Photostability of HDPE Filaments Stabilized with UV
Absorbers (UVA) and Light Stabilizers (HALS)
Bhupendra Singh Butola, Ph.D., Mangala Joshi, Ph.D.
Department of Textile Technology, IIT Delhi, New Delhi INDIA
Correspondence to:
Bhupendra Singh Butola email: bsbutola@textile.iitd.ernet.in
ABSTRACT
HDPE monofilaments were photostabilized with
hindered a min e ligh t stabilizers (HALS) and UV
absorbers at varying stabilizer concentrations. The
filaments were assessed for UV resistance by exposure
to simulated outdoor weathering conditions in artificial
weathering apparatus and testing the exposed samples
at regular intervals for retained tensile properties. Films
of HDPE of varying thickness and containing different
concentrations of photostbilizers were also prepared.
The UV protective ability of the films was assessed by
measuring Ultra Violet Protection Factor (UPF). The
results indicate that UV absorbers improve the stability
of the filaments significantly. However, the best
performance was displayed by filaments containing
HALS.
Various approaches have been used to tackle this
problem. For protection of human skin, use of textiles
capable of blocking harmful UV radiation during
outdoor activity is finding increasing use. The other
approach is to use flexible woven/knitted structures
as sunscreen shelters made from UV stabilized
polymers for outdoor activities. The UV stabilizers
used in such applications have to perform twin tasks:
The polymer should have a good UV resistance for a
reasonably long service life and at the same time should
be able to block/absorb the harmful UVR to protect the
life and materials under the shelter.
The science and technology of UV stabilizers have
evolved over the years and today a wide range of UV
stabilizers are available commercially. However, the
Hindered Amine Light Stabilizer (HALS) class of
photostabilizers based on antioxidants, which were
developed over thirty years ago, offer excellent
performance
and
have
replaced
many
photostabilization systems [3-6]. Another class of
stabilizers, known as UV absorbers, acts by absorbing
UVR preferentially to polymers. The compounds
belonging to this class are generally used in
sunscreen lotions and UV protective textile clothing.
Keywords: Ultra Violet Protection Factor (UPF), U
V Absorber (UVA), Hindered Amine Light Stabilizer
(HALS), weathering, Ultra Violet radiation,
photostabilizer.
INTRODUCTION
The high energy of the solar radiation (200-400 nm),
generally known as Ultra Violet radiation (UVR) can
cause some undesirable effects in living creatures and
may also reduce service life of materials due to its
high energy. Almost a l l th e radiation of wavelength
below 290 nm is filtered out by the ozone layer in
earth’s atmosphere. The large doses, especially in the
short UVB range (280-315 nm) may cause sunburns,
skin cancer, photokeratitis, photodermatosis etc [1,2].
In addition to its deleterious effects on human beings, it
also deteriorates the material properties of apparel,
upholstery, draperies, carpets, furniture, paints,
electronic parts, building construction materials - wood,
plastic panels etc. and other articles of outdoor use and
limits their durability and life span. With the alarming
increase in the rate of ozone layer depletion in the
earth’s atmosphere, the risks involved due to prolonged
exposure to solar UV radiation are increasing day by
day. Hence it becomes imperative to protect the
human skin and other materials from harmful effects of
solar UV radiation.
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
It is observed that most of the reported literature on
development of UV resistant fibers and sunscreens is
in patent [7-9] form and not much research/scientific
studies on this development and analysis is available.
Hence in this study an attempt has been made to
develop UV stable HDPE monofilaments capable of
providing UV protection, by use of best available
photostabilizers and UV absorbers as additives. The
aim is to use mixture of these additives at different
ratios and to evaluate the performance of photo
stabilized HDPE filaments in terms of their durability
to UV radiation and their capability to provide UV
protection.
HDPE was chosen for the study as it is a commodity
polymer, easily available at economical price and easy
to process. Although pure PE should not absorb
61
http://www.jeffjournal.org
(Relene E 52009) was supplied by Reliance
Industries Limited with MFI of 50 and 0.9,
respectively. Carbon black (Superfine, 30% loading
in LLDPE) was provided by SCJ plastics, New Delhi.
above 180 nm and hence should not degrade in sunlight
[10] (solar radiation does not have light lower than 290
nm) the presence of chromophoric impurities in
commercial PE make it susceptible to sunlight. Due to
the presence of these moieties which may be
introduced during polymerization or processing as
carbonyl groups in the polymer (which absorb weakly
in 250 – 350 nm region), it starts to absorb UV light
and gradually degrades by autoxidation [11-13].
The degradation of polyethylene (HDPE, LDPE and
LLDPE) upon exposure to UV radiation has been
shown to manifest in alteration of mechanical and
physical properties and large chemical changes [14].
The exposure results in progressive cross linking and
chain scission [15] of the polymer. Initially, cross
linking may dominate which in some cases leads to
slight increase in stress at break; chain scission [16]
becomes dominant at later stages. Chemical changes
result in formation of vinyl groups and several
oxygenated functions like carbonyl, carboxyl and ester
groups [14, 17]. Generally most of the researchers have
focused on monitoring of carbonyl content for
assessment of polymer degradation, as it has been
shown to be directly related to mechanical and physical
property changes. In general, carbonyl content has
been shown to increase progressively with exposure
level [16, 18, 19].
The exposure to UV radiation results in loss in
mechanical properties like stress [20-21] and strain at
break; however the strain at break has been a preferred
parameter of study for many researchers. A gradual
deterioration in strain at break [21-23] initially and
sharp drop thereafter has been reported. While the
elastic modulus has been shown to increase
progressively [16, 20, 23] with exposure, development
of surface cracks [18, 24] has also been reported. In
thicker samples, the degradation has been shown to be
dependent on the thickness of the film/slab [25]. The
degradation occurs mostly on outer skin which is
supported by gradual decrease in carbonyl content [16,
21] as one moves to the center of slab. The inner
layers also have higher stress at break [16] as compared
to outer layers. Again, the energy of UV radiation has
an influence on the degree of deterioration. Higher
energy UV radiation (lower wavelength) causes more
degradation than lower energy radiation [26].
FIGURE 1. The structures and the code names of HALS and
UVAs used in the study.
Masterbatch Preparation
Master batches containing 5 wt % photostabilizer in
LLDPE were prepared on an SDL-Atlas F255A-D
laboratory mixing extruder from SDL International
(England). The extruder had automatic rotor and
temperature control with a variable speed of 5–260
rpm and a water-cooled hopper. The rotor and die
zone temperatures were kept at 160oC and the rotor
speed was fixed at 45 rpm. The extrudate was
quenched in water and cut to give masterbatch
granules.
HDPE Monofilament Preparation
UV stabilized HDPE monofilaments were prepared
by melt mixing and extrusion of HDPE and UV
stabilizer masterbatches in Laboratory
Extruder
(Betol, England).
MATERIAL AND METHODS
Material
Three HALS and four UV Absorbers used in this
study were supplied by CIBA Specialty Chemicals,
Mumbai. The structures and the code names used in
the study are shown in Figure 1. LLDPE (Reclair M
26500) and tape and monofilament grade HDPE
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
The
composition of stabilized
prepared is given in Table I.
monofilaments
The letter at I position and numeral at II position–
identify first additive.
62
http://www.jeffjournal.org
one minute residence time at 4-ton pressure and two
minute time at 7-ton pressure. After the 5-minute
cycle, the sheets were taken out from the press and
quickly quenched in running water to allow
solidification of the molten film. After cooling, the
films were removed from the press and tested for UPF.
Numeral at III position – denotes concentration of the
first additive.
Similarly next three positions identify second additive
and its concentration.
The letter at VII position identifies 1% carbon black.
Films of varying thickness were also prepared to
study the effect of film thickness on UPF.
The as spun monofilaments were drawn in two stages
as per the optimized drawing conditions given in Table
II.
Artificial Weathering
Exposure of the filaments was carried out in an
accelerated weathering chamber. The test standard
ASTM D 4355 – 84, Standard Test Method
for Deterioration of Geotextiles from Exposure to
Ultraviolet Light and Water (Xenon-Arc Type
Apparatus) was followed for accelerated weathering
in accelerated weathering equipment Xenotest Alpha.
The test parameters used are given in Table III.
TABLE I. The composition of stabilized HDPE monofilaments.
TABLE III. Test parameters for accelerated testing.
UPF Measurement
The UPF of the films was measured in M284 UV
Penetration Measurement System (SDL international
Ltd, UK). The measurements were done as per Test
Method AS/NZS 4399: 1996.
TABLE II. Optimized drawing conditions for drawing of as spun
monofilaments.
Tensile Testing
The tensile testing of the exposed and unexposed
samples was carried out on INSTRON universal
tensile tester, INSTRON, USA. Following test
parameters were used.
Film Preparation
Films of 200 µ thickness were prepared from as
spun monofilament granules in a laboratory press
(Carver, USA). The granules were spread uniformly
between two chrome plated stainless steel sheets and
required thickness was obtained by use of suitable
spacers between the sheets. Lower and upper platen
temperatures were set at 150oC each. After required
temperature was attained, the granules were between
stainless steel sheets and transferred to the press. A
two-minute residence time without pressure was given
for the granules to melt and flow. This was followed by
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
Gauge Length – 100 mm
Traverse speed – 30 mm/min
No of Tests per sample – 5
THEORY/CALCULATION
UV Protection
The UV protection provided by a material or structure
is generally measured in terms of its transmissibility
to UVR. This is then converted to Sun protection
factor (SPF) or Ultra Violet protection factor (UPF)
using the formula given below. The conversion of UV
transmissibility makes it easier to relate to the UV
protection provided by a material in objective terms.
63
http://www.jeffjournal.org
Sun Protection Factor (SPF)
or
TABLE V. The UPF values of HDPE films stabilized with 0.2 %
UV absorbers.
=
Ultra Violet Protection factor (UPF)
Where
E ‐ S

T
-
Relative erythemal spectral
effectiveness
Solar spectral irradiance, w/m2
Wavelength step, nm
Transmittance of the item, %,
measured in steps of 5 nm.
From the results it is clear that the relationship
between thickness and UPF is not linear. The value
of UPF increases sharply with film thickness and this
relationship between the UPF and thickness is
different for two different stabilizers.
RESULTS AND DISCUSSION
Criteria for Selection of UV Stabilizers
The stabilizers were used alone as well as in
combinations as they are known to show synergistic
effect. The concentrations of the stabilizers (except
Carbon Black) were varied in the range 0.1-0.3 wt % as
they are quite effective even at such low levels. To
reduce the number of compositions, the type and
concentration of the UV absorber was optimized on
the basis of its performance on HDPE sheets of 200µm
in terms of UPF value. The concentration of the UV
Absorbers was kept constant at 0.2% and the results are
given in Table IV.
TABLE IV.
The U PF values of 0.2mm thick HDPE films
stabilized with 0.2 % UV absorbers.
FIGURE 2. Variation of UPF for various UV absorbers with
thickness at 0.2 wt % content.
Since the UPF imparted to the HDPE was the
highest with UVA2, it was selected for use in
combination with HALS for synergistic effect. Carbon
black was also selected for the study and used alone at
different concentrations as well as in combination with
other stabilizers. The reason for its selection was its
effectiveness and economic price and in applications
where black color is not a constraint, it is a very
useful stabilizer.
Effect of Stabilizer Concentration on UPF of
HDPE Films
Similarly, the effect of the stabilizer concentration on
UPF of the HDPE films was also studied by preparing
the HDPE films of 0.2 mm thickness and increasing
concentrations of UVA2. The value of UPF is plotted
against concentration and shown in Figure 3. Again
it is clear from the figure that UPF of films increases
sharply with increase in stabilizer concentration. The
relationship between UPF and stabilizer concentration
in the film seems to be approximately linear.
Effect of Film Thickness on UPF of HDPE Films
Films of various thicknesses were prepared from HDPE
with the stabilizer concentration maintained at 0.2%.
The results are given in Table V and plotted in
Figure 2.
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
64
http://www.jeffjournal.org
the retained strength for different UV stabilizers varied
from 35 to 55% only. In comparison, the HALS
provided much better performance and the strength
retained after the same exposure time was much higher,
varying between 78 and 90%.
FIGURE 3. Variation of UPF with concentration (for UVA-2) at
200 μ film thickness.
Effect of Stabilizer Type and Concentration on the
Mechanical Properties of HDPE Monofilaments
All the monofilaments prepared by method described
in monofilament preparation section described above
and having compositions as per Table I were tested in
an artificial weathering chamber. The test parameters
are described in Table III. The samples were taken
out at regular intervals and evaluated for tensile
strength and elongation retained. The results are given
in Table VI.
FIGURE 4. Strength retention of monofilaments stabilized with
various additives upon exposure to accelerated artificial
weathering conditions.
TABLE VI.
Retention of strength and elongation of HDPE
filaments stabilized with various stabilizer systems after different
exposure times.
Another interesting observation that can be made from
the figure is that among the four UV absorbers tested,
UVA 3 provides the best strength retention (55%)
after the exposure for 1890 hrs. The remaining UVAs
(UVA1, UVA2 and UVA3) were almost identical in
terms of % strength retention. Although there was
significant difference in the UPF values obtained
using these additives, it does not reflect in the
stabilization provided to the HDPE filaments. Hence
it can be inferred that there is probably no correlation
between the ability of an additive to provide
protection from UV light (UPF value) and
stabilization (% retained strength).
As among the four UVAs the best stabilization was
provided by UVA3, it was selected for mixing with
various HALS in order to obtain possible synergistic
effect for stabilization of HDPE filaments. The
concentration of HALS was reduced to 0.2%.
It is evident that there is practically no loss of strength
in all cases at the end of 1890 hrs of exposure. This
was to be expected as the stabilization provided with
only HALS was quite high. This leaves little scope for
differentiation between the three types of HALS or
analysis of any kind of synergism between the two
types of stabilizers. A longer exposure time would
have brought out the differences between various
HALS.
The results shown in Table VI are selectively plotted in
Figure 4. Figure 4 depicts the strength retention of
HDPE monofilaments stabilized with UV Absorbers
and HAL Stabilizers. It is clear from the figure that
unstabilized HDPE filaments lose strength rapidly upon
exposure to artificial radiation and practically all the
strength is lost much before the 1000 h exposure time.
In comparison, UV Absorbers provide good short term
stability. However, at the end of 1890 hrs of exposure,
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
65
http://www.jeffjournal.org
The data indicates that at 0.3 % concentration level,
the UV absorbers used in the study provide a service
life of approximately 1400 hrs to HDPE filaments.
Since the UV absorbers act as photostabilizers
primarily by absorbing the UV radiation (which also
results in high UPF values of HDPE films, especially
with UVA2 and UVA3), it is logical to conclude that
loss in their effectiveness after long exposure hours
will also result in lower UPF values of stabilized
films. This means that polymers stabilized only with
UV absorbers not only lose mechanical properties but
also their ability to provide the UV protection with
time and this aspect is a cause for concern because at
some point of time such polymers would cease to
provide adequate protection without material actually
failing in terms of mechanical properties.. However,
UV absorbers are very effective stabilizers in thick
sections since decrease in the transmittance of light
absorbed increases exponentially with thickness
(Lambert’s Law) [27]. The inner middle layers
remain unaffected as most of the radiation is
absorbed by outer layers. However since the
filaments used in the study have a diameter in
the range 0.16-0.18 mm, UV absorbers were not very
effective when used alone.
Table VI also shows the effect of carbon black
concentration on the stabilization of HDPE filaments in
terms of strength retained. Again it is clear that there is
no loss in the strength of filaments after an exposure of
1890 hrs. Again, either a longer exposure time or lower
carbon black concentration would have been required
to reach a more definitive conclusion.
From the data in Table VI the following observations
can be made:
1.
Pure HDPE filaments lose more than one
third of its strength after 325 hrs of exposure. By 797
hrs it has lost practically all strength and becomes
brittle in the exposure rack itself.
2.
All the stabilized filaments provide good
stability till 797 hrs of exposure (retention of almost
90% strength) except the one stabilized only with
UVA4.
3.
By 1347 hrs, filaments stabilized only with
UV absorbers record a drop of approximately 30-50%
in strength and extension. At same exposure level,
filaments stabilized only with HALS show a drop of
only 10-20% only in strength.
4.
After 1890 hrs of exposure UV absorber
stabilized filaments show further drop in strength (4565%) and Elongation (35-60%). The drop at same
exposure level is only 10-20% for HALS.
5.
Filaments stabilized only with carbon black
and combinations of different stabilizers continue to
show very good stabilization against weathering even
after 1890 hrs of exposure. The maximum drop in
strength or elongation is around 10% only.
Hindered amine Light Stabilizers (HALS) being the
best UV stabilizers developed till date, provides a
much higher stabilization level to HDPE filaments as
compared to UV absorbers at the same (0.3%)
concentration level. More exposure is required to find
out the service life in case of HALS.
Carbon Black provides exceptional stability even at
1% concentration (recommended loading is 2-3%)
with almost 100% retention in strength and elongation
after 1890 hrs exposure. The only problem with
carbon black seems to be the black color imparted to
HDPE filaments, which may be a deterrent in some
applications.
Some useful insight about the effectiveness of the
stabilizer systems can be obtained from the analysis
of the data given in the table.
It would be helpful if some criteria can be formulated to
define the useful service life of the filaments. Since in
this study the effect of weathering on filaments is being
evaluated in terms of strength and elongation, the useful
service life of the filaments can be defined as the
exposure level in terms of radiation dose/exposure time
at which the filaments lose 50% tensile strength. The
logic in arriving at such a value lies in the fact that
most of the filaments had tenacity values higher than 6.
After 50% loss in strength the filaments would have a
tenacity value higher than 3, a safe level. This can then
be converted into years by comparing the radiation dose
thus obtained with average annual total solar radiation
dose recorded at any of the reference climatic locations.
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
The combinations of UVA2 at 0.3% concentration
with different HALS at 0.2, 0.3 and 0.4%
concentration levels also provides excellent
stabilization to HDPE filaments. Again the retention
in strength is almost 100% after 1890 hrs exposure.
Although higher exposure level is required to arrive
at more definitive conclusion, it can certainly be
argued that HALS and UV absorbers exhibit
synergistic property. Polymer degradation in U V
radiation occurs by formation of polymer peroxides
and polymer free radicals due to oxygen absorption[13].
These result in chain scission. While UV absorbers
66
http://www.jeffjournal.org
absorb most of UV radiation, there is less generation of
polymer peroxide and polymers radicals. HALS then
can deal more efficiently with these intermediates.
[3]
It can also be said that combination of HALS with
UV absorbers not only improves the life of filaments, it
also imparts UV protective property (UPF) to polymers.
The combination of UVA2, HALS and carbon black
also provides almost total stabilization till 1890 hrs of
exposure, which is obvious since carbon black alone is
very effective.
[4]
[5]
CONCLUSION
A range of HDPE monofilaments photostabilized
with different concentrations of UV Absorbers,
HALS, carbon black and their combinations in
various ratios were prepared and evaluated for
photostability to simulated solar radiation in an
accelerated weathering chamber. The concentration
of the UVAs and HALS varied in the range of 0.2-0.4
wt % and that of carbon black from 1 to 3 wt%. It
was observed that while neat HDPE filaments lost
almost all tensile strength at around 800 hours of
exposure, all photostabilized filaments retained
upwards of 90% strength at the same exposure time.
Filaments stabilized only with UV Absorbers show a
further drop of 30-50 and 45-65% in strength at 1347
and 1890 h exposure respectively whereas the drop is
10-20% only at similar exposure levels for filaments
stabilized with HALS. Hence it can be concluded that
while UV Absorber stabilized filaments lose strength
progressively with exposure to UV light, filaments
stabilized with HALS remain stable to UV radiation at
up to 800 h exposure time. However filaments
stabilized with neat carbon black (1-3 wt %),
combination of UVA, HALS and combination of
HALS, UVA and carbon black don’t show and drop
in strength even after 1890 h exposure.
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
One of the UV Absorbers (UVA-2) improved the UPF
value of HDPE film of 200 μ thickness to 135.
Hence, there is additional advantage of better UV
protection in terms of higher UPF in filaments where
UV Absorbers are also used along with HALS.
[15]
REFERENCES
[1]
Bajaj P. Kothari V K, Ghosh S B. Some
innovations in UV protective clothing. Indian J.
Fibre Text. Res 2000; 25; 315-329.
[2]
Bohringer B, Schindling G, Schon U, Hanke D,
Hoffman K, Altmeyer R, Klotz M L. UV
Protection by Textiles. Melliand International
1997;
3;
165-167.
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
[16]
67
Sedlar J. Petruy J, Pak J, Navratil M. Polymer
photostabilization by HALS derivatives: the
role of piperidine-hydroperoxide association.
Polymer 1980; 21; 5-7.
Gugumus F. The performance of light
stabilizers in accelerated and natural
weathering. Polym Degrad Stab 1995; 50;101116.
Geuskens G, Nedelkos G. The oxidation of
hindered amine light stabilizers to nitroxy
radicals in solution and in polymers. Polym
Degrad Stab 1987; 19; 365-378.
Toda T, Mori E, Murayama K. Studies on
Stable Free Radicals. IX. Peroxy Acid
Oxidation of Hindered Secondary Amines to
Nitroxide Radicals. Bull Chem Soc Jpn 1972;
45(6); 1904-1908.
Ishimoto Y, Hideo U. Light-Resistant Polyester
Fiber. JP 2008088607 (A) 2008.
Hong G. Moisture permeable anti-ultraviolet
rayon facing material and process technique
thereof. CN 101109128 (A) 2008.
Charles A G, Kowalski, L. UV and flame
resistant textile polymer yarn. U.S. Pat. Appl.
Publ. (2007), US 20070281158 A1.
Vasile, C, Degradation and decomposition,
Handbook of Polyolefins, II edition, 2000,
420-424.
Cicchetti O. Mechanisms of oxidative
photodegradation and of UV stabilization of
polyolefins. Adv Polym Sci 1970; 7; 70-112.
Carlsson D J, Wiles D M. Mechanisms of
oxidative photodegradation and of UV
stabilization of polyolefins. J Macromol Sci
Rev, Macromol Chem C1976; 14(1);65-106.
Gugumus F. Mechanisms of photooxidation
of polyolefins. Angew Makromol Chem
1990; 176/177; 27-42.
Severini F, Gallo R, Ipsale S. Environmental
degradation of LDPE observed by UV
spectroscopy.
Polymer
Degradation and
Stability 1993; 41; 103-107.
Mourad A H, Bouaza A, Dehbi A. Degradation
Assessment of LDPE Multilayer Films Used
as a Greenhouse Cover: Natural and Artificial
Aging Impacts. Journal of Applied Polymer
Science, DOI 10.1002/app.34928.
Hoekstra H D, Spoormaker J L, Breen J.
Mechanical and morphological properties of
stabilized and non-stabilized HDPE films
versus exposure time. Die Angewandte
Makromolekulare Chemie 1997; 247; 91-110.
http://www.jeffjournal.org
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
Guadgno L, Naddeo C, Vittoria V, Camino G,
Cagnani C. Chemical and morphological
modifications of irradiated linear low density
polyethylene. Polymer Degradation and
Stability 2001; 72; 175-186.
Kupper L, Gulmine J V, Janissek P R, Heise H
M.Attenuated total reflection
infrared
spectroscopy for micro-domain analysis of
polyethylene samples after accelerated ageing
within weathering chambers. Vibrational
Spectroscopy 2004; 34; 63–72.
Tidjani A, Arnaud R. Photo-oxidation of linear
low density polyethylene: A comparison of
photoproducts formation under natural and
accelerated exposure. Polymer Degradation
and Stability 1993; 39; 285-292.
Naddeo C, Guadgno L, Luca S D, Vittoria V,
Camino G. Mechanical and transport
properties of irradiated linear low density
polyethylene.
Polymer Degradation and
Stability 2001; 72; 239-247.
Yanai G, Ram A, and J. Miltz J. Accelerated
Weathering-Induced
Degradation
of
Unprotected Multilayer Polyethylene Slabs. I.
Journal of Applied Polymer Science 1995;
57; 303-310.
El-Awady M M. Natural Weathering, Artificial
Photo-Oxidation, and Thermal Aging of Low
Density Polyethylene: Grafting of Acrylic
Acid onto Aged Polyethylene Films, Journal
of Applied Polymer Science, 2003; 87; 2365–
2371.
Carrasco F, Pages P, Pasual S, Colom X.
Artificial ageing of high density polyethylene
by ultraviolet irradiation. European Polymer
Journal 2001; 37; 1457-1464.
Gulmine G V, Janissek P R, Heise H
M,Akcelrud L. Degradation profile of
polyethylene after artificial accelerated
weathering.
Polymer Degradation and
Stability 2003; 79; 385–397.
Barkhudaryan V G. Alterations of molecular
characteristics of polyethylene under the
influence of UV-radiation, Polymer 2000;
41; 5787–5791.
Gijsman P, Jan Hennekens J, Koen
J.Comparison of UV degradation chemistry in
accelerated (xenon) aging tests and outdoor
tests (II). Polymer Degradation and
Stability1994; 46; 63-74.
Lambert J H. Photometria sive de mensura et
gradibus luminis, colorum et umbrae,
Augsburg, Germany: Eberhardt Klett, 1760,
391-392.
Journal of Engineered Fibers and Fabrics
Volume 8, Issue 1 – 2013
AUTHORS’ ADDRESSES
Bhupendra Singh Butola, Ph.D.
Mangala Joshi, Ph.D.
IIT Delhi
Hauz Khas
New Delhi 110016
INDIA
68
http://www.jeffjournal.org