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Summary of full report
November 2003
RIRDC Publication No 03/128 RIRDC Project No UD-2A
Introduction
Alpaca fibre is soft, luxurious
and has a range of natural colours and good strength. Australia has great
potential for a viable alpaca industry with sound pastures and modern technologies
for breeding the best genotypes. For the development of Australian alpaca
fibre industry, there has been a strong demand for research into fibre
properties and processing, as well as product development along the value-adding
chain. This is the first major research project, funded by RIRDC, to assist
the Australian alpaca industry and fibre processors, to develop better
understanding of the fibres and their processing performance.
The key project components and findings are summarised in the following sections.
Alpaca Fibre Properties
and the Benefit of Improved Classing Practice
Australian alpaca fibre
was traditionally classed into broad micron and length ranges due to the
small quantity of fibres available. A range of properties of the alpaca
fibres, grouped according to colour, length, and fineness were examined
objectively to demonstrate the benefit of improved classing practice. The
results in this study have shown that the traditional broad classing leads
to large variations in fibre properties such as fibre diameter and staple
length within the classing lines. The Australia alpaca fibre industry has
started to adopt a new classing practice with tighter micron ranges and
more clearly defined length groups during the course of this research program.
Australian white alpacas have less medullated fibres than overseas alpacas. The staple strength of Australian alpaca fibres is significantly higher than that of wool staples and the strength of single alpaca fibres is also marginally higher than that of wool fibres of similar diameter. The within fibre diameter variation in alpaca fibres is lower than that in wool fibres.
Alpaca Fibre Scouring
Scouring is one of the key
issues for the alpaca industry. Several alpaca scouring trials have been
conducted to identify an efficient alpaca fibre scouring method. Results
of solvent extractions, ash contents and fibre yield indicate that there
is no significant difference between the scouring regimes in terms of scouring
performance. All scouring methods examined can achieve satisfactory removal
of grease. However, no methods can achieve an ash content below 1%. The
high ash content may affect the processing performance of alpaca fibres.
Dedusting greasy alpaca fibres can remove about 2% dust, reduce the dust
level around the scouring machine and improve scouring efficiency slightly.
Scanning Electron Microscope (SEM) study revealed that fine dust particles may be bound with the fibre surface, making them difficult to remove. Alpaca fibre has a higher scouring yield (around 90%) than greasy wool.
Conventional wool scouring regime or the wool scouring regime with a low level of detergent application can be used for alpaca fibre scouring.
Processing Performance
of Alpaca Fibres
Three trials have been conducted
to examine the performance of alpaca fibre processing. For all trials,
the production rates of carding and combing alpaca fibres were well below
the wool production rate.
This was necessary to minimise fibre damage and reduce processing problems.
Both carded and combed alpaca slivers lack fibre cohesion. This creates problems for the sliver transfer and delivery. Two approaches have been attempted, strengthening the sliver cohesion by adding twists and shortening the distance the sliver has to travel. Single alpaca rovings also lack strength. The rovings should be coarser than 600 tex to prevent roving breakage during spinning.
Blending alpaca fibre with wool adds the value of wool fibre and enhances the processibility of alpaca
fibre. The wool component is beneficial to the strength of the blend due to the much higher crimp of wool in the blend.
The mean fibre diameter (MFD) increases by about 0.5-1µm as the processing of alpaca fibre proceeds from carding to top stages. The combing noils are 1-3µm finer than the alpaca tops. This makes tops coarser than the pre-combing slivers.
A high ash content on the scoured fibre and high moisture content for reducing the static problem can cause significant residual build-up on the gilling machine front rollers. As such, problems were encountered with sliver periodically jamming in the coiler during each gilling passage. Achieving low ash content is a major task for alpaca fibre scouring.
Static build-up results in frequent machine stoppages and a high mass variations in slivers, rovings and yarns. Maintaining the correct processing conditions is also very important for the quality of alpaca slivers and yarns. The relative humidity in the processing mill should be maintained at a level higher than 80% to minimise the static problems.
Quality Comparison of
Alpaca Yarns from Different Sources
The quality of alpaca tops
and yarns was assessed. Test samples were commercial products manufactured
overseas and by local fibre processors, plus experimental samples. The
test results could assist with the benchmarking of product quality for
Australian alpaca fibre industry.
The fibre diameter in an alpaca/wool blend is usually coarser than the wool fibre diameter. In an overseas alpaca/wool blend, the MFD of wool fibre is up to 3µm finer than the alpaca fibre. Australian alpaca fibre processors use wool fibre 7µm finer than the alpaca fibre in an alpaca/wool blend. A sliver linear density of approximately 25 ktex is commonly used for alpaca tops. Fine alpaca fibre can produce more even tops than coarse alpaca fibre.
The twist factor of single alpaca yarns affects the yarn strength and fabric handle. As the twist factor increases, yarn strength increases (up to a limit), but fabric handle gets worse. Low twist yarns break easily during spinning and knitting. In addition, when using yarns with the same twist factor, knitted alpaca fabrics shed more fibres than wool fabrics. An overseas yarn manufacturer used a twist factor of around 100 (Metric) for single yarns. However, local fibre processors use a twist factor less than 90 for all singles yarns. For all folded yarns, the twist factor is less than 70. The selection of alpaca yarn twist factor should therefore depend on the application of the yarns. Unlike knitting wool yarns that have a twist factor of less than 80, it is suggested that knitting alpaca yarns have a minimum twist factor of 80, in order to maintain an acceptable strength for knitting.
Alpaca Yarns with Improved
Softness
Spinning results indicated
that low twist factor yarns, which are softer than high twist factor yarns,
could be engineered. However, reducing yarn twist level increases ends-down
during spinning. Results of alpaca fabric handle subjective assessment
showed that reduced twist factor did improve fabric softness, but low twist
yarns broke easily during knitting. It is therefore expected that fibre
processors would experience difficulties for low twist factor yarns and
knitters would prefer relatively high twist yarns.
Sirofil was employed to produce low twist factor yarns using alpaca/wool blends twisted with a nylon filament in a single operation during yarn spinning. The Sirofil yarns of alpaca/wool/nylon are stronger and have larger extensibility and rupture energy than their corresponding normal ring spun yarns. More importantly, the Sirofil yarns have a low initial modulus, and hence the yarns are softer than normal ring spun yarns.
Blending alpaca fibre with high-crimp superfine wool fibre can enhance fibre processibility of a blend and the comfort of yarns.
Understanding of the Softness
Attributes of Alpaca Fibres
To achieve objective measurement
of alpaca fibre softness, the usefulness of testing method (Resistance
to Compression) for wool was evaluated. This study has demonstrated the
profound difference between wool and alpaca fibres in their resistance
to compression (RtC) behaviour, which is surprising, considering both are
animal fibres. The RtC value of scoured alpaca fibre (in the range of 25-30µm)
is about 5kpa on average, which is much smaller than that of most fine
and super fine wool fibres (17-20µm). The resistance to compression
is highly co-related with the curvature of wool fibres, but this co-relation
is not as apparent for alpaca fibres. In comparison to wool, alpaca fibres
have much lower curvature and scale protrusion, which reduce the bulk of
the fibre mass and its frictional resistance under compression, both leading
to reduced resistance to compression. This study suggests that the results
from the current resistance to compression test method are not suitable
for lowcurvature alpaca fibres, and it is not a good softness indicator
for fibres of varying diameters. Many factors should be considered together
for softness assessment, such as fibre surface properties and mechanical
properties.
A new testing method for evaluating fibre softness was introduced and a testing rig for the softness measurement of fibre bundles was developed in this study. The new softness testing method can achieve good discrimination between fibres of varying levels of softness, such as alpaca and wool, based on the measured specific forces of pulling a fibre bundle through a series of pins. The specific pulling force reflects the combined effect of fibre surface properties, fibre diameter and fibre rigidity.
Fibres with finer microns, lower bending modulus and smoother surface have a lower specific pulling force and are softer, and the effect of fibre crimp or curvature on the specific pulling force or fibre softness is small. Preliminary results also showed that alpaca fibre could have the same softness as wool fibre that is up to 12µm finer. Further research is warranted in this area.
Alpaca Fabrics Softness
and Pilling
The softness of fabrics
is affected by many factors such as yarns and fabric structures. Fabrics
were knitted using yarns of different twist factors and types and their
handle was assessed subjectively. For the yarns with the same twist level,
alpaca fabrics are softer than wool fabrics, even when the mean fibre diameter
of alpaca fibre is coarser than that of wool. Fabrics knitted with low
twist alpaca yarns or yarns engineered with finer alpaca fibres have softer
handle than high twist or coarser fibre yarns.
Alpaca fabrics are softer than alpaca/wool blends of the similar specifications.
Knitted alpaca fabrics have less propensity to pill, but their surface is fuzzier than wool fabric. Pilling performance of alpaca fabrics improves when the yarn twist is increased.
Bleaching of Pigmented
Alpaca Fibres and Dyeing of Bleached Fibres
Progress has been made in
bleaching of coloured alpaca fibres and dyeing of the bleached fibres.
Two bleaching methods for dark coloured alpaca fibres are evaluated in
this report. The bleach method-I (BL-I) uses half the concentration of
H2O2 used in bleaching method-II (BL-II). A trial has been conducted to
bleach dark brown (DKBR) alpaca tops/yarns and dye the bleached product.
Both bleached and dyed tops were then engineered into yarns. Bleached dark
alpaca fibres provide a good base for dyeing the fibres into a more attractive
medium or deep shades. These shades will enhance the value of dark coloured
alpaca. The bleaching method-I leads to a good finished top that retains
the strength of the untreated brown alpaca fibres. This method causes less
fibre damage and should be used where retaining the properties of the alpaca
fibre is important. Fibre bleached with method-I has a reduced lightness
and better chromaticity than that with method-II. Fibre bleached with bleaching
method-II exhausts less dye than BL-I. The wash fastness of the finished
products from BL-II is on average 1 grey scale unit poorer than BL-I, and
the dyed top does not maintain the depth or clarity of the colour after
laundering.
Bleaching and dyeing of the alpaca fibre causes a reduction in yarn tenacity and elongation. When colour reduction in pigmented fibres becomes more important than fibre damage, moderate losses in strength can be offset by the advantages offered by bleaching.
Bleaching method-II leads to about 2.3µm reduction in mean fibre diameter. This increases the number of fibres in the cross section of the BL-II yarns of a given count. This results in an improvement in yarn evenness and strength. But yarn hairiness also increases. The increased fibre damage recorded for BL-II may have contributed to the higher level of hairiness of the bleached and bleached/top dyed yarns.
Fibre surface modification and scale removal due to bleaching affect the speed of fibre moisture absorption. Bleached alpaca fibre is quicker to absorb water from the air in the first few hours after it is removed from drying.
It is recommended from this study that a lower concentration of hydrogen peroxide (such as that used in BL-I) can be used to minimize fibre damage but still achieve a light colour base for dyeing pigmented alpaca fibre. The process of top bleaching then yarn dyeing is recommended to reduce yarn strength and evenness problems associated with the top bleached/top dyed fibre.
Fibre Curvature and Alpaca/Wool
Blend
Fibre curvature has become
an important fibre attribute to the fibre processing performance and its
end-product quality. This report studied the fibre curvature of wool and
alpaca fibres and their changes during the early stage of fibre processing.
The performance of alpaca/wool blend yarns and fabrics has also been investigated.
The curvature of scoured alpaca fibre is normally much less than half the
curvature of scoured wool fibre. Like wool fibre, the curvature of alpaca
fibre decreases as the mean fibre diameter increases.
During early stages of alpaca fibre processing, alpaca fibre has less curvature reduction compared to wool. Curvature reduction in alpaca tops is about half as much as that in wool fibre. Fibre/pin interactions or edge crimping may generate excessive curvature, such as during carding. Alpaca top relaxation in warm water could remove the generated curvature, particularly in tops manufactured from medium and strong alpaca lines.
Alpaca fibre has low crimp and its surface is smooth. This makes the alpaca fibre difficult to process, particularly during fibre/sliver transfer. Blending alpaca fibre with wool improves the cohesion of the blend sliver, especially when alpaca is blended with high-crimp wools. For a high ratio of alpaca component in the blend, high-crimp wool should be used to improve sliver cohesion.
Fibre curvature in the alpaca/wool blend is smaller than that in wool component. After relaxing the blend tops in warm water, the curvature in the blend is still smaller than the relaxed wool.
There is no significant difference in yarn count and yarn evenness between alpaca/low-crimp-wool blend and alpaca/high-crimp-wool blend yarns when they were processed the same way.
Surprisingly, the knitted fabric made from alpaca/high-crimp-wool blend is softer than that made from alpaca/low-crimp-wool blend. This may be explained by the test results that the initial modulus of alpaca/high-crimp-wool blend yarn is lower than that of alpaca/low-crimp-wool blend yarns.
It is recommended that the selection of wool fibre curvature for alpaca/wool blend should depend on the blend ratio and end-uses. Generally, wool fibre crimp is not critical to the quality of the blends.
However, for alpaca and superfine wool blends, high-crimp-wool may be preferred if the ratio of alpaca fibre component is high and low-crimp-wool may be preferred if the ratio of alpaca component is low in the blend.
Calculating MFD and CVD
of Alpaca/Wool Blend
A model for computing the
MFD and CVD in a mixture of multiple fibre components has been developed.
Validation results show that this model can accurately calculate the MFD
and CVD of a blend from the parameters of the individual components. The
developed model has a wide range of applications, including determining
the minimum yarn count or number of fibres in a blend yarn crosssection,
and choosing the right blend ratio and fibre properties for a blend. Examples
of alpaca/wool blends are given to demonstrate such applications. A table
is created for alpaca/wool blend, which provides good reference data for
the alpaca processors.
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