that in Suri it is lower (31.85%) than in Huacaya (36.65%). McGregor and Butler (2004) also indicate a relationship between the CV and the color of the fleece. It decreases also with age (Lupton, McColl, and Stobart 2006). A large variety of fiber diameters, so a high CV is treated as a negative feature in the textile industry because it affects the reduction of yarn strength (McGregor and Butler 2004). The results obtained in our study, ranging from 17.17 for MF fibers to 22.56 for LF ones can be considered satisfactory. According to McGregor and Butler (McGregor and Butler 2004), 1 µm change in average hair thickness reflects a change in CV of about 5%, which was not confirmed in our study, as the coarsest fibers were characterized by the lowest CV, which means that the fleece was the most uniform.

The mechanical characteristics of the fibers influencing their processing include, among others, the breaking force, the elongation at break, or the tenacity calculated from the force and diameter. Fibers during processing are exposed to force, therefore high strength properties are important. In a study conducted by Czaplicki (2012), the breaking force value ranged from 0.063 to 0.148N, with the lowest for dark beige fibers and the highest for light beige fibers, and in both cases from Suri alpacas. The lowest value for the Huacaya breed was achieved by the dark brown colored alpaca (0.067N), while the highest value was achieved by the black colored alpaca (0.138N), these were both the samples with the lowest and highest mean fiber diameter. Thus, similar to our research, it was shown that the finer the fibers, the lower the force required to break them.

Czaplicki (2012) obtained similar elongation results, with an average of 45% (ranged from 38% to 51%), while Wuliji et al. (2000) obtained a lower value, with an average of 31.3%. In this study, there was no correlation of elongation at break with fiber diameter or fiber color. In comparison, the elongation at break of sheep’s fibers, which is a breed-dependent value, is, for example, about 34% (German Blackface sheep) or 55% (Romanov sheep) (Ragaišienė, Rusinavičiūtė, and Milašienė 2016), while that of Angora goat fiber is about 40% (Jankowska et al. 2021).

Concerning tenacity, it was shown in a study by Lupton et al. (2006) that darker fibers have lower strength than lighter fibers, which was not confirmed in the study conducted.

HTR results obtained in our study do not allow to conclude unequivocally which fibers, light or dark, are better insulators. Concurrently, the fibers with the best heat insulation properties (lower HTR value) were characterized by the smallest diameter, so it can be assumed that the number of fibers per sample was the highest, which at the same time may affect the increased amount of trapped air between individual fibers and affect the improvement of heat insulation. An additional factor, not investigated in the present study, affecting both the HTR and mechanical properties of the fibers may also be the presence of a medulla in the individual fibers, so it seems reasonable to carry out research in the field of insulation and strength of individual fibers not only with regard to the color of the fiber but also the presence of a medulla. Due to the presence of the medulla in alpaca fibers, they are characterized by better thermal insulation properties compared to sheep fibers (Soroko et al. 2019).

The positive correlations for alpaca fibers of each of the analyzed colors, were generally observed between fiber diameter and breaking force, and between breaking force and elongation at break (p < .05). The strongest correlations were in each case between breaking force and diameter. The only negatively correlated characteristics were fiber diameter with tenacity.

The correlation between breaking force and fiber diameter was also shown by Wuliji et al. (2000). It was a moderate, positive correlation, which ranged from 0.34 to 0.37 (p < .001), depending on the method of diameter measurement. Such a correlation was also shown by McColl et al. (2004). There is not much information in the literature regarding the correlation of the studied traits. However, a positive correlation between diameter and fiber length has been noticed (Paredes-Peralta et al. 2011). It has also been shown that the larger the fiber diameter, the lower the degree of vaulting (McColl, Lupton, and Stobart 2004). A negative correlation (−0.63) between fiber diameter and degree of vaulting is also presented by Wuliji (2017).

McColl et al. (2004) published some of the most extensive findings on the relationship between selected alpaca fiber properties and alpaca coat color. Among others, they demonstrated that fibers from black alpacas are the least vaulted, while light fibers have more crimps. The authors found no statistically significant differences between the strength of dark and light fibers. However, differences were observed in the strength of fibers of different shades of gray.

Lupton et al. (2006) proved the existence of a relationship between coat color and fiber strength. They showed statistically significant differences only in the strength of light-colored fibers and brown fibers. Brown fibers were found to be less strong. This study also compared the compressive strength of alpaca fibers, with white alpaca fibers having the highest values. Fibers from white alpacas had the highest values of this property. Depending on the study, the measurement value was: 5.64 kPa (McColl, Lupton, and Stobart 2004); 5.7 kPa (Lupton, McColl, and Stobart 2006); 5.9 kPa (Wuliji et al. 2000). Fiber from darker animals proved to be less resistant to compression. The lowest measurement value of 5 kPa was obtained for black fibers (Lupton, McColl, and Stobart 2006; McColl, Lupton, and Stobart 2004). According to Wuliji et al. (2000), compressive strength was lowest for dark brown-coated alpacas.

Limitations of our study certainly concern samples size, one location of samples collection or one gender examined, and all these issues deserve further research to recognize factors affecting alpaca fibers features in more detail. Given these limitations, the results obtained in our study apply to the studied population of alpacas rather than to alpacas of different fleece color in general.

Conclusions

The diameter of fibers examined in our study was quite differentiated, but the assumption that light fibers are finer than dark ones has not been confirmed. However, correlations between diameter and mechanical properties have been found to be significant. A more thorough understanding of the mechanical properties of the fibers, the correlations between them, and the factors influencing the value of the traits can be useful information both for breeders and textile industry.

Highlights

• Physical and mechanical properties of hair differ depending on color.

• Correlations were confirmed between diameter and mechanical properties.

• Dark fawn fibers were characterized by the best insulation properties.

Disclosure statement

No potential conflict of interest was reported by the author(s).