National Center for Radiation Research and Technology, Atomic Energy Authority, Egypt
*Corresponding author:
M.M.El Toony
Egypt, 3 Ahmad El-Zomr street
P.O.
Box 29- Nasr City, Cairo, 11370 Tel: 20166721956 Fax: +202 22 944 803 E-mail: Toonyoptrade@yahoo.com
Received November 03, 2011; Accepted January 19, 2012; Published January
26, 2012
Citation: El-Toony MM, El-Nemr KF (2012) Application of Acrylonitrile Butadiene
Rubber for Management of Industrial Waste Silica. J Material Sci Engg 1:104.
doi:10.4172/2169-0022.1000104
Some glass factories have drilled and milled silica mixed with water, their treatment depends on precipitation,
filtration etc. New concept for recycling of waste have paid attention to taking samples from different steps of
traditional treatment, water evaporation of samples have been carried out. Investigation of attained powdered using
EDX showed that, about 95.87% of sample was silica while particle size analyzer proved that it was not exceeding
73 micrometer. Silica powder mixed with Acrylonitrile Butadiene Rubber using miller and moreover thermal
compression were performed to achieve maximum compatibility and constant thickness of the composite. Electron
beam irradiation of the samples with different doses 25 and 100 KGy were carried out. Mechanical investigation
using stress strain technique, showing that pure silica composite was more than waste silica composite of step one
by small value. Thermal characterization was studied using thermal gravimetric analysis proved that improvement
of the silica waste / NBR composite than that of pure composite and also for electrical properties of the composite
which have the same behavior. These results confirmed application of waste silica instead of pure one with NBR
composites and management of environmentally problem such as water polluted with waste silica.
Polymer materials have served mankind for decades. They are
used in a wide range of industrial applications including packaging,
transportation, construction, pharmacy and the food industry world
wide. Elastomers are probably the most versatile and useful groups of
polymers ever known to man. These materials are used to manufacture
articles such as tires, isolation bearings, roofing sheets, seals, electrical
cables and hovercraft skirts. Raw elastomers, e.g. natural rubber (NR),
have poor properties and must be reinforced. Reinforcement gives
improvement in properties such as tear strength, abrasion resistance,
stiffness and hardness [1]. This is brought about by the inclusion of
solid particles for example carbon black. Fillers and curing agents to a
large extent control the technical properties of rubber compounds [2–8]. Particularly, as a chemical-free biomacromolecule, natural rubber
latex (NRL) has been used in manufacturing medical products such as
medical gloves, condoms, blood transfusion tubing, catheters, injector
closures and safety bags due to its excellent elasticity, flexibility,
antivirus permeation, good formability and biodegradability [9-11].
More recently, with the worldwide spread of the epidemic diseases
such as acquired immure deficiency syndrome (AIDS), hepatitis B,
severe acute respiratory syndrome (SARS) and avian influenza A
(H5N1), it becomes increasingly important and urgent to develop high
performance NRL protective products. Low tensile strength and poor
tear resistance are the other major drawbacks encountered in NRL
products, especially for medical gloves and condoms. Attempts have
been made to use carbon black [12], ultra-fine calcium carbonate [13],
modified montmorillonite [14], silica [15] and starch [1] to reinforce
dry NR or NRL. However, these traditional reinforcement materials are
not so effective for NRL. Therefore, it is essential to exploit new ways
to enhance the ageing resistance and mechanical properties for NRL
products. Further, such reinforcements are related to the secondary
structure of filler particles (agglomerate) [16–18] and the rubber/
filler interactions [19–21]. Silica is also known as an effective filler of
rubber reinforcement. Since silica does not have any radical and lone
electrons, it does not show any ESR signals. Thus silica filled rubber
systems are suitable for the investigation of chain scission of rubber
molecules during the deformation. For silica filled rubber systems,
the rubber/filler interactions can be controlled by the introduction of
coupling agent [22–24].
Tribological studies on SiO2 / acrylate nanocomposites show that
friction leads to the gradual loss of SiO2 nanoparticles [25]. In the
case that SiO2 nanoparticles are applied in tires, one may expect them
to be released by wear. It has been shown that many of the particles
released by the interaction between tires and road pavement are
<100 nm [26,27]. Furthermore, nanoparticles may be released when
nanocomposites are subjected to wear, such as sanding in the case of
coatings and abrasive use in the case of dental fillings [28-30]. Thus, it
would seem proper to consider the impact of nanoparticlate TiO2 and
amorphous silica after release. There is evidence that amorphous SiO2
nanoparticles may be hazardous to humans [31–33] and may exhibit
ecotoxicity [34]. A main molecular mechanism of cytotoxicity in case
of both amorphous SiO2 and TiO2 nanoparticles in the absence of
light appears to be oxidative damage linked to reactive oxygen species,
whereas TiO2 particles exposed to light and/or UV radiation may also
damage cells due to photo catalytically enhanced oxidation [35-44].
Changes of the nanoparticulate surface, which may be introduced to
achieve a better performance of nanocomposites e.g. [45-48], may in
turn affect hazard. All in all, amorphous SiO2 and TiO2 nanoparticles
can be hazardous, with actual hazard to a considerable extent
dependent on surface characteristics and in case of TiO2 also on crystal
structure. Claims that nanocomposites are ‘environmentally safe’ [49-50], ‘environment(ally)-friendly’ or ‘eco-friendly’ and that TiO2
nanoparticles are ‘non-toxic’ do not seem to have a firm foundation
in empirical data. Moreover, traditional methods of particulate control
such as wastewater treatment plants and filters are often not well suited
to efficiently catching TiO2 and SiO2 nanoparticles. There is only very
limited research into the performance of recycled nanocomposites
which contain organic polymers. One study has considered recycling
of layered silicate-thermoplastic olefin elastomeric nanocomposites,
focusing on mechanical performance [51]. In this study it was found
that though degradation of the nanocomposite during recycling
occurred, mechanical properties remained significantly better than
those of the neat polymer. More in general one might expect that the
oxidative properties of titania and silica nanoparticles are conducive
to polymer degradation and will increase thermal degradation over
the level occurring in neat polymer when recycling involves heating
[45,52,53].
Our results aims to manage the silica waste resulting from
manufacturing of glass crystals. The silica waste has different particles
size which used as filler with synthetic rubber to improve their
mechanical characteristics. Irradiation with electron beam has applied
to achieve compatibility and finally cross-linking. Thermal behavior of
waste silica / NBR composites have been studied and compared with
that of pure silica to show its availability to replace with them.
Experimental Approach
Materials and methods
Materials: A commercial grade acrylonitrile-butadiene rubber
(Europrene N3345) with 34 % acrylonitrite content was used as the
matrix polymer it was purchased from Enichem Company INC., Italy.
The recipe of this study contained also other additives, namely: ZnO,
stearic acid (from El-nasr Phosphate Company (Egypt). Pentaerthenol
triacrylate (PETriA) from Aldrish (Germany) used as sensitizer. The
first two additives act as accelerators as well as activators and their
content was 5 phr and 1 phr, respectively.
Diagram showing the formula of NBR
Sample Preparation: NBR, ZnO, stearic acid and silica followed
by sensitizer were mixed on a rubber mill (300 x 470 mm). The blends
composite sheets were then compression molded into sheets of 4
mm thickness at 160°C under a pressure of for 10 min. Irradiation by
Electron beam accelerator was carried out for achieve optimum com.
Powdered characterization
EDX Measurements: Oxford-tests attached to Scan Electron
Microscope (SEM), Joel- 5400, Japan.
Calibration data:- Gain factor: 49.996, Live time: 80 Seconds.
Sample data:- Total spectrum count: 875722, Live time: 70 Seconds,
System resolution: 173 eV, Accelerating voltage: 20.00 KV.
Particle size analyzers: The particle size analysis for different types
of silica was carried out by using Quantachrome porosimeter (Pore
Master 60) from Florida, (USA) depending on automatic mercury
intrusion under high pressure 60, 000 psia.
Mechanical properties measurements
Tensile measurements: Five individual dumbbell-shaped
specimens were cut out from the sheets using a steel die of standard
width (4 mm). The minimum thickness of the test specimens was
determined by gauge graduated to one hundredth of the mm. A bench
mark of 1.5 cm was made on working part of each test specimen. The
ultimate tensile strength and elongation at break point were determined
at crosshead speed 500 mm / min on a rubber tensile testing machine
Instron Machine model 1195, (England). The measurement was carried
out according to (ASTM D-412-66T), in which the standard deviation
was ±5%.
Electrical properties
AC impedance spectroscopy measurements over a frequency of 106
Hz using a system 3532 Hioiki bridge LCR hi tester. Each composite
sample was cut into sections 2.5 cm × 2.0 cm prior to being mounted
in the cell.
Thermal Properties measurements
Thermal Gravimetric Analysis: Shimadzu TGA -50, Japan, was
used to characterize the thermal stability of the different composites.
Thermal analysis was carried out using a thermal gravimetric analysis
(TGA) apparatus, samples of 0.98 - 1.5 mg were encapsulated in
aluminum pans and heated from 50 up to 500°C at heating rate 10°C
/min.
Results and Discussion
Silica powdered characterization
Chemical characterization of waste silica and pure by EDX
(Table 1): It is apparent that waste silica of step one contain 95.87 %
silica which is less than pure silica by 2.19 %. it has traces of aluminum,
sulfur, titanium, copper, zinc and tin while the la tter 4 elements have
disappeared completely in pure silica. Silica of step two differ from that
of step one by raising of aluminum concentration to about 16% which
is due to adding of alum to clarify the silica- water suspension as this
drilled silica is desired to get ride off. Metal traces of step two silica such
as titanium has about double value of step one while copper and zinc
are triple time of step one. Tin have disappeared completely in silica of
step two while sulfur has the same value in step one and step two. Silica
of step two has 79.09 % value of its weight so it decreased by 18.97 %
from the pure silica.
Table 1: Constituents of pure silica and waste silica taken from 2 steps of waste
treatment.
Particle size analyses of the silica (waste and pure one) (Table 2): As it seen from table 2 waste silica of waste silica of step one and two is
larger than pure silica while silica of step two (73 μm) is larger than that
of step one (66 μm). It may due to adding alum have important role for
precipitation of more silica particles have larger and smaller particle
size. Particle size of step two has larger particle size which may due to
different traces of metals by higher ratio than that of step one waste
silica. The included trace metals included higher atomic radius than
pure silica besides their ability to form a complexes such as aluminum.
Aluminum has a capability to react with acids and alkali which raise
their probability to form higher particle sized compounds. Surface area
of waste silica particles are varied with a large range compared to pure
silica.
Table 2: Particle size of pure and waste silica.
Rubber composite characterization
Nitrile butadiene rubber (NBR) is a family of unsaturated
copolymers of 2 propenenitrile and various butadiene monomers
(1,2-butadiene and 1,3 butadiene). Although its physical and chemical
properties vary depending on the polymer’s composition of nitrile (the
more nitrile within the polymer, the higher the resistance to oils but
the lower the flexibility of the material), this form of synthetic rubber is
generally resistant to oil, fuel, and other chemicals. Its resilience makes
NBR a useful material for disposable lab, cleaning, and examination
gloves. It is used in the automotive industry to make fuel and oil
handling hoses, seals, and grommets. NBR’s ability to withstand a
range of temperatures from −40°C to +108°C makes it an ideal
material for extreme automotive applications. Nitrile butadiene is also
used to create moulded goods, footwear, adhesives, sealants, sponge,
expanded foams, and floor mats. Nitrile rubber is more resistant than
natural rubber to oils and acids, but has inferior strength and flexibility.
Nitrile gloves are nonetheless three times more puncture-resistant than
rubber gloves [54]. Nitrile rubber is generally resistant to aliphatic
hydrocarbons. Nitrile, like natural rubber, can be attacked by ozone,
aromatic hydrocarbons, ketones, esters and aldehydes.
When nano or micro particles are dispersed with polymers, a core
shell structure tends to be formed in which nanoparticles covered with
polymeric chains under certain conditions such as those used for selfassembly.
By employing this approach, Caruso et al. [55] developed
core-shell materials with given size, topology, and composition.
Han and Armes [56] and Rotstein and Tannenbaum [57] studied
polypyrrole, polystyrene and silica nanocomposites, respectively,
and also confirmed the formation of this core-shell structure. In the
present study, SiO2 nanoparticles act as cores or templates to adsorb
NBR particles to develop a bulk NBR/SiO2 microcomposite. There is
electrostatic adsorption stage in this process figure 1 [58]. Electron
beam irradiation play very important role in cross linking of NBR and
silica; irradiate the composite make a homolitic and heterolytic fission
upon NBR rubber which firstly surrounded the silica mechanically and
thermally. Positive charged arising by irradiation on NBR adsorbed
on negatively charged silica powdered. Positively charged trace metals
which have investigated by EDX may play an important role for tightly
compatiblization to NBR especially waste silica taken from step two
(Figure 1).
Figure 1:
Mechanical properties of rubber composites
Hardness properties: Hardness and 300% modulus of all
vulcanizates are illustrated in table 3. As expected, the gum gives the
lowest hardness and modulus while hardness and modulus increase
noticeably when pure silica is added to the NBR. At 40 % amounts of
filler, step one vulcanizate exhibits nearly equal stiffness with waste silica
step two silica-filled composite. In addition, the results showed that
small difference of hardness between step one waste silica composites
when it compared with composite of pure one. Hardness of composite
increased upon 100 KGy irradiation using Electron beam irradiation as
it seen in table 3. This is thought to be due to the decrease in crosslink
density when high silica loading is used at 25 KGy. In a previous
study, crosslink density of NR vulcanizates gradually decreases when
silica loading is more than 20 phr [59]. The explanation is given as the
adsorption of zinc complex on the silica surface, thus lowering the
sulfur vulcanization efficiency. (Table 3)
Table 3: Study of hardness of pure and waste silica /NBR composite.
Stress strain of rubber composite (Figure 2) (Table 4): It is well
known that the stress–strain curves for silica filled rubber systems
are affected by the crosslink density of rubber matrix [60,61], the
size of agglomerates formed by the silica [62,63] and rubber / silica
interactions [64,60]. These effects can be controlled by the contents
of curing agents, the number of silanol groups on silica particles and
the introduction of coupling agent. Irradiation by electron beam have
advantageous role for cross linking and so on composite stress strain.
Waste silica composites have improved mechanical character than that
of pure one which represented by two samples first of which (sample
1) irradiated by 25 KGy. While second one which irradiated by 100
KGy was termed sample 4. The irradiated samples with 100 KGy dose
have higher stress value while that irradiated with 25 KGy have higher
strain value it may due to incomplete cross linking between inorganic
particles and the rubber understudy. These results may be explained
by higher cross-linking have attained by higher irradiation dose in the
range of 100 KGy.
Table 4: Study of tensile of pure and waste silica /NBR composite.
Electrical behaviors of rubber composite: The dielectric behavior
of composite materials can be also changed depending on the particle
size of the added particles. Some degree of dielectric enhancement was reported for composite materials with dispersed Al2O3, SiO2,
TiO2 particles as the particle size decreases from a typical bulk value
to a nanometer scale [65,66]. The dielectric differences between
nanometer-sized and bulk-sized particles can be seen in the Cole-
Cole plot. The dielectric enhancement is attributed to the dipoles
associated with the interfaces of the nanometer-sized particles, which
are created because of the presence of dangling bonds, twisted bonds or
bonds with adsorbed foreign molecules. In the case of heterogeneous
systems, where materials of different electrical properties contact each
other, the charges at the interfaces can additionally build-up [67]. For
the investigated systems such dipoles can result from the rubber-filler
ionic interactions when silica was used. Therefore we assume that the
concentration of dipoles present in the system varies with the amount
of added silica, that is reflected by the relaxation strength, Δε = ε0 –
ε∞ calculated from Cole-Cole plots for α- relaxation. The highest value
of the relaxation strength was obtained for the vulcanizates filled with
silica synthesized from 40% of silica, as one would expect as shown
in table 4. Therefore, this behavior could result from the highest
amount of silica, charges on its surface and its interactions with rubber
chains. The Cole-Cole plot for the investigated systems demonstrates a
major deviation from semicircle, especially at low frequencies, which
indicates not only a large distribution of relaxation times, but can be
also due to the presence of nanometer size particles. The differences
in the positions of Cole-Cole for the investigated systems could be the
result of the volume fraction of particles as well as the distribution of
the particles morphology, shape or structural interactions. Irradiation
dose has an important role for composite compatiblization 100 KGy is
advantageous dose over 25 KGy and so electrical conductivity is less in
larger dose. Pure silica/NBR composite is less in EC comparing to that
of waste silica composite. Waste silica of step two is higher in EC than
waste silica step one composite which may due to more concentration
of trace metals in this composite as it seen in table 4. (Table 5)
Table 5: Study of Electrical conductivity of pure and waste silica /NBR composite.
Thermal behaviors
Thermal gravimetric analysis (Figure 3): The thermal and thermo
oxidative ageing resistance of NBR / SiO2 composite can be assessed,
respectively, from the investigation of thermal and thermo oxidative
decomposition. There is only one obvious thermal decomposition step
of NBR molecular chains, primarily initiated by thermal scissions of
C–C chain bonds accompanying a transfer of hydrogen at the site of
scission.
Figure 3: Thermo-gravimetric analysis of NBR/ silica composites.
40 % pure silica – Nitrile butadiene rubber composite have
differentiated into 5 divisions as seen in figure 3. Each division could be
expressed on loss of some fragments of the composite (as CO, CO2, CH4,
H2O…etc). First division showed loss of 1.85 % of the original weight
by raising the temperature to 269°C expressed on working temperature
which may be explained by loss of water content included through the
composite. Second division illustrated gradual low decrease of weight
which was 3.5 % from the original value due to heating into 382°C. The
third division described convex curve, loss of weight through which
was 17 % by increasing the temperature to 438°C. 48 % weight loss was
observed via the fourth divisions which have occurred by raising the
temperature into 477°C which may due to loss of the majority of the
organic fragments. The fifth division illustrated the tail of the thermo
gram which ended at 484°C and the weight loss reached to 65 % of the
original weight.
Figure 3b and illustrated thermo gram of waste silica of 40 % ratio
with NBR forming a composite. The thermo gram attained could be
characterized into 4 divisions. First division showed 1.85 % loss of
weight by raising the temperature into 357°C and 373°C for the first
and second steps of silica/ treatment respectively. This loss of weight
described working temperature of the composite that proved their
availability with wider range of temperature than pure silica-NBR composite. While second step waste silica-NBR composite has more
thermal stability than step one waste silica-NBR composite. The
second division showed 16.5 and 16 % loss of weight by heating the
composite to 433°C and 435°C for step one silica silica composite and
second one in regular manner. There were dramatic weight decrease
ended at 47.5 % for the first step waste silica-NBR composite and
52 % weight decreased was attained by the second step waste silicarubber
composite. This division (Third division) attempt more thermal
stability of the first step waste silica / NBR composite than that of
step one’s silica composite. The fourth division described weight
loss which ended at 65 % weight loss from the original value for the
two thermograms by heating the temperature into 586°C. The two
thermograms attempt more compatibility of waste silica than pure one
through the composite with NBR.
Conclusion
This work aims to examine the availability to replace pure silica
used for NBR reinforcement by waste silica discharged from glass
and crystal factories. This study managed two problems, first of which
to overcome a serious environmentally one. The second problems
depend on cost benefit point of view, through which it could be using
no cost waste silica instead of somewhat expensive pure one. This
study included evaporation silica suspension to attain silica powdered
which have particle size in the range of 50 to 75 micrometer. Mixing
the attained silica powdered from two points of waste silica discharges
with nitrile butadiene rubber in the ratio of 40 %. Electron beam
irradiation with different doses (25 and 100 KGy) was exposed on
the composites for achieve optimum compatibility and finally crosslinking.
100 KGy irradiation dose have better results than 25 KGy.
Mechanical properties showed more or less change of tensile strength
and hardness by comparing pure silica composites by waste silica one.
Thermal and electrical characterizations of the waste silica composite
were improved. The attained results confirmed using the waste silica
instead of pure one for reinforces NBR to carry out composites having
different applications.
References
Dunnom DD (1968) Use of reinforcing silicas. Rubber Age 100: 49–57.
Rotstein H, Tannenbaum R. Baraton MI (2003) Synthesis, functionalization and surface treatment of nanoparticles. Stevenson Ranch: American Scientific Publishers 103–26.
OMICS Publishing Group is the member of / publishing partner of/source content provider to
OMICS Publishing Group, An Open Access Publisher and Scientific Events Organizer for the Advancement of Science & Technology. All Published content, except where otherwise noted, is licensed under a Creative Commons Attribution License
Please ensure that you are using the latest version of Adobe reader. If you do not have this software installed on your system, you can download the free Adobe Reader by simply clicking on the following link: http://www.adobe.com/products/acrobat/readstep2.html
