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Original article
Influence of knitted fabric constructionon the ultraviolet protection factor of greige and bleached cotton fabrics
Wai-yin Wong1, Jimmy Kwok-Cheong Lam1, Chi-wai Kan1 and
Ron Postle2
Abstract
The alarming increase of incidence of skin cancer has hastened development of ultraviolet (UV) protective clothing andresearch on UV protection of apparel. Although various fabric parameters that affect ultraviolet radiation (UVR) trans-mission were studied by researches, most of them focused on woven fabrics and chemical approach in enhancing UV
protection. There were few studies concerning knitted fabrics, in particular the influence of fabric constructions onultraviolet protection factor (UPF) and structural properties. The magnitude of transmission and scattering of UVRthrough a fabric is decided by fabric construction or knit structure, which is classified by geometrical arrangement of yarns and fibers of the fabric. This paper aimed at studying the influence of different knit structures upon the UPF withthe three main knit stitches incorporated in the knitted fabric constructions, namely the knit, tuck and miss stitches. TheUPF and structural characteristics, including thickness, weight, stitch density and porosity of greige and bleached knittedfabrics with different knit structures, are compared by adopting factorial analysis of variance. The results show thatfabrics with miss stitches possess a higher UPF than fabrics with tuck stitches. The double-knitted fabrics have better UVprotection than the single-knitted fabrics overall, but bleaching has different impacts on the UPF of single- and double-knitted fabrics. The study reveals that fabric thickness or weight cannot be used solely in explaining the UV protectiveperformance of knitted fabrics. However, fabric porosity can be a good indicator for UV protection when comparingfabrics with similar fabric weight and thickness but different structures or fiber contents.
Keywords
Ultraviolet protection factor, knit structures, weight, thickness, stitch density, porosity
Evidences were found globally that there is an increas-
ing number of people dying from skin cancer each year
and it is apparent that over-exposure to ultraviolet radi-
ation (UVR) is deemed to be one of the main reasons.1
Skin cancers are very common in the UK, with more
than 70,000 new cases diagnosed each year.2 In the US,
skin cancer is the most common cancer, which accounts
for nearly half of all cancer types with more than
2 million cases found each year.3 Skin cancer is also
the most common cancer type in Canada, which
accounts for an estimated one-third of all new cases
of cancer and its incidence rate continues to rise.4
Australia has the highest incidences of skin cancer in
the world which is almost four times the rates in the
UK, the US and Canada. Skin cancers account for 80%
of all newly diagnosed cancers in Australia and two in
three Australians will be diagnosed with skin cancer by
the time when they are 70.5 In Hong Kong, non-mela-
noma skin cancer is the eighth most common type of
cancer diagnosed, with over 717 new cases each year.6
The deleterious impacts caused by over-exposure to
UVR have increased the public awareness of the need
to adopt personal UV protective strategies, such as the
1Institute of Textiles and Clothing, The Hong Kong Polytechnic
University, Hong Kong2School of Chemistry, University of New South Wales, Australia
Corresponding author:
Jimmy Kwok-Cheong Lam, Institute of Textiles and Clothing, The
Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Email: [email protected]
Textile Research Journal
83(7) 683–699
! The Author(s) 2013
Reprints and permissions:
sagepub.co.uk/journalsPermissions.nav
DOI: 10.1177/0040517512467078
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use of sunscreens on the parts of body that are exposed
to the sun. However, the protection provided by sun-
screens is not long lasting and requires frequent supple-
ment after a period of time due to continuous sweating
from the skin. Inappropriate usage of sunscreens, such
as applying an insufficient amount or thickness on the
skin, may attenuate the original UV protective ability.Although clothing, which acts as the ‘second skin’ of
human can provide some protection against harmful
UVR and the market value of UV protective clothing
is noteworthy, clothing can only provide limited protec-
tion against UVR, in particular for knitwear with a more
porous and stretchable structure than the woven gar-
ments. Many textile manufacturers try to enhance the
UV protective performance of garments using a chem-
ical approach with the use of dyes, whitening agents and
UV absorbers such as titanium dioxide or zinc oxide.
Nevertheless, the photodegradation of fabric dyes, opti-
cal brightening agents and the potential hazard of these
chemicals to the human body lacks investigation. The
study of Khazova et al.7 indicated that there is a degrad-
ation of efficiency of the optical brightening agents, as
well as photochemical degradation of fabric dyes after
prolonged exposure to UVR. It reveals the problems
about the sustainable function provided by UV protect-
ive finishing on textile products, including pollution and
excessive water consumption brought by chemical treat-
ments giving rise to environmental concerns. Many
researchers have studied various fabric parameters that
influence UVR transmission, such as fiber compos-
ition,8–11 fabric construction,11–16 yarn twist,17,18 thick-
ness,8,10,19
weight,19
wetness or moisture content,20–22
stretch or extensibility,20,22,23 chemical treatment or
additives and coloration.24–32
However, most of the studies have concentrated on
the above fabric parameters with woven fabrics only,
whereas there have been few studies concerning knitted
fabrics, in particular the influence of knitted fabric con-
struction on UV protection. Stankovic et al.17 and
Wilson and Parisi20 have studied UV protection prop-
erties with knitted fabrics, but neither of them expli-
cated how the knit structures exactly influence UV
protection of fabrics., Stankovic et al.17 studied the
ultraviolet protection factor (UPF) of grey-state plain
cotton knitted fabrics by investigating the impact of
yarn twist and surface geometry instead of the knitted
fabric constructions. Wilson and Parisi20 compared the
UV protection provided by two knit structures (eyelet
and pique) and two weave structures; however, the fab-
rics were composed of different fiber contents. The UV
protective ability of fabric depends on the amount of
UVR reflected or absorbed by fibrous materials, trans-
mitted through pores between fiber and yarn, and also
scattered within the fabric layer. Fabric construction is
one of the important factors affecting these paths for
UVR. The arrangement of yarns and fibers determined
by fabric construction can influence the compactness of
the structure, together with the open space within the
fabric. Other physical properties, such as the amount of
open area produced when tension is applied or the
amount of shrinkage after laundering, are presumably
in connection with fabric construction.Moreover, many researchers agree that dyes can
increase the UVR blocking property of a fabric and
darker colors can provide better UV protection. The
use of UV absorbers even gives excellent UV blocking
performance to fabric. Nonetheless, knitted fabrics have
more complex fabric geometry, rather a porous structure
and are more elastic than woven fabrics. It should be
noted that the UV protection of fabrics enhanced by
chemical treatment is only sufficient when the fabric
structure is compact enough.14 Knitted fabrics are
easily deformed or stretched during wearing due to
their elastic characteristics. The fabric layer will
become thinner when it is worn next to skin and more
open spaces will be created for transmitting UVR in the
actual end-use. Moon and Pailthorpe22 found that there
is 15.5% elongation on average when fabrics are in con-
tact with the body and this caused a remarkable reduc-
tion of UPF. The increase of the UVR penetration is
almost linear with stretch.14 It can be anticipated that
the UV protection provided by the chemical approach
may not always be effective because of the actual wear-
ing condition of garments. Although darker shaded
clothing can provide better UV protection than those
with pastel colors, more infrared (IR) radiation is
absorbed and heat is generated simultaneously, whichmakes the wearers feel unpleasant under hot conditions.
Therefore, a balance between UV protection and ther-
mophysiological comfort is essential when developing
UV protective garments.
This paper aimed at studying the UV protection
property of knitted fabrics from a fundamental level
by considering how the modification of knitted fabric
construction can improve the UV protective ability of
fabrics, instead of using a chemical approach as a sec-
ondary level. Fabric construction is deemed to present
the simplest and cheapest solution to achieve good UV
protection without additional finishing processes.31
From the literature review, fabric construction has
been proposed as one of the most important variables
affecting UVR transmission, especially when light pastel
colored fabrics were used as UV protective clothing.14
Experimental details
Materials
In this study, 10 fabric constructions were examined
wherein four structures are single-knitted fabrics and
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the other six are double-knitted fabrics. Single-knitted
fabrics are knitted with one set of needles, whereas
double-knitted fabrics are knitted with two sets of nee-
dles, either rib or interlock gating. Different knitted
fabric constructions were designed based on the com-
bination of three basic knit stitches – knit, tuck and
miss stitches – which are shown in Figure 1. The yarn
path diagrams for the 10 constructions are illustrated
in Figure 2.
Fabric specimens were knitted using a Stoll CMS
822 14 G computer flat knitting machine using 100%
combed organic cotton yarn. Plied yarns were used
with the yarn count 3/40 s (three single yarns of
40 cotton counts were combined in the yarn feeding
to get a plied yarn). It is usual practice for knitwear
production to have plied yarns for knitting instead of
one single yarn with the same yarn count in order to
achieve higher strength, uniformity, better abrasion and
fabric appearance. The approximate yarn count for the
plied yarn is 42 tex and the calculated yarn diameter is
0.01 inch, according to the cloth geometry by Peirce33
and Booth.34
Apart from untreated greige fabrics, another set of
greige fabric specimens were scoured and bleached to
remove the natural pigments and impurities in order to
investigate the impact of bleaching against UV protec-
tion among various knitted fabric constructions. The
cotton knitted fabrics were scoured and bleached in a
Figure 2. Yarn path diagrams of different knitted fabric constructions.
Figure 1. Basic knit stitches viewed from the fabric face: (a) knit stitch; (b) tuck stitch; (c) miss stitch.
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combined process at laboratory conditions with 4 g/l
hydrogen peroxide, 6 g/l sodium hydroxide, 0.5 g/l sta-
bilizer and 0.5 g/l wetting agent. Hydrogen peroxide
was chosen as the bleaching agent to minimize the
damage on fabrics during the bleaching process.
Test methods
Assessment of ultraviolet protection factor
The UV protective ability of fabrics is commonly
expressed in terms of UPF. The UPF of fabric speci-
mens was measured using a Cary 300 Conc ultraviolet-
visible (UV-Vis) spectrophotometer equipped with an
integrating sphere and a Schott UG filter for minimiz-
ing any measurement error caused by fluorescence.
UPF measurement was conducted corresponding to
the Australian/New Zealand Standard AS/NZS
4399:1996.35 Fabric specimens were evaluated in a
dry, flat and tensionless state with measurements
taken in both machine and cross-machine directions
of the fabric. All fabric specimens were conditioned
under standard environment for 24 hours prior to
assessment.36 The transmittance over a wavelength
range of 290–400 nm with 5 nm intervals was measured
using the spectrophotometer for calculating the UPF of
fabric specimens using Equation (1):37,38
UPF ¼ E eff
E 0 ¼
P400nm290nm E S P400nm
290nm E S T ð1Þ
The UPF is defined as the ratio of the average effectiveUVR irradiance calculated for unprotected skin (E eff )
to the average effective UVR irradiance calculated for
the skin protected by test fabric (E 0), where E is the
relative erythemal spectral effectiveness, S is solar
spectral irradiance in Wm2 nm1, T is the spectral
transmittance of the fabric, is the wavelength in nm
and is the bandwidth in nm. Although definitions of
UVR and ultraviolet B (UVB) given in the standards
start at 280 nm, the measurement of UVR transmission
of the specimen records from 290 to 400 nm. The UVR
irradiance at wavelengths below 290 nm is not used in
the calculations because these wavelengths are unlikely
to reach the Earth’s surface.35 The inclusion of these
wavelengths in the calculations would preclude the use
of some otherwise acceptable spectrophotometers and
spectroradiometers.
Fabric thickness, weight and stitch density
Thicknesses of fabric specimens were measured corres-
ponding to the standard test method ASTM D1777-96
(Reapproved 2011).39 A calibrated digital thickness
tester with counter balance was used to measure the
thickness without distortion in a plane parallel to the
presser foot and anvil. Fabric weight was measured in
accordance with the standard test method ASTM
D3776-09 (Option C for small swatch fabric).40 The
stitch densities of fabric specimens were obtained by
counting the number of courses and wales to the near-
est half stitch. As there are rather complex fabric con-structions being assessed, such as rib, cardigan and
Milano, the wales and courses recognized on visual
inspection of the fabric may be made up of two or
more structures. The determination of the number of
stitches per unit area was acquired.
Porosity
Previous studies found that porosity is an important
indicator for UV protection performance of a
fabric.8,41–45 When UVR strikes the fabric, it can be
reflected, absorbed by fiber, scattered within the
fabric layer and transmitted through fibers and fabric
pores.18 The incident radiation passing through fabric
is largely dependent on the percentage of volume within
a fabric in which there is no fiber in that volume from
the fabric face to back.46 Therefore, the three-
dimensional nature of fabrics with various knit struc-
tures can be investigated by considering the fabric por-
osity instead of either fabric thickness or fabric weight
only. The more porous structure of the fabric will result
in a higher porosity, while a tighter structure gives a
lower porosity. Knitted fabrics usually have a higher
porosity than woven fabrics.47
Various methods of determining the porosity of porous materials were
firstly developed in the field of petroleum technology,
wherein the gravimetric method has been applied to
fabrics.44 Porosity can be defined as the proportion of
void space within the boundaries of a solid material,
compared to its total volume; in other words, it is the
fraction of void space in a porous medium.47–49
Porosity is usually expressed in percentage (%); the cal-
culation is shown in Equation (2):
PorosityðÞ ¼ 100 1 t
m ð2Þ
where t is the bulk density (g/cm3) and m is the fiber
density (g/cm3). The fiber density of cotton, 1.54 g/cm3,
was substituted in the equation for calculation.50 The
calculation of bulk density (g/cm3), t, of a knitted
fabric is obtained by Equation (3), where M is the
mass per unit area of fabric and V is the volume of
the unit area of fabric:51,52
t ¼M
V ð3Þ
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The volume of the unit area of fabric is simply equiva-
lent to the geometrical fabric thickness, t, and therefore
calculation of bulk density can be summarized as
Equation (4):51
Bulk Density ðg=cm3Þ ¼ M ðg=cm2Þ
t cmð Þ ð4Þ
Visual assessment on fabric pores
Different fabric constructions give a unique fabric sur-
face appearance as well as the size of fabric pores,
which determines the amount UVR transmission.
The fabric pores of greige and bleached knitted fabrics
with different structures were assessed visually through
the microscope under standard condition. A stereo
microscope Lecia M156C was used to capture the
micrographs with 25.0 magnification. The micro-
graphs of greige and bleached single-knitted fabrics
and double-knitted fabrics are shown in Figures 3and 4, respectively.
Analysis
In order to systematically study the impact of knit
structures and bleaching on the UV protective
Figure 3. Micrographs of greige and bleached single-knitted cotton fabrics at gauge length 14 G: (a) all knit; (b) knit & tuck; (c) knit &
miss (25%); (d) knit & miss (50%).
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Figure 4. Micrographs of greige and bleached double-knitted cotton fabrics at gauge length 14 G: (a) 1 1 rib; (b) half cardigan;
(c) full cardigan; (d) half Milano; (e) full Milano; (f) interlock.
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performance in relation to the structural parameters of
knitted fabrics, factorial analysis of variance
(ANOVA) was conducted. It identifies the existence
of significant differences in various variables studied,
which includes the UPF and fabric structural proper-
ties covering fabric weight, thickness, stitch density
and porosity among different knit structures. Any dif-ferences between the variables studied were considered
as significant if the p-value was less than or equal to
0.05. The interaction effect and main effect were iden-
tified among groups of variables. The effect size stat-
istics (partial eta squared) were examined to indicate
the proportion of variance of the dependent variable
that is explained by the independent variable.53
It reveals the relative magnitude of the differences
between means, or the amount of total variance in
the dependent variable that is predictable from know-
ledge of the levels of the independent variable.54 The
effect size can be classified as small (partial eta
squared ¼ 0.01), medium (partial eta squared ¼ 0.06)
and large (partial eta squared ¼ 0.14) according to
Cohen’s criterion.55 Post-hoc tests were performed
for a whole set comparison by exploring the differ-
ences between each of the fabric construction groups
in the study. Post-hoc tests compare each pair of
groups systematically and indicate whether there is a
significant difference in the means of dependent vari-
ables. Since single-knitted fabrics and double-knitted
fabrics have very distinct fabric constructions and
structural properties, their results are discussed and
analyzed separately to achieve a more accurate eluci-
dation. In addition, a paired-samples t-test was usedto compare the mean scores of the UPF and structural
parameters of the same groups of fabrics before and
after bleaching in order to determine the impact of
bleaching on the UPF and the structural parameters
studied.
Apart from analyzing the results by ANOVA, the
relationships between the UPF and the four struc-
tural parameters were explored by a correlation ana-
lysis. This determines the degree to which the
variables are related by using the Pearson correlation
coefficient (r). It is obtained from the correlation
analysis, which ranged from 1 to + 1, in other
words, from negative correlation to positive correl-
ation between two variables. The size of the absolute
value of r provides an indication of the strength of
the relationship. According to Cohen’s suggestions,
the strength of correlation can be divided into
three levels: small (r ¼ 0.10–0.29), medium (r ¼ 0.30–
0.49) and large (r ¼ 0.50–1.0).55 Preliminary analyses
were performed by generating a scatterplot for
each pair of variables to ensure no violation of
the assumptions of normality, linearity and
homoscedasticity.53
Results and discussion
The UPF and the main structural parameters – fabric
thickness, fabric weight, stitch density and porosity of
different knitted fabric structures – are shown in
Figures 5–9, respectively. The error bars in these figures
represent 95% confidence interval for variability of thedata collected.
Ultraviolet protection factor of single-knitted
cotton fabrics
The results of the ANOVA summarized in Table 1 indi-
cate that the UPF significantly differs among the four
single-knit structures (F 3,16 ¼ 79.824, p 0.05), greige
and bleached fabrics (F 1,16 ¼ 51.705, p 0.05) and
there is an interaction between knit structures
and bleaching (F 3,16 ¼ 23.346, p 0.05) affecting the
UPF. The effect sizes of knit structure (partial
eta squared ¼ 0.937), bleaching (partial eta
squared ¼ 0.764) and the interaction (partial eta
squared ¼ 0.814) are large. Although the existing inter-
action denotes that the structure of specimen was
affected by bleaching, the effect size of the knit struc-
ture is larger than bleaching, as well as larger than the
interaction effect. Most of the single-knitted fabric spe-
cimens exhibited a significant increase in UPF after
bleaching, except the all knit, as shown in Figure 5(a)
(t11 ¼ 2.73, p 0.05, two-tailed). Some studies
reported that bleaching caused an increase in UVR
transmission of cotton fabrics because of the removal
of natural pigments and lignin, which can absorb UVR;however, it should be noted that the fabrics studied
were mostly woven fabrics.8,42,43 Nevertheless, shrink-
age in the fabric caused by bleaching closed the small
gaps between yarns and resulted in less UVR
transmission.
The post-hoc test compares each pair of single-knit
structures and indicates whether there is a significant
difference in the means of the UPF. It shows that most
of the single-knit structures significantly differ from
each other ( p 0.05). The largest significant difference
in UPF for greige single-knitted fabrics exists between
the knit & miss (50%) (Mean ¼ 7.28, SD ¼ 0.37) and
knit & tuck (Mean ¼ 3.77, SD ¼ 0.29). The situation
changed after bleaching, with the largest difference in
UPF occurring between the knit & miss (50%)
(Mean ¼ 8.76, SD ¼ 0.54) and all knit (Mean ¼ 5.96,
SD ¼ 0.35). In general, single-knitted fabrics with knit
& miss structures offer a higher UPF than the all knit,
whereas the knit & tuck structure gives the lowest UPF
in the greige stage. The long straight float of miss stitch
reduces the elasticity of fabric by pulling the adjacent
columns of wale closer together and, thus, less open
spaces are present for transmitting UVR. The knit &
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miss (50%) has more miss stitches than the knit & miss
(25%) as well as higher UPF. The micrographs shown
in Figure 3(c) and (d) provide a comparison between
these two structures with a higher number of wales per
unit length in the knit & miss (50%) than that in the
knit & miss (25%) for both greige and bleached stages.
The knit & tuck incorporated with tuck stitches has a
lower UPF overall because the side limbs or legs of the
tuck loop are not restricted at the feet by the head of an
old loop and therefore the tuck loops tend to straighten
themselves, causing the loops in the adjacent wales to
be pushed apart. The presence of tuck loops made the
Figure 5. Ultraviolet protection factor (UPF) of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G
(with error bars): (a) UPF of single-knitted fabrics; (b) UPF of double-knitted fabrics.
Figure 6. Thickness of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G (with error bars):
(a) thickness of single-knitted fabrics; (b) thickness of double-knitted fabrics.
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fabrics bulkier and wider. Fabrics with knit & tuck
structures have a lower number of wales per unit
length with larger fabric pores, as shown in
Figure 3(b), than the other single-knit structures.
Ultraviolet protection factor of double-knitted
cotton fabrics
Both greige and bleached double-knitted fabrics have a
generally higher UPF (ranging from UPF 6.5 to 38.8)
than the single-knitted fabrics (ranged from UFP 3.8 to
8.8). Double-knitted fabrics are produced with two
sets of needles, with the second needle bed located at
a right angle to the first bed of needles. Hence, there is
one more layer of fibrous materials to absorb the UVR,
as well as greater the probability that the incident UVR
will encounter more fibers along its path.18 A general
comparison of UPF values for various double-knitted
fabric structures is shown in Figure 5(b). There are
significant differences between the UPF of the six
Figure 7. Fabric weight of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G (with error bars):
(a) fabric weight of single-knitted fabrics; (b) fabric weight of double-knitted fabrics.
Figure 8. Fabric stitch density of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G (with error
bars): (a) stitch density of single-knitted fabrics; (b) stitch density of double-knitted fabrics.
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double-knit structures (F 5,24 ¼ 5.348, p 0.05), the UPF
of greige and bleached double-knitted fabrics
(F 1,24 ¼ 516.202, p 0.05), and an interaction exists
between knit structures and bleaching (F 5,24 ¼ 21.325,
p 0.05), which influenced the UPF as shown in
Table 1. Contrary to the results of the single-knitted
fabrics, bleaching (partial eta squared ¼ 0.956) has a
greater influence upon the variance in UPF of double-
knitted fabrics than the knit structures (partial eta
squared ¼ 0.527) and also the interaction (partial eta
squared ¼ 0.816). The UPF of the six double-knitted
fabrics decreased significantly after bleaching
Table 1. Summarized results of the two-way between-groups analysis of variance (ANOVA) for ultraviolet protection factor (UPF)
and structural parameters of fabric specimens
Single-knitted fabrics Double-knitted fabrics
Dependent variables
Independent
variables F test p-value
Partial eta
square F test p-value
Partial
eta square
UPF Structures F 3,16 ¼ 79.824 0.000 0.937 F 5,24 ¼ 5.348 0.002 0.527
Bleaching F 1,16 ¼ 51.705 0.000 0.764 F 1,24 ¼ 516.202 0.000 0.956
Interaction F 3,16 ¼ 23.346 0.000 0.814 F 5,24 ¼ 21.325 0.000 0.816
Fabric thickness Structures F 3,16 ¼ 173.333 0.000 0.970 F 5,24 ¼ 76.091 0.000 0.941
Bleaching F 1,16 ¼ 3640.474 0.000 0.996 F 1,24 ¼ 1464.266 0.000 0.984
Interaction F 3,16 ¼ 26.298 0.000 0.831 F 5,24 ¼ 32.596 0.000 0.872
Fabric weight Structures F 3,16 ¼ 128.228 0.000 0.960 F 5,24 ¼ 473.943 0.000 0.990
Bleaching F 1,16 ¼ 2701.279 0.000 0.994 F 1,24 ¼ 1225.925 0.000 0.981
Interaction F 3,16 ¼ 15.053 0.000 0.738 F 5,24 ¼ 269.254 0.000 0.982
Stitch density Structures F 3,16 ¼ 308.314 0.000 0.983 F 5,24 ¼ 448.017 0.000 0.989
Bleaching F 1,16 ¼ 425.658 0.000 0.964 F 1,24 ¼ 77.63 0.000 0.764
Interaction F 3,16 ¼ 9.747 0.001 0.646 F 5,24 ¼ 14.214 0.000 0.748
Calculated Porosity Structures F 3,16 ¼ 45.958 0.000 0.896 F 5,24 ¼ 91.179 0.000 0.950Bleaching F 1,16 ¼ 0.292 0.596 0.018 F 1,24 ¼ 87.908 0.000 0.786
Interaction F 3,16 ¼ 7.423 0.002 0.582 F 5,24 ¼ 24.843 0.000 0.838
Figure 9. Porosity of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14G (with error bars):
(a) porosity of single-knitted fabrics; (b) porosity of double-knitted fabrics.
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(t17 ¼ 8.61, p 0.05, two-tailed), which is opposite to
the results of the four single-knitted fabrics. The results
here agree with previous studies, which stated that
bleaching causes more UVR to be transmitted through
the bleached cotton fabrics because of the absence of
natural pigments and impurities. The impact of shrink-
age for the double-knitted fabrics resulted from bleach-ing does not overcome the effect of bleaching, which
happened in the single-knitted fabric specimens.
Double-knitted fabrics are more dimensionally stable
and compact than single-knitted fabrics. The double-
knitted fabrics are unlikely to be stretched or deformed
during the process of bleaching. This conforms to the
results shown in Table 1 that there is a smaller effect
size of the interaction between bleaching and structures
(partial eta squared ¼ 0.816) than the effect of bleaching
alone (partial eta squared ¼ 0.956). The results of UPF
for the bleached double-knitted fabric specimens can be
explained with a more evident inference than the greige
double-knitted fabric specimens containing the natural
pigments and impurities.
The results of the post-hoc test show that most of the
double-knitted structures significantly differ from each
other ( p 0.05). The largest difference in UPF is found
between the greige half Milano (Mean ¼ 38.84,
SD ¼ 2.75) and greige interlock (Mean ¼ 25.85,
SD ¼ 1.61). After bleaching, the largest difference in
UPF is found between the bleached full cardigan
(Mean ¼ 6.52, SD¼ 0.31) and bleached interlock
(Mean ¼ 23.35, SD ¼ 0.51). The bleached interlock
obtains the highest UPF, followed by the bleached
Milano and bleached 1 1 rib, while the bleached car-digan possesses the lowest UPF. The interlock fabrics
are produced with interlock gating in which the col-
umns of wales are directly behind each other on both
the fabric face and back. They have a dimensionally
stable structure that does not tend to be stretched
easily. A compact structure in the interlock fabrics
can be observed from Figure 4(f), showing that adja-
cent columns of wale are packed closely together giving
a firmer fabric structure with less amount and smaller
size of fabric pores. However, fabrics other than the
interlock structure that were produced with rib gating
obtain a relatively lower UPF. In rib gating, the needles
of one bed are located in the spaces between the needles
of the other bed and the fabrics are more extensible in
the course-wise direction. The full Milano and half
Milano obtain the second-highest UPF after bleaching
because of the miss stitches incorporated in the fabric
structures. The only difference between the full Milano
structure and half Milano structure is that one more
course is knitted on the front needle and missed at
the back. There are more miss stitches in the full
Milano fabric structure than the half Milano, which
results in higher UPF. The cardigan fabrics possess
a lower UPF in the bleached specimens than the
Milano fabrics because the tuck loops in cardigan fab-
rics extend the fabric in the course-wise direction and
larger fabric pores are created, which are illustrated in
Figure 4(b)–(e). As there are more tuck stitches in the
construction of the full cardigan than that of the half
cardigan, the UPF of the bleached full cardigan is lowerthan the bleached half cardigan.
Fabric thickness of single-knitted cotton fabrics
The results of the ANOVA in Table 1 show that there
are statistically significant differences in fabric thickness
among the four single-knit structures (F 3,16 ¼ 173.333,
p 0.05), greige and bleached fabrics (F 1,16 ¼ 3640.474,
p 0.05) and there is an interaction between knit struc-
tures and bleaching (F 3,16 ¼ 26.298, p 0.05) affecting
the fabric thickness. The effect sizes of knit structure
(partial eta squared ¼ 0.97), bleaching (partial eta
squared ¼ 0.996) and the interaction between knit
structures and bleaching (partial eta squared ¼ 0.831)
are large. There is a significant increment of fabric
thickness among the four single-knit structures after
bleaching, as shown in Figure 6(a) (t11 ¼ 21.29,
p 0.05, two-tailed). The results of the post-hoc test
also reveal there are the largest differences in fabric
thickness between the greige knit & miss (50%)
(Mean ¼ 0.95, SD ¼ 0) and greige knit & miss (25%)
(Mean ¼ 0.82, SD ¼ 0.02), and also between the
bleached knit & miss (50%) (Mean ¼ 1.48, SD ¼ 0.01)
and bleached all knit (Mean ¼ 1.19, SD ¼ 0.01). In both
greige and bleached stages of fabrics, knit & tuck hashigher thickness than knit & miss (25%), but the results
in UPF for these two structures are reversed. Although
the miss stitches in the fabric construction can make the
fabric narrower in width, while tuck stitches increase
the width of fabric as well as the fabric thickness, the
fabric pores within the knit & tuck fabrics are larger
than the other knit structures, as shown in Figure 3(b),
and more UVR can be passed through the fabric pores
directly. It contradicts the general concept that a
thicker fabric can give better UV protection regardless
of the fabric structure and porosity.
Fabric thickness of double-knitted cotton fabrics
Double-knitted fabrics have the significant differences
in fabric thickness among the six double-knit structures
(F 5,24 ¼ 76.091, p 0.05), greige and bleached fabrics
(F 1,24 ¼ 1464.266, p 0.05) and interaction exists
between structure and bleaching (F 5,24 ¼ 32.596,
p 0.05). Knit structure (partial eta squared ¼ 0.941),
bleaching (partial eta squared ¼ 0.984) and the inter-
action between knit structures and bleaching (partial
eta squared ¼ 0.872) have large effect sizes. The overall
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thickness of double-knitted fabric specimens shown in
Figure 6(b) indicated the thickness increased signifi-
cantly after bleaching (t17 ¼ 12.03, p 0.05, two-
tailed). From the results of the post-hoc test, the largest
differences in fabric thickness are found between the
greige half cardigan (Mean ¼ 1.53, SD ¼ 0.06) and
greige 1 1 rib (Mean ¼ 1.23, SD ¼ 0.02), and alsobetween the bleached interlock (Mean ¼ 1.98,
SD ¼ 0.01) and bleached 1 1 rib (Mean ¼ 1.53,
SD ¼ 0.02). In the greige stage, the half cardigan has
the highest thickness, while the 1 1 rib possesses the
lowest thickness. However, the situation changed after
bleaching in which the bleached interlock obtains the
highest thickness and the bleached 1 1 rib has the
lowest thickness again. The interlock has the greatest
change in fabric thickness by 46.7% after bleaching,
which results in the variation in UPF of interlock fab-
rics, with the lowest UPF among structures in the
greige stage becoming the structure that possesses
the highest UPF after bleaching. This agrees with the
results in the effect size of bleaching in double-knitted
fabrics (partial eta squared ¼ 0.956), which has a
greater influence upon the variance in UPF than the
knit structures of double-knitted fabrics (partial eta
squared ¼ 0.527).
The correlations between UPF and fabric thickness
of single- and double-knitted fabrics in greige and
bleached stages are studied and the results are indicated
in Table 2. Positive correlations are found between the
UPF and the fabric thickness of bleached single-knitted
fabrics (r ¼ 0.821, p 0.05) and the bleached double-
knitted fabrics (r ¼ 0.6, p 0.05), which both have alarge strength of correlation (r ¼ 0.50–1.0). The higher
the thickness of bleached fabrics, the better UV pro-
tective ability obtained. However, this is not always
true when comparing different knit structures, such as
the bleached knit & tuck, with the second-highest thick-
ness but also the second-lowest UPF among the single-
knit structures. There are no significant correlations
between UPF and thickness of the greige single-knitted
fabrics (r ¼ 0.298, p ¼ 0.347) and greige double-
knitted fabrics (r ¼ 0.416, p ¼ 0.086). The variation in
fabric thickness of the greige single- and double-knitted
fabrics may not significantly affect the UV protection
performance because of the natural pigments and
impurities that absorb a certain amount of UVRalready.
Fabric weight of single-knitted cotton fabrics
Similar to the results of fabric thickness, the results of
the ANOVA in Table 1 indicate that the fabric weight
of single-knitted fabrics differ significantly in structures
(F 3,16 ¼ 128.228, p 0.05), greige and bleached fabrics
(F 1,16 ¼ 2701.279, p 0.05) and an interaction exists
between knit structures and bleaching (F 3,16 ¼ 15.053,
p 0.05) that has an impact on fabric weight. The effect
sizes of knit structure (partial eta squared ¼ 0.96),
bleaching (partial eta squared ¼ 0.994) and the inter-
action (partial eta squared ¼ 0.738) are also large.
There is an overall increment of fabric weight among
the single-knitted fabrics after bleaching, as shown in
Figure 7(a) (t11 ¼ 23.69, p 0.05, two-tailed). The
results of the post-hoc test show that the greige knit
& miss (50%) (Mean ¼ 184.49, SD ¼ 2.93) and greige
knit & tuck (Mean ¼ 153.58, SD ¼ 3.98) obtain the lar-
gest difference in fabric weight, and also between the
bleached knit & miss (50%) (Mean ¼ 280.25,
SD ¼ 3.87) and bleached all knit (Mean ¼ 224.03,
SD ¼ 4.43). Although the knit & tuck and knit & miss(25%) have similar fabric weights in both greige and
bleached stages, the UPF of the greige knit & tuck is
lower than that of the greige knit & miss (25%). Fabrics
with similar fabric weight do not have the resembling
UV protective performance because of the distinct
fabric structures and other factors, such as size of
fabric pores.
Table 2. Pearson correlation coefficients (r ) between the ultraviolet protection factor (UPF) and the structural
parameters of fabric specimens
Structural parameters
Single-knitted fabrics Double-knitted fabrics
Greige Bleached Greige Bleached
Fabric thickness 0.298NS 0.821a 0.416NS 0.600a
Fabric weight 0.702a 0.949a 0.242NS 0.958a
Stitch density 0.813a 0.142NS 0.044NS 0.713a
Calculated Porosity 0.896a 0.246NS 0.546a 0.812a
aThe correlation with the UPF is significant at the 0.05 confidence level.NSThe correlation with the UPF is not significant at the 0.05 confidence level.
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Fabric weight of double-knitted cotton fabrics
Similarly, there are significant differences in fabric
weight among the six double-knit structures
(F 5,24 ¼ 473.943, p 0.05), greige and bleached fabrics
(F 1,24 ¼ 1225.925, p 0.05) and an interaction exists
between structure and bleaching (F 5,24 ¼ 269.254, p 0.05). Knit structure (partial eta squared ¼ 0.99),
bleaching (partial eta squared ¼ 0.981) and the inter-
action between knit structures and bleaching (partial
eta squared ¼ 0.982) have large effect sizes. The overall
fabric weights of double-knitted fabric specimens are
shown in Figure 7(b) and most of them increased
after bleaching except the full cardigan (t17 ¼ 3.93,
p 0.05, two-tailed). This may be because of the loss
of fibrous material from the full cardigan during the
scouring and bleaching process resulting in weight
loss: further investigation is required in the future.
From the results of the post-hoc test, the greige inter-
lock (Mean ¼ 298.11, SD ¼ 1.29) and greige 1 1rib
(Mean ¼ 250.57, SD ¼ 2.76) have the largest difference
in fabric weight, as well as the bleached interlock
(Mean ¼ 430.14, SD ¼ 5.26) and bleached full cardigan
(Mean ¼ 241.66, SD ¼ 3.27). The bleached interlock
and Milano have relatively higher fabric weight than
the bleached 1 1 rib and cardigan because of the com-
pact structures where yarns are closely packed together
resulting in higher fabric weight.
From the results of correlation analysis shown in
Table 2, positive correlations are found between the
UPF and fabric weight of the greige single-knitted fab-
rics (r ¼ 0.702, p 0.05), bleached single-knitted fabrics(r ¼ 0.949, p 0.05) and the bleached double-knitted
fabrics (r ¼ 0.958, p 0.05). The strength of these posi-
tive correlations is large (r ¼ 0.50–1.0) according to
Cohen’s suggestion.55 With higher fabric weight, the
UPF of greige and bleached single-knitted fabrics and
bleached double-knitted fabrics can be enhanced.
However, there is insignificant correlation between the
UPF and fabric weight of greige double-knitted fabrics
(r ¼ 0.242, p ¼ 0.334). This can be confirmed with
Figures 5(b) and 7(b), which show that even though
the greige double-knitted fabrics have similar fabric
weights, their UPF results are quite distinct. The nat-
ural pigments and impurities in greige fabrics may be
the reason for the insignificant correlation resulted.
Double-knitted fabrics have a relatively more compact
structure than the single-knitted fabrics and there are
natural pigments and impurities encompassed in the
greige double-knitted fabrics. The fibrous material
and the natural pigments already absorb the UVR
effectively; therefore, variation in the fabric weight
does not have a great impact on the UPF. Fabrics
with similar weights but different colors or fiber con-
tents may exhibit very distinct UV protective ability,
which suggested that fabric weight is not the only
factor in explaining the UV protection of fabric.
Stitch density of single-knitted cotton fabrics
Significant differences in fabric stitch density are found
among the four single-knit structures (F 3,16 ¼ 308.31, p 0.05), greige and bleached fabrics (F 1,16 ¼ 425.66,
p 0.05) and the interaction between knit structures
and bleaching that influenced the stitch density
(F 3,16 ¼ 9.75, p 0.05), as shown in Table 1. All of
their effect sizes are large; knit structures (partial eta
squared ¼ 0.98) and bleaching (partial eta
squared ¼ 0.96) have similar effect size and both are
larger than the interaction (partial eta squared ¼ 0.65).
The shrinkage caused by scouring and bleaching
brought a significant increase in stitch density, as
shown in Figure 8(a) (t11 ¼ 11.11, p 0.05, two-
tailed). The results of the post-hoc test indicate that
the largest differences in stitch density are found
between the greige all knit (Mean ¼ 80.61, SD ¼ 1.06)
and greige knit & tuck (Mean ¼ 39.22, SD ¼ 3.03) and
between the bleached all knit (Mean ¼ 107.13,
SD ¼ 4.55) and bleached knit & tuck (Mean ¼ 53.01,
SD ¼ 3.49). However, insignificant differences in stitch
density are found between the bleached all knit and
bleached knit & miss (25%), as well as the bleached
knit & miss (25%) and bleached knit & miss (50%).
The knit & tuck has the lowest stitch density, while
the other three single-knit structures have a similar
stitch density because the tuck stitch widens the fabric
and results in fewer wales per length.
Stitch density of double-knitted cotton fabrics
Likewise, the results of the ANOVA in Table 1 show
that the stitch density of double-knitted fabrics differs
significantly in the knit structures (F 5,24 ¼ 448.017,
p 0.05), greige and bleached fabrics (F 1,24 ¼ 77.63,
p 0.05) and also there is an interaction between struc-
tures and bleaching that influenced the stitch density
(F 5,24 ¼ 14.214, p 0.05). The effect sizes of structures
(partial eta squared ¼ 0.989), bleaching (partial eta
squared ¼ 0.764) and the interaction (partial eta
squared ¼ 0.748) are large; the knit structure has
greater impact on stitch density than bleaching. Most
of the double-knit structures studied show a significant
increase in stitch density after bleaching (t17 ¼ 3.99,
p 0.05, two-tailed), except the half cardigan with an
insignificant decrease in stitch density. The cardigan
structures do not have obvious variation in stitch dens-
ity after bleaching when compared to the other four
double-knit structures, as shown in the micrographs
in Figure 4. The structure with tuck stitches is
generally less extensible in nature particularly to the
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double-knitted fabric, which has a compact fabric
structure. The results of the post-hoc test indicate the
largest differences in stitch density are found between
the greige half Milano (Mean ¼ 99.48, SD ¼ 1.15)
and greige full cardigan (Mean ¼ 30.95, SD ¼ 4.69),
and also between the bleached half Milano
(Mean ¼ 104.21, SD ¼ 4.35) and bleached full cardigan(Mean ¼ 30.93, SD ¼ 2.15). Although the half Milano
structure possesses the highest stitch density and there
are insignificant differences in stitch density among the
half Milano, full Milano and interlock, the UPFs
among them are quite different: the interlock has the
highest UPF among the six double-knit structures.
The results of the correlation analysis shown in
Table 2 reveal that significant positive correlations are
only found in the greige single-knitted fabrics
(r ¼ 0.813, p 0.05) and bleached double-knitted fab-
rics (r ¼ 0.713, p 0.05). These positive correlations
indicate the UV protection will be enhanced when the
stitch density of greige single-knitted fabrics and
bleached double-knitted fabrics increased. The greige
single-knitted fabrics have natural pigments and impu-
rities acting as natural UV absorbers and more UVR
can be absorbed when the natural UV absorbers in the
yarn are packed closer together. However, the greige
double-knitted fabrics already have a dense fabric
structure together with natural UV absorbers for block-
ing the UVR; therefore, the increase in stitch density of
greige double-knitted fabrics will not bring significant
impact to the UPF. After bleaching, the natural UV
absorbers were removed and therefore the fabric struc-
ture of bleached double-knitted fabrics becomes a moreparamount factor in explaining the variation in UPF
when the stitch density increases.
Porosity of single-knitted cotton fabrics
Porosity was found to be a major indicator for UV
protection of a fabric.8,41–45 The fabric construction
influences the pore size, pore distribution, pore con-
nectivity and total pore volume, and all of these proper-
ties of the macro-pore are important in determining
UVR transmission of a fabric.56 By studying the por-
osity of fabric, the fabric construction can be con-
sidered in a three-dimensional approach with the
structural parameters, thickness and weight (areal dens-
ity), fiber density and the void spaces within the fabric
layer included.
From the results of the ANOVA shown in Table 1, it
can be found that a statistically significant difference in
porosity is found among the four single-knit structures
(F 3,16 ¼ 45.958, p 0.05), but not between the greige
and bleached single-knitted fabrics (F 1,16 ¼ 0.292,
p ¼ 0.596). This reveals that bleaching does not have a
conspicuous impact on the porosity of single-knitted
fabrics, although there is an interaction between bleach-
ing and the single-knit structure (F 3,16 ¼ 7.423,
p 0.05). The effect size of knit structure (partial eta
squared ¼ 0.896) is greater than that of bleaching (par-
tial eta squared ¼ 0.018) and also the interaction
between knit structures and bleaching (partial eta
squared ¼ 0.582). There are insignificant increases inporosity for the single-knitted fabrics after bleaching
that are contrary to the previous structural parameters
studied (t11 ¼ 0.34, p ¼ 0.737, two-tailed), as shown in
Figure 9(a). Although there are significant changes in
fabric thickness and fabric weight for the single-knitted
fabrics, porosity has less variation after bleaching
because the shrinkage of fabrics in scouring and bleach-
ing caused increase in fabric weight and thickness
simultaneously.
The results of the post-hoc test indicate that the greige
knit & tuck (Mean ¼ 89.35, SD ¼ 0.11) and greige knit &
miss (25%) (Mean ¼ 86.97, SD ¼ 0.32) have the largest
difference in porosity, as well as the bleached knit & tuck
(Mean ¼ 88.42, SD ¼ 0.12) and bleached knit & miss
(25%) (Mean ¼ 87.29, SD ¼ 0.30). The porosities
among the other three structures, all knit, knit & miss
(25%) and knit & miss (50%), are not significantly dif-
ferent from each other in both greige and bleached
stages. The bleached and greige knit & tuck have
higher porosities than the other three single-knit struc-
tures because the presence of tuck stitches increases the
porosity of fabric due to the unique formation of a tuck
loop. Since a tuck stitch is formed when a needle takes a
new loop without clearing the previously formed loop
(held loop), the held loop together with the loop that joins (tuck loop) are accumulated on the needles and
eventually give a bulkier structure to fabrics with more
void space within the fabric layer. Although the four
single-knit structures have quite similar fabric thickness
and weight, they differ in stitch density and porosity
because of their distinct fabric structures. A fabric with
higher porosity represents its fabric structure, encom-
passing more void spaces or fabric pores; in other
words, it is a rather porous structure. The knit & tuck
structure is obviously more porous than the other three
single-knit structures, as shown in Figure 4, and also
reflects the result of lower stitch density, even resembling
the fabric weight and thickness. Fabric porosity is a key
factor for UVR transmission, as the incident light can
pass through the fabric pore directly.42 Therefore, the
knit & tuck fabric provides more void spaces for the
transmission of UVR through the fabric, resulting in a
lower UPF than other single-knit structures.
Porosity of double-knitted cotton fabrics
Double-knitted fabrics have significant differences in
porosity among the six double-knit structures
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(F 5,24 ¼ 91.179, p 0.05), greige and bleached fabrics
(F 1,24 ¼ 87.908, p 0.05) and an interaction exists
between structure and bleaching (F 5,24 ¼ 24.843,
p 0.05). The effect size of the double-knit structure
(partial eta squared ¼ 0.95) is larger than bleaching
(partial eta squared ¼ 0.786), as well as the interaction
between knit structures and bleaching (partial etasquared ¼ 0.838). Most of the double-knit structures
have significantly increased in porosity after bleaching,
as shown in Figure 9(b) (t17 ¼ 3.35, p 0.05, two-
tailed), but there is no remarkable variation in porosity
for half Milano fabrics after bleaching. The results of
the post-hoc test indicate there are the largest differ-
ences in the porosity between the greige half cardigan
(Mean ¼ 88.51, SD ¼ 0.66) and greige interlock
(Mean ¼ 85.66, SD ¼ 0.12), and also between the
bleached full cardigan (Mean ¼ 91.2, SD ¼ 0.08) and
bleached interlock (Mean ¼ 85.87, SD ¼ 0.25).
Similarly, the cardigan structures comprised of tuck
stitches have higher porosity than the other double-
knit structures. Tuck stitches create more void space
for the fabrics by pushing the neighboring wales further
apart, whereas miss stitches pull the wales closer
together, which diminishes the void volume contributed
by the interstices between the yarns. The interlock and
Milano fabrics obtain the lower porosity in both greige
and bleached stages, which conformed to the results of
higher UPF among the six double-knit structures.
Significant negative correlations between the UPF
and porosity are found in the greige single-knitted fab-
rics (r ¼ 0.896, p 0.05) and bleached double-knitted
fabrics (r ¼ 0.812, p 0.05), while the correlationbetween the UPF and porosity for the bleached
single-knitted fabrics is insignificant (r ¼ 0.246, NS)
as indicated in Table 2. The negative correlations
obtained for both greige single-knitted fabrics and
bleached double-knitted fabrics have large strength
according to Cohen’s suggestion,55 and the results
agree with previous results and discussion about the
presence of tuck stitches in the fabric structures leading
to an increase in porosity but reduction in UPF.
Although UPF and porosity of the greige double-
knitted fabrics are found to be positively correlated
(r ¼ 0.546, p 0.05), the strength of this correlation is
not as large as the previous negative correlations found.
Other factors may contribute to the UPF of the greige
double-knitted fabrics, such as the beige color of greige
fabric specimens, which absorbs the UVR. Deliberation
is required in the future works for exploring other
factors.
Conclusions
The UPFs are statistically different among various
fabric constructions with knit, tuck and miss stitches.
Generally, the fabrics incorporated with miss stitches
possess higher UPFs than fabrics with tuck stitches.
The greige single-knitted fabrics obtain higher UPFs
after bleaching, whereas the UPF of the double-knitted
fabrics decreased after bleaching. The effect size of
bleaching for the double-knitted fabrics is greater
than that for the single-knitted fabrics; therefore, knitstructures play a more important role in the variance of
the UPF than bleaching for single-knitted fabrics. It is
assumed that shrinkage of the single-knitted fabrics
caused by bleaching has a notable influence on the
UPF when compared with the effect of bleaching,
which removes the natural pigments and impurities.
In addition, the knit & miss (50%) fabrics and interlock
fabrics possess the highest UPF among the single-knit
and double-knit structures studied, respectively. The
micrographs provide a clear illustration of fabric con-
struction and fabric pores among different knit struc-
tures, which assist the explication of the effect of the
knit, tuck and miss stitches on UVR transmission.
Fabrics with high fabric thickness and weight do not
always give better UV protection. This is proven by the
knit & tuck structure, which has a lower stitch density
and higher porosity but similar fabric weight and thick-
ness to the other single-knit structures. Fabrics with
tuck stitches have larger fabric pores than the other
fabrics, which allow more UVR to pass through the
fabric directly.
The results of the ANOVA indicate that fabric
thickness, fabric weight and stitch density for both
single-knitted fabrics and double-knitted fabrics are sig-
nificantly influenced by bleaching and knit structureswith large effect sizes, as well as the porosity of
double-knitted fabrics. However, the porosity of
single-knitted fabrics is significantly affected by knit
structures, but insignificantly influenced by bleaching.
In addition, the results of correlation analysis reveal
that fabric thickness is positively correlated to UPF
for the bleached single- and double-knitted fabrics,
while fabric weight is positively correlated to UPF for
the greige and bleached single-knitted fabrics, as well as
bleached double-knitted fabrics. Nonetheless, the UPF
of double-knitted fabrics decreased while the fabric
thickness increased after bleaching. This indicates that
bleaching has a greater impact on UPF than fabric
shrinkage for double-knitted fabrics by removing the
natural pigments and impurities acting as natural UV
absorbers. Although various knit structures have simi-
lar fabric weight and thickness, the results of UPF and
stitch density are quite contrasting. Moreover, the fab-
rics with tuck stitches possess relatively higher fabric
porosity but lower UPF than the other structures for
both single- and double-knitted fabrics, because tuck
stitches give a bulkier structure to fabrics with more
void space for UVR transmission. This conforms to
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the negative correlation between UPF and porosity of
the greige single-knitted fabrics and the bleached
double-knitted fabrics.
Most of the single and double-knitted fabrics studied
do not have a high UPF that can be classified to be UV
protective (below UPF 15), except the greige double-
knitted fabrics with very good protection (UPF 25–39)and the bleached Interlock fabrics with good UV pro-
tection (UPF 15–24).35 Nevertheless, this paper pre-
sents a precursory study using cotton as the raw
material to investigate the impact of knit structures
and their respective structural parameters upon the
UPF. The project aimed to provide textile scientists
and technologists with a comprehensive and valuable
database for manufacturing UV protective light-weight
knitwear. Therefore, other factors contributing to the
UPF of knitted fabrics, such as fiber, color, wetness,
stretchability, chemical treatments or additives applied
on fabrics, as well as the relationships between these
factors and the UPF, will be researched in the future.
The results will enable textile manufacturers, designers
and users to select the most effective combinations of
variables from a range of fibers, fabric constructions
and textile wet processing agents for the production
of UV protective knitwear, and this value-added infor-
mation will bring significant benefits to the world wide
textile and clothing industry.
Funding
This work was supported in part by the General Research
Fund (grant number A-SA21) from the University Grants
Committee, Hong Kong and The Hong Kong PolytechnicUniversity, Hong Kong.
Acknowledgement
The authors would like to thank Prof. Ron Postle of the
University of New South Wales for his help and advice on
this research.
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