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'' Thermal and Mechanical Properties of polymeric composites
loaded with waste materials''
Presented by
Marwa mahhmoud Ibrahim abd el kader
الخواص الحرارية و الميكانيكية لمتركبات بلمرية محملة ببعض "
"المخلفات
إعداد
القادرمروة محمود ابراهيم عبد
VII
List of Tables
Page
Table (2-1): the composition of sample of NR with
different phr of recycled rubber to get (W-group) of
samples.
43
Table (2-2): the composition of sample of NR with
different phr CaCO3 to get (M-group) of samples.
44
Table (2-3): the composition of sample of NR with
different phr foaming agent to get (F-group) of samples.
45
Table (2-4): the composition of sample of NR with
different phr foaming agent+ CaCO3 to get (S-group) of
samples.
46
Table (3.1): The porosity values which give good fitting
for foamed NR and CaCO3/Foamed NR groups.
69
Table (3.2): The variation of crosslink densities as a
function of concentration for four groups of samples.
97
Table (3.3): The comparison between parameters of the
two optimum samples is summarized
104
Introduction & literature survey Chapter 1
1
1.1 Introduction
Thermal insulation is the method of preventing heat from escaping a
container or from entering the container. In other words, thermal insulation can
keep an enclosed area such as a building warm, or it can keep the inside of a
container cold. Heat is transferred from one material to another by conduction,
convection and/or radiation. Insulators are used to minimize that transfer of heat
energy. In home insulation, the R-value is an indication of how well a material
insulates (1)
.
Building insulation refers broadly to any object in a building used as
insulation for any purpose. While the majority of insulation in buildings is for
thermal purposes, the term also applies to acoustic insulation, fire insulation,
and impact insulation (e.g. for vibrations caused by industrial applications).
Often an insulation material will be chosen for its ability to perform several of
these functions at once
Thermal Insulation in buildings is an important factor to achieving
thermal comfort for its occupants. Insulation reduces unwanted heat loss or gain
and can decrease the energy demands of heating and cooling systems. It does
not necessarily deal with issues of adequate ventilation and may or may not
affect the level of sound insulation (2)
.
. In a narrow sense insulation can just refer to the insulation materials
employed to slow heat loss, such as: cellulose, glass wool, rock wool,
polystyrene, urethane foam, vermiculite, and earth or soil. But it can also
involve a range of designs and techniques to address the main modes of heat
transfer - conduction, radiation and convection materials. (3, 4)
The continuous development of the industry made it very important to
have information about new materials whose properties have never been
Introduction & literature survey Chapter 1
2
measured experimentally. Polymers play a very important role in the modern
society it difficult to imagine a branch of industry where it would be possible to
do without polymers especially the novel materials with previously unknown
properties.
In 1839, Charles Goodyear discovered that the addition of sulfur to raw
rubber could dramatically improve properties. The discovery of sulfur
vulcanization changed the rubber from a thermoplastic, which can be
reprocessed many times, to a thermoset, which can be shaped only once. Sulfur
vulcanization is used in current automotive tires in order to give the desired
properties and can meet the requirements for automotive tire applications.
The largest volume of thermosetting polymers in the waste stream is
generated by scrap tires. One approach to the successful reuse of recycled tire
rubber is its use as light fill in Civil engineering and highway projects. This
approach is hampered by the absence of data (5)
.
The shape of a tire allows for easy entrance and containment of
rainwater. This creates an ideal breeding habitat for mosquitoes (6)
In addition to
the nuisance caused by clouds of mosquitoes generated by scrap tire piles,
mosquitoes can carry serious diseases.
Fires emit clouds of noxious black smoke, carbon black, volatile organics, semi-
volatile organics, polynuclear aromatic hydrocarbons, oil, sulfur oxides,
nitrogen oxides, carbon oxides, and airborne particulates, such as arsenic,
cadmium, chromium, lead, zinc, iron, lead, etc, which pose serious
environmental problems to air, water and soil(7)
. So waste tiers presents a very
serious economic and environmental problem we have to re use them to help in
decreasing their hazards economically and environmentally.
Introduction & literature survey Chapter 1
3
Polymeric composites are materials made up of two or more components
and consisting of two or more phases (8)
. These composites have recently drawn
considerable attention, due to the ease with which polymer properties can be
modified to achieve characteristics that can not be achieved by a single polymer
system. The most difficult task is the development of materials with a full set of
desired properties (9)
.
1.2. Thermal properties of polymeric materials
Heat transfer is a discipline of thermal engineering that concerns the
exchange of thermal energy from one physical system to another. Heat transfer
is classified into various mechanisms, such as heat conduction, convection,
thermal radiation, and phase-change transfer. All forms of heat transfer may
occur in some systems (for example, in transparent fluids like the Earth's
atmosphere) at the same time. Heat transfer only occurs because of a
temperature-difference driving force and heat flows from the high to the low
temperature region.(10)
The fundamental modes of heat transfer are:
Conduction or diffusion:
The transfer of energy between objects that are in physical contact .
Convection:
The transfer of energy between an object and its environment, due to
circular fluid motion.
Radiation:
The transfer of energy to or from a body by means of the emission or
absorption of electromagnetic radiation.
Introduction & literature survey Chapter 1
4
Mass transfer:
The transfer of energy from one location to another as a side effect of
physically moving an object containing that energy.
1.2.1Thermal Conductivity
Heat transfer by conduction involves transfer of energy within a material
without any motion of the material as a whole. The rate of heat transfer depends
upon the temperature gradient and the thermal conductivity of the material.
Thermal conductivity is a reasonably straightforward concept when you are
discussing heat loss through the walls of your house, and you can find tables
which characterize the building materials and allow you to make reasonable
calculations.
Conceptually, the thermal conductivity can be thought of as the container for the
medium-dependent properties which relate the rate of heat loss per unit area to
the rate of change of temperature.
𝛥𝑄
𝛥𝑡= −𝑘𝐴
𝛥𝑇
𝛥𝑥 (1.1)
Where;
𝛥Q/Δt is the rate of heat transfear,
ΔT/Δx is the temperature gradient,
A is the cross sectional area, and
k is thermal conductivity coefficient.
In physics, thermal conductivity, k, is the property of a material's ability
to conduct heat. It appears primarily in Fourier's Law for heat conduction.
Thermal conductivity is measured in watts per kelvin-meter (W·K−1·m−1, i.e.
W/(K·m) Multiplied by a temperature difference (in kelvins, K) and an area (in
square meters, m2), and divided by a thickness (in meters, m), the thermal
Introduction & literature survey Chapter 1
5
conductivity predicts the rate of energy loss (in watts, W) through a piece of
material. (11, 12, 13)
The reciprocal of thermal conductivity is thermal resistivity
1.2.1.1Some related Definitions
a. Thermal Conductance
For general scientific use, thermal conductance is the quantity of heat
that passes in unit time through a plate of particular area and thickness when its
opposite faces differ in temperature by one kelvin. For a plate of thermal
conductivity k, area A and thickness L this is kA/L, measured in W·K−1
(equivalent to: W/°C). Thermal conductivity and conductance are analogous to
electrical conductivity (A·m−1
·V−1
) and electrical conductance (A·V−1
).
There is also a measure known as heat transfer coefficient: the quantity of heat
that passes in unit time through unit area of a plate of particular thickness when
its opposite faces differ in temperature by one Kelvin. The reciprocal is thermal
insulance. In summary:
thermal conductance = kA/L, measured in W·K−1
o thermal resistance = L/(kA), measured in K·W−1
(equivalent to:
°C/W)
heat transfer coefficient = k/L, measured in W·K−1
·m−2
o thermal insulance = L/k, measured in K·m²·W−1
.
The heat transfer coefficient is also known as thermal admittance.
Introduction & literature survey Chapter 1
6
b. Thermal Resistance
When thermal resistances occur in series, they are additive. So when heat
flows through two components each with a resistance of 1 °C/W, the total
resistance is 2 °C/W.
A common engineering design problem involves the selection of an appropriate
sized heat sink for a given heat source. Working in units of thermal resistance
greatly simplifies the design calculation. The following formula can be used to
estimate the performance:
c. Thermal Transmittance
A third term, thermal transmittance, incorporates the thermal
conductance of a structure along with heat transfer due to convection and
radiation. It is measured in the same units as thermal conductance and is
sometimes known as the composite thermal conductance. (14)
1.2.1.2 Theoretical consideration for thermal conductivity
measurement
There are a number of ways to measure thermal conductivity. Each of these
is suitable for a limited range of materials, depending on the thermal properties
and the medium temperature.
Introduction & literature survey Chapter 1
7
a. STEADY-STATE METHOD
Determination of the thermal conductance of a sample is a solid-state
transport property measurement in which a temperature difference (ΔT) across a
sample is measured in response to an applied amount of heating power. This is
essentially a measure of the heat flow through the sample. The thermal
conductivity (k) is given by the slope of a power versus (ΔT) sweep at a fixed
base temperature with the dimensions of the specific sample taken into
account(15)
.
𝑘 =𝑄𝐿
𝐴𝛥𝑇 (1.2)
Where k: is total thermal conductivity.
Q: is the quantity of heat flowing through the sample.
A: is the cross sectional area through which power flows
ΔT: is the temperature difference measured.
b. THE COMPARATIVE TECHNIQUE
In the comparative technique a known standard is put in series between the
heater and the sample. This technique, also a steady-state heat flow technique,
achieves the best results when the thermal conductivity of the standard is
comparable to that of the sample.
Introduction & literature survey Chapter 1
8
c .THE RADIAL FLOW METHOD
In the radial heat flow method, heat is applied internally to the sample,
generally minimizing radiative losses from the heat source. As presented by
Tye, (16)
radial flow methods have been applied to solids having a wide range of
thermal conductivities.
d. LASER-FLASH DIFFUSIVITY
Another technique for measuring the thermal properties of thin-film and
bulk samples is the laser-flash thermal diffusivity method. (17)
In this technique
one face of a sample is irradiated by a short (≤1 ms) laser pulse. An IR detector
monitors the temperature rise of the opposite side of the sample. The thermal
diffusivity is calculated from the temperature rise versus time profile.
Algorithms exist for correcting various losses typically present in this
measurement. The thermal conductivity is related to the thermal diffusivity, D =
k/ρd Cp, where ρd is the density, and Cp is the heat capacity.
e. Transient methods (KD2PRO Theory)
The transient techniques perform a measurement during the process of
heating up. The advantage is that measurements can be made relatively quickly.
Transient methods are usually carried out by needle probes.
Non-steady-state methods to measure the thermal conductivity do not require
the signal to obtain a constant value. Instead, the signal is studied as a function
of time. The advantage of these methods is that they can in general be performed
more quickly, since there is no need to wait for a steady-state situation. The
disadvantage is that the mathematical analysis of the data is in general more
difficult.
Introduction & literature survey Chapter 1
9
Carlaw and Jaeger
(18), modeled the temperature surrounding an infinite line heat
source with constant heat output and zero mass, in an infinite medium. When a
quantity of heat Q (J/m) is instantaneously applied to the line heat source, the
temperature rise at distance, r(m)from the source is
𝛥𝑇 = (𝑄/4𝛱𝑘𝑡)𝑒(−𝑟2/4𝐷𝑡) (1.3)
Where k: is the thermal conductivity (W/mK),
D: is the thermal diffusivity (m2/s) and,
t: is time (s).
if a constant amount of heat is applied to a zero mass heater over a period of
time, rather than as an instantaneous pulse, the temperature response is
𝛥𝑇 = 𝑞
4𝛱𝑘𝑡 𝐸𝑖(−
𝑟2
4𝐷𝑡) 0 < t ≤t1 (1.4)
Where q: is the rate of heat dissipation (W/m),
t 1 : is the heating time,
Ei: is the exponential integral (19)
.
The temperature rise after the heat is turned off is given by
𝛥𝑇 = 𝑞
4𝛱𝑘𝑡 (𝐸𝑖 −
𝑟2
4𝐷𝑡 + 𝐸𝑖 −
𝑟2
4𝐷(𝑡−t1) t > t1 (1.5)
Material thermal properties are determined by fitting the time series temperature
data during heating to eq. (1.4), and during cooling to eq. (1.5). Thermal
conductivity can be obtained from the temperature of the heated needle (single
needle), with r taken as the radius of the needle. Diffusivity is best obtained by
fitting the temperature measured a fixed distance from the heated needle (k is
also determined from this data). Volumetric specific heat (W/m3K) is
determined from K& D
Introduction & literature survey Chapter 1
10
𝐶 = 𝑘/𝐷 (1.6)
In each case, k & D are obtained by anon linear least squares procedure (20)
which searches for values of k and D which minimize the difference between
modeled and measured sensor temperatures. An additional linear drift factor is
included in the inverse procedure.
The theory introduced above is based on heat flow from an infinite line heat
source. For the analytical solution just given to accurately describe the physical
behavior of a system, the heat source must closely approximate an infinitely
long, thin line. Kluitenberg et al (21)
give solutions for pulsed cylindrical sources
that are not ideal line heat sources.
1.2.2Heat capacity
Heat capacity (usually denoted by a capital C, often with subscripts), or
thermal capacity, is the measurable physical quantity that characterizes the
amount of heat required to change a body's temperature by a given amount. In
the International System of Units (SI), heat capacity is expressed in units of
joules per kelvin.
𝐶 = 𝑄/∆𝑇 (1.7)
Derived quantities that specify heat capacity as an intensive property,
independent of the size of a sample, are the molar heat capacity, which is the
heat capacity per mole of a pure substance, and the specific heat capacity, often
simply called specific heat, which is the heat capacity per unit mass of a
material.
For many experimental and theoretical purposes it is more convenient to report
heat capacity as an intensive property, as an intrinsically characteristic property
Introduction & literature survey Chapter 1
11
of a particular substance. This is most often accomplished by the specification of
the property per a unit of mass. In science and engineering, such properties are
often prefixed with the term specific.(22)
International standards now recommend
that specific heat capacity always refer to division by mass.(23)
The units for the
specific heat capacity are
𝐶 = 𝐽/𝐾𝑔.𝐾 (1.8)
1.2.3Density
Is a physical property of matter, as each element and compound has a
unique density associated with it. Density defined in a qualitative manner as the
measure of the relative "heaviness" of objects with a constant volume.
Mathematical Definition of Density
The formal definition of density is mass per unit volume. Usually the
density is expressed in grams per mL or cc. (cc is a cubic centimeter) and is
equal to a mL Therefore, (24)
𝜌 =𝑚
𝑣 (1.9)
Where ρ: is density in Kg/m3
m: is mass in Kg
V: is volume in m3
Relative Density (Specific Gravity)
Introduction & literature survey Chapter 1
12
Relative density of a substance is the ratio of the substance to the density of
water at 4oC.
1.2.4Specific Weight
Specific Weight is defined as weight per unit volume. Weight is a force.
y= ρ g (1.10)
Where
y : specific weight (N/m3)
ρ :density (kg/m3)
g : acceleration of gravity (m/s2)
1.3 literature survey for thermal properties
Saxena et al (25)
studied Thermal conductivity of styrene butadiene rubber
compounds with natural rubber prophylactics waste as filler
Efforts on a large
scale have been made by the polymer industry to develop cost effective
techniques to convert waste and used rubber into processable forms. Some of the
authors have developed a cost effective technique for the reuse of natural rubber
(NR) latex condom waste as potential filler in styrene butadine rubber (SBR). It
has been proved that waste NR particles do reinforce SBR matrix. For
optimizing cryo system performance of the blends, characterization of the
composites in terms of thermal behavior is important. Thermal conductivity of
SBR filled with lightly cross-linked NR latex waste is measured using the
transient plane source (TPS) method in the temperature range of 100±300 K. It
has been found that the thermal conductivity of SBR composites increases
Introduction & literature survey Chapter 1
13
linearly with temperature to a peak value at a temperature which lies well within
the glass transition region of SBR. With further increase of temperature the
thermal conductivity decreases asymptotically to a constant value near 300 K. It
has been found that the thermal conductiveness of the SBR composites falls to a
minimum at 10 phr of NR particle content and further addition of NR particles
results in compensating this fall in thermal conductivity due to the decrease in
cross linking density of the composites with increasing filler content.
Leong et al (26) studied Mechanical and thermal properties of talc and
calcium carbonate filled polypropylene hybrid composites they compare the
mechanical and thermal properties of hybrid polypropylene (PP) composites
and single-filler PP composites. With two main types of mineral fillers—
calcium carbonate (CaCO3) and talc—PP composites of different filler weight
ratios (talc/CaCO3) were compounded with a twin-screw extruder and then
injection-molded into dumbbell specimens with an injection-molding machine.
Tensile, flexural, and impact tests were performed to determine and compare
the mechanical properties of the hybrid and single-filler PP composites. A
synergistic hybridization effect was successfully achieved; the flexural strength
and impact strength were highest among the hybrids when the PP/talc/CaCO3
weight ratio was 70:15:15. The nucleating ability of the fillers and its effects on
the mechanical properties were also studied with differential scanning
calorimetry. Because of the influence of talc as the main nucleating agent, the
hybrid fillers showed significant improvements in terms of the nucleating
ability, and this contributed to the increase in or retention of the mechanical
properties of the hybrid composites.
Goyanes et al(27)
studied Thermal properties in cured natural
rubber/styrene butadiene rubber blends Blends of natural rubber (NR) and
Introduction & literature survey Chapter 1
14
styrene butadiene rubber (SBR) were prepared with sulfur and n-t-butyl-2-
benzothiazolesulfonamide (TBBS) as accelerator, varying the amount of each
polymer in the blend. Samples were analyzed by rheometer curing at 433 K until
their maximum torque was reached. The miscibility among the constituent
polymers of the cured compounds was studied in a broad range of temperatures
by means of differential scanning calorimetry, analyzing the glass transition
temperatures of the samples. The specific heat capacity of the compounds was
also determined. Thermal diffusivity of the samples was measured in the
temperature range from 130 to 400 K with a new device that performs
measurements in vacuum. In NR/SBR blends prepared with TBBS(accelerator)/
sulfur and vulcanized at 433 K, there is not aunique glass transition temperature
measured with DSC. Two glass transitions are obtained, each one corresponding
to each phase of the blend. These temperatures are not the same in all the blends.
The thermal diffusivity was measured in the NR/ SBR cured blends and its
variation with temperature shows clearly the transition zone. However, it was
not possible to distinguish the Tg of each phase.. A serial thermal conduction,
model considering the weight fraction of each elastomer and their thermal
diffusivity, can be used to explain the thermal diffusivity of the blend in the
transition and glassy zones.
Yesilata et al (28)
studied Thermal insulation enhancement in concretes by
adding waste PET and rubber pieces they investigated experimentally the
relative change in insulation property of the ordinary concrete due to adding
polymeric based waste material. The polyethylene (PET) bottle and automobile
tire pieces, which can easily be obtained from the environment with almost no
cost, are shredded and added into ordinary concrete to examine heat insulation
behaviors of specimens. Five different concrete samples (one ordinary concrete,
one concrete with scrap rubber pieces and three concretes with waste PET bottle
Introduction & literature survey Chapter 1
15
pieces of various geometries) are considered. The adiabatic hot-box technique is
used for comparing
effective thermal transmittances of these concrete samples. The results reveal
that proper addition of selected waste materials into concrete can significantly
reduce heat loss or improve thermal insulation performance. The degree of
improvement in thermal insulation is found to vary with the added waste
material and geometry of shredded-pieces.
Wooster et al (29)
studied Thermal, mechanical, and conductivity
properties of cyanate ester composites ,Cyanate ester resins have been widely
proposed as replacements for epoxy resins in high temperature applications. One
such application, semiconductor encapsulation, uses a large amount of inorganic
filler, typically 65 wt%. The effect of filler incorporation, on the properties of
cyanate ester composites, was assessed incrementally in this work. It was found
that, as is the case with epoxy based encapsulants, silica filler increased cyanate
ester composite thermal conductivity, Young’s modulus, and dielectric constant
(slightly), and decreased encapsulant thermal expansion. It was also found that
silica addition resulted in a marginal decrease in strength. This indicated a high
degree of interfacial adhesion between the untreated silica filler and the cyanate
ester matrix.
Agari et al(30)
studied Thermal conductivity of polymer filled with
carbon materials they measured Effect of conductive particle chains on thermal
conductivity Thermal and electric conductivities of polyethylene and poly(vinyl
chloride) filled with carbon materials over a wide range in order to study the
effect of formed conductive particle chains on thermal conductivities of the
composites. With increase of content of carbon particles, the amount of formed
conductive chains exponentially increases and the conductive chains tend
largely to increase thermal conductivity of a composite. Some models proposed
Introduction & literature survey Chapter 1
16
to predict thermal conductivity of a composite in a two-phase system could not
be applied to the system with high volume content of particles. In this study, a
new thermal conduction model is proposed to correctly predict thermal
conductivity of a composite which contains various amounts of particles ranging
from a small content, to the region in which conductive chains largely effect a
thermal conductivity of a composite. Thermal conductivity of a polymer filled
with high volume content of particles largely decreased with a rise in
temperature. This phenomenon can be referred to as a PTC phenomenon in
thermal resistance.
Sarkhel et al (31)
deals with the mechanical, thermal and viscoelastic
properties of ternary composites based on low density polyethylene (LDPE)-
ethylene-propylene-diene terpolymer (EPDM) blend and high density
polyethylene (HDPE)-EPDM blend reinforced with short jute fibers. For all the
untreated and compatibilizer treated composites, the variation of mechanical and
viscoelastic properties as a function of fiber loading (10, 20 and 30 wt %) and
compatibilizer concentration (1, 2, and 3%) were evaluated. The flexural
strength, flexural modulus, impact strength, and hardness increased with
increasing both the fiber loading and the compatibilizer dose. The storage
modulus (E ) and loss modulus (E ) of the HDPE-EPDM/jute fiber composites
were recorded higher compared to those of the LDPE-EPDM/jute fiber
composites at all level of fiber loading and compatibilizer doses. The tan
(damping efficiency) spectra showed a strong influence of the fiber loading and
compatibilizer dose on the relaxation process of polymer matrix in the
composite. The thermo-oxidative stability was significantly enhanced for treated
composites compared to untreated composites. Scanning electron microscopy
investigation confirmed that the higher values of mechanical and viscoelastic
Introduction & literature survey Chapter 1
17
properties of the treated composites compared to untreated composites is caused
by improvement of fiber-matrix adhesion as result of compatibilizer treatment.
Eiermann, et al (32)
made a Systematic measurements of the thermal
conductivity of plastics by various methods and checked against each other.
Between −180 and +100°C. The thermal conductivity depends only slightly on
the temperature. For instance, amorphous plastics and natural rubber show a
break in the curve at the second-order transition temperature. This break
probably is connected with the break in the volume versus temperature curve. In
stretched samples, the thermal conductivity was found to be larger when
stretching was in a direction parallel than perpendicular to the chains. Partially
crystalline plastics show a more complex behavior.
Najidha, et al (33)
they investigated the thermal transport properties of
Natural Rubber/Polyaniline and Natural Rubber/Polyaniline/Carbon black
composites by Transient Plane Source (TPS) Technique at room temperature.
The samples of different weight percentage (typically 20,30,40,50 and 60%) of
fillers have been taken. The composites were prepared by dry mill mixing in a
roll-mill and vulcanized in a hot press. It has been found that the effective
thermal conductivity and effective thermal diffusivity of the both the composites
increase as the fraction of filler increases.