Water and Oil Repellent Finishing of Textiles by UV Curing
o
ples were dried at 80 C for 60s, and
finally irradiated in air by a static mer-
cury discharge UV lamp providing
three tunable irradiances: 146 mW/
cm2, 85 mW/cm2, or 67 mW/cm2.
Samples were exposed to the radia-
tion on one side for a time of 60 s. The
photoinitiator concentration was as-
sessed after previous tests aimed to
obtain the maximum grafting yield of
the oligomers in the adopted irradia-
tion conditions without stickiness on
the final fabric. It is worth to noting that,
by UV irradiation in air rather than in
nitrogen, the radical reactions are
slackened by oxygen interference,
hence a higher photoinitiator concen-
tration is needed to speed up the initi-
ation step. In fact, in the previous lab-
oratory experiments of irradiation in
inert atmosphere a 2 wt % photoinitia-
tor concentration on finishing agent
was enough to achieve satisfactory
grafting yields [2].
The flow diagram of the UV grafting
process is schematically depicted in
Figure 5. The thermal curing on refer-
ence samples was carried out follow-
ing the same diagram without photo-
initiator addition, while the irradiation
step was substituted by thermal treat-
o
ment in a hot flue at 150 C for 5 min.
Three samples for each process were
prepared for a statistical treatment of
data.
Water and oil absorbency were tested
by measuring the time it takes a drop
of liquid placed on the fabric surface
to be completely absorbed into the fab-
ric, according to AATCC/ASTM Test
Method TS-018 [21]. The contact an-
gles (CA) were evaluated by a CA ten-
siometer DSA20E (Krüss GmbH, Ham-
burg, Germany) equipped with a soft-
ware for drop profile fitting (Krüss
GmbH, Hamburg, Germany). The test
liquids used were HPLC-grade water
and paraffin oil (Sigma Aldrich, Milano,
Italy) with surface tension of 72 mN/m
and 31.5 mN/m, respectively. The con-
tact angles considered were the aver-
age of at least five measurements for
each sample with a standard deviation
of about 2–3%.Table 1: Absorbency of drops on treated samples
MethodFabricFinishing
AgentConc.
(g/L)Irradiance
(mW/cm2 )Water
(min)Oil
(min)
Thermal
ThermalPM
PMOleophobol
Pymasil50
40–
–>120
49>120
1
Thermal
ThermalCOT
COTOleophobol
Pymasil50
40–
–>120
34>120
1
UV
UVPM
PMOleophobol
Oleophobol50
2067
67>120
>120>120
>120
UV
UVPM
PMOleophobol
Pymasil20
10146
67>120
90>120
2
UV
UVCOT
COTOleophobol
Oleophobol50
5067
146>120
>120>120
>120
UV
UVCOT
COTOleophobol
Oleophobol20
2067
146>120
>120>120
>120
UVCOTPymasil4067801
Color measurements were carried out
by a Datacolor 110R reflectance spec-
trophotometer (Datacolor AG Europe,
Dietlikon, Switzerland), which enables
the determination of color differences
between a sample and a reference
through the formula:
(1)
whereare the
differences of lightness, chroma, and
hue respectively. For color tolerance
evaluation in textile industry, the CMC
(Color Measurement Committee) sys-
tem is currently used [22]. An ellipsoi-
dal volume around the position of the
color reference in the color space is
calculated as function of
If a sample fall inside the ellipsoid is
deemed acceptable, otherwise it is re-
jected. According to this system,
= 1 is assumed as limiting value un-
der which samples can be considered
to have the same color as the refer-
ence.
All measurements were then statisti-
cally evaluated by ANOVA with Minit-
ab 16 software (Minitab Inc., State
College, PA, USA), in order to point out
the most influencing parameters. The
plots obtained by this approach are
NCM-APRIL 2020
70reported in the Supplementary Materi-
al (SM).
Results and Discussion
The study about water and oil repel-
lent finishing has been performed on
the three fabrics of different composi-
tion and color. The main parameters
considered and varied, besides the
substrate, were the finishing agent and
the application process. Irradiance and
concentration of the finishing agent in
the impregnation solution, which are
directly related to the final add-on, were
the process parameters further inves-
tigated.
Obtained results were evaluated in
terms of absorbency of water or oil
drops on the treated surface, contact
angles (CA), and color measurements.
Absorbency of Water and Oil Drops
Absorption times of water or paraffin
oil drops, with a volume of about 10 L,
were evaluated on PM and COT sam-
ples treated by Pymasil or Oleophobol.
If the drop was not absorbed after 120
min, the test was stopped and the sub-
strate was considered completely re-
pellent toward the considered liquid.
Results and process parameters are
summarized in Table 1.