1.1 GENERAL
A brick is building material used to make
walls, pavements and other elements in masonry construction. Traditionally, the term
brick referred to a unit composed of clay, but it is now used to denote any rectangular units laid in
mortar. A brick can be composed of clay-bearing soil, sand and lime, or
concrete materials. Bricks are produced in numerous classes, types, materials,
and sizes which vary with region and time period, and are produced in bulk
quantities. Two basic categories of bricks are fired and non-fired bricks.
BRICKS
Block is a similar term referring to a
rectangular building unit composed of similar materials, but is usually larger
than a brick. Lightweight bricks (also called "lightweight blocks")
are made from expanded
clay aggregate.
Fired bricks are one of the
longest-lasting and strongest building materials, sometimes referred to as artificial
stone, and have been used since circa 5000 BC. Air-dried bricks, also known as mud bricks, have a history older than fired
bricks, and have an additional ingredient of a mechanical binder such as straw.
Bricks
are laid in courses and numerous patterns known as bonds,
collectively known as brickwork,
and may be laid in various kinds of mortar to
hold the bricks together to make a durable structure.
1.2
THE PROPERTIES OF POLYSTYRENE (THERMOCOL):
1.2.1 History
Polystyrene was discovered in 1839 by Eduard Simon, an apothecary from Berlin. From storax, the resin of the Turkish sweet gum tree Liquidambar oriental is, he distilled an oily substance, a monomer that he named
styrol. Several days later, Simon found that the styrol had thickened,
presumably from oxidation, into a jelly he dubbed styrol oxide
("Styroloxyd"). By 1845 Jamaican-born chemist John Buddle Blyth and
German chemist August Wilhelm von
Hofmann showed
that the same transformation of styrol took place in the absence of oxygen.
They called their substance metastyrol. Analysis later showed that it was
chemically identical to Styroloxyd. In 1866 Marcel in Berthelot correctly identified the formation
of Metastyrol / Styroloxyd from styrol as a polymerization process. About 80 years later it was realized that heating
of styrol starts a chain reaction that produces macromolecules, following the thesis of German organic chemist Hermann Staudinger (1881–1965). This eventually led to
the substance receiving its present name, polystyrene.
The company I. G. Farben began manufacturing polystyrene in Ludwigshafen, about 1931, hoping it would be a suitable replacement for
die-cast zinc in many applications. Success was achieved when they
developed a reactor vessel that extruded polystyrene through a heated tube and
cutter, producing polystyrene in pellet form.
In 1941, Dow Chemical invented a Styrofoam process. Before 1949, the chemical
engineer Fritz Stastny (1908–1985) developed pre-expanded PS beads by
incorporating aliphatic hydrocarbons, such as pentane. These beads are the raw
material for moulding parts or extruding sheets. BASF and Stastny applied for a patent
that was issued in 1949. The moulding process was demonstrated at the
Kunststoff Messe 1952 in Düsseldorf. Products were named Styropor.
In
1954, the Koppers Company in Pittsburgh,
Pennsylvania,
developed expanded polystyrene (EPS) foam under the trade name Dylite.
In
1988, the first U.S. ban of general polystyrene foam was enacted in Berkeley,
California.
In 1954, the Koppers Company in Pittsburgh,
Pennsylvania,
developed expanded polystyrene (EPS) foam under the trade name Dylite.
In 1988, the first U.S. ban of general polystyrene foam was
enacted in Berkeley, California.
In 1954, the Koppers Company in Pittsburgh,
Pennsylvania,
developed expanded polystyrene (EPS) foam under the trade name Dylite.
In 1988, the first U.S. ban of general polystyrene foam was
enacted in Berkeley, California.
Names
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Poly(1-phenylethene) Other names
Thermocol
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Identifiers
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Abbreviations
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PS
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Properties
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(C8H8)n
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0.96–1.04 g/cm3
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0.033 W/(m·K) (foam, ρ 0.05 g/cm3)
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Refractive index (nD)
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Related compounds
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Related compounds
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Except where otherwise noted, data
are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
1.2.2 Structure
In chemical terms, polystyrene is a long chain
hydrocarbon wherein alternating carbon centers are attached to phenyl groups (the name given to the aromatic ring benzene).Polystyrene's chemical formulais (C8H8) it contains the chemical elements carbon and hydrogen.
The material's properties are determined by short-range van DerWaals attractions between polymers
chains. Since the molecules are long hydrocarbon chains that consist of
thousands of atoms, the total attractive force between the molecules is large.
When heated (or deformed at a rapid rate, due to a combination of viscoelastic
and thermal insulation properties), the chains are able to take on a higher
degree of conformation and slide past each other. This intermolecular weakness (versus the high intramolecular strength due to the hydrocarbon
backbone) confers flexibility and elasticity. The ability of the system to be
readily deformed above its glass transition temperature allows polystyrene (and
thermoplastic polymers in general) to be readily softened and molded upon
heating.
Extruded polystyrene is about as strong as an unalloyed aluminum, but much more flexible and much lighter (1.05 g/cm3
vs. 2.70 g/cm3 for aluminum).
Polystyrene (PS) a synthetic aromatic polymer made from the monomer styrene. Polystyrene can be solid or foamed. General-purpose
polystyrene is clear, hard, and rather brittle. It is an inexpensive resin per
unit weight. It is a rather poor barrier to oxygen and water vapor and has a
relatively low melting point. Polystyrene is one of the most widely used plastics, the scale of its production being several billion
kilograms per year. Polystyrene can be naturally transparent, but can be colored with colorants.
Uses include protective packaging (such as packing peanuts and CD and DVD cases), containers (such as
"clamshells"), lids, bottles, trays, tumblers, and disposable cutlery.
As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room
temperature but flows if heated above about 100 °C, its glass transition
temperature.
It becomes rigid again when cooled. This temperature behavior is exploited for extrusion (as in Styrofoam) and also for molding and vacuum forming, since it can be cast into molds with fine detail.
Polystyrene is very slow to biodegrade and is therefore a focus of controversy among
environmentalists. It is increasingly abundant as a form of litter in the outdoor environment, particularly along shores and
waterways, especially in its foam form, and also in increasing quantities in
the Pacific Ocean.
Polymerization
Polystyrene results when styrene monomers interconnect. In
the polymerization, the carbon-carbon pi bond (in the vinyl group) is broken and a new
carbon-carbon single (sigma) bond is formed, attaching another styrene monomer
to the chain. The newly formed sigma bond is much stronger than the pi bond
that was broken, thus it is very difficult to depolymerize polystyrene. About a
few thousand monomers typically comprise a chain of polystyrene, giving a molecular
weight of
100,000–400,000.
A 3-D model would show that each of
the chiral backbone carbons lies at the center
of a tetrahedron, with its 4 bonds pointing toward the vertices. Consider that the -C-C- bonds
are rotated so that the backbone chain lies entirely in the plane of the
diagram. From this flat schematic, it is not evident which of the phenyl (benzene) groups are angled outward from the plane of the
diagram, and which ones are inward. The isomer where all of the phenyl groups are on the same side is
called isotactic polystyrene,
which is not produced commercially. Atactic polystyrene
The only commercially important form of polystyrene is atactic, in which the phenyl groups
are randomly distributed on both sides of the polymer chain. This random
positioning prevents the chains from aligning with sufficient regularity to
achieve any crystallinity. The plastic has a glass transition
temperature Tg of
~90 °C. Polymerization is initiated with free radicals.
Syndiotactic
polystyrene
Ziegler-Natta
polymerization
can produce an ordered syndiotactic
polystyrene with the phenyl groups positioned on alternating sides of the
hydrocarbon backbone. This form is highly crystalline with a Tm of 270 °C
(518 °F). Syndiotactic polystyrene resin is currently produced under the
trade name XAREC by Idemitsu corporation. Syndiotactic polystyrene is prepared
by combining a metallocene catalyst with a styrene monomer to generate a
polystyrene chain with a syndiotactic structure.
Degradation
Polystyrene is very chemically inert, being resistant to
acids and bases but is easily dissolved by many chlorinated solvents, and many
aromatic hydrocarbon solvents. Because of its resilience and inertness, it is
used to fabricate many objects of commerce. It is attacked by many organic
solvents, which dissolve the polymer. Foamed polystyrene is used for packaging
chemicals.
Like all organic compounds, polystyrene burns to give carbon dioxide and water vapor. Polystyrene, being an aromatic hydrocarbon, typically combusts incompletely as
indicated by the sooty flame.
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