Polypropylene is a plastic polymer with the chemical formula C3H6. It is used
in many different settings, both in industry and in consumer goods, and it can be
used both as a structural plastic and as a fiber. This plastic is often used for food
containers, particularly those that need to be dishwasher safe.
The melting point of polypropylene is very high compared to many other plastics, at
320°F (160°C), which means that the hot water used when washing dishes will not
cause dishware made from this plastic to warp. This contrasts with polyethylene,
another popular plastic for containers, which has a much lower melting point.
Polypropylene is also very easy to add dyes to, and it is often used as a fiber in
carpeting that needs to be rugged and durable, such as that for use around
swimming pools or on miniature golf courses. Unlike nylon, which is also often used
as a fiber for rugged carpeting, it doesn't soak up water, making it ideal for uses
where it will be constantly subject to moisture.
Research is ongoing with polypropylene, as makers experiment with different
methods for synthesizing it. Some of these experiments yield the promise of exciting
new types of plastic, with new consistencies and a different feel from the fairly rigid
version that most people are used to. These new elastic versions are very rubbery,
making them even more resistant to shattering and opening up many different uses
for an already pervasive plastic.
Polypropylene is not as sturdy as polyethylene, but it has benefits that make it the
better choice in some situations. One of these situations is creating hinges from a
plastic, such as a plastic lid on a travel mug. Over time, plastics wear out from the
repetitive stress of being opened and shut, and eventually will break. Polypropylene
is very resistant to this sort of stress, and it is the plastic most often used for lids and
caps that require a hinging mechanism.
Like many plastics, polypropylene has virtually endless uses, and its development
has not slowed since its discovery. Whether used for industrial molds, rugged
currency, car parts, orstorage containers, it is one of a handful of materials the world
is literally built around.
Polypropylene pipe is used in many industrial settings due to its chemical and
thermal resistance, affordability, and cost. It is frequently used in waste streams of all
types, including residential and commercial environments. A byproduct of the
distillation of petroleum products, polypropylene was discovered in the early 1950s
and due to its relatively easy manufacture was in production within seven years. New
uses have often been developed for this recyclable, resilient material.
This material is a straight-chain thermoplastic consisting of methyl groups on every
other carbon with an empirical formula of C3H6. Polypropylene used for pipe is
primarily isotatic, wherein the methyl groups are all in the same position on the
carbon backbone, resulting in a medium molecular weight and a degree of
crystallinity between that of low-density polyethylene (LDPE) and high-density
polyethylene (HDPE). These properties produce a pipe that is resistant to acids,
bases, and solvents and which is excellent in transporting industrial streams
between processes. The material is tinted black or gray to decrease ultraviolet (UV)
light degradation of the pipe and its contents.
Strongly caustic streams, including potassium hydroxide or sodium hydroxide
solutions, may be carried in polypropylene pipes. By the use of fusion-weld joints,
caustic attack on solvent-based adhesives is avoided. A glass additive is required to
make polypropylene capable of handling biodiesel (methyl oleate) fuels. This type of
pipe is not used with concentrated, strong oxidizing agents such as nitric acid.
In addition to harsh environments, polypropylene pipe is employed in the transport of
distilled water in all but the most stringent requirements. The pipe’s lack of reactivity
and the ability to fusion-weld joints without adhesives maintains the water’s purity.
The pipe may be used in pressurized applications to 150°F (65°C) and to 180°F (
82°C) in non-pressurized uses. Without modification, the pipe’s use is limited to 20
psi (138 kPa). Other liquid applications include service in the heating and cooling of
buildings, providing an economical alternative to the use of air as the heat transport
medium.
Polypropylene is manufactured from low molecular weight natural gas components
or petroleum distillation byproducts using chromium catalysts at low pressures, a
lower-cost process than HDPE. As polypropylene pipe is less dense than other
thermoplastics and certainly much less dense than steel, iron, or copper pipes,
transportation costs are lower. Piping made from polypropylene is recyclable and
has a lifetime of about 50 years.
The pipe does not conduct electricity, another advantage over metal pipes in
industrial settings. Homeowners sometimes feel polypropylene piping in residential
waste systems is noisy, as sound easily penetrates the pipe walls, and a long stretch
of open pipe can act as a drum. Polypropylene pipe itself is very tough and not
subject to splitting. Go-kart racetracks and similar venues often employ
polypropylene pipe as low-cost barrier or guard rails due to its ability to withstand
stress and temperature extremes.
Polypropylene (PP) - This polyolefin is readily formed by polymerizing propylene with
suitable catalysts, generally aluminum alkyl and titanium tetrachloride. Polypropylene
properties vary according to molecular weight, method of production, and the
copolymers involved. Generally polypropylene has demonstrated certain advantages
in improved strength, stiffness and higher temperature capability over polyethylene.
Polypropylene has been very successfully applied to the forming of fibers due to its
good specific strength which is why it is the single largest use of polypropylene.
Polypropylene also happens to be one of the lightest plastics available with a density
of 0.905 g/cm².
Polypropylene (PP) was discovered in 1954 and grew a strong popularity very
quickly. Because of extensive research, five main variations of Polypropylene have
emerged as: homopolymers, impact (block) copolymers, random copolymers, rubber
modified blends, and specialty copolymers.
Features
Homopolymer (3217), Food Contact Acceptable (1773), Good Processability (1638),
Copolymer (1365), Good Impact Resistance (1359), High Flow (1328), Good
Stiffness (1296), High Impact Resistance (1188), High Stiffness (1143), Chemically
Coupled (1080), 284 More...
Uses
Automotive Applications (2165), Household Goods (1132), Containers (763), Film
(701), Appliances (689), Electrical/Electronic Applications (641), Packaging (639),
General Purpose (571), Automotive Interior Parts (567), Industrial Applications (539),
262 More...
Disadvantages
- Degraded by UV
- Flammable, but retarded grades available
- Attacked by chlorinated solvents and aromatics
- Difficult to bond
- Several metals accelerate oxidative degrading
- Low temperature impact strength is poor
Typical Properties and Processing Information
Polyethylene (PE) - The term polyethylene describes a huge family of resins
obtained by polymerizing ethylene gas, H2C=CH2, and it is by far the largest volume
commercial polymer. This thermoplastic is available in a range of flexibilities and
other properties depending on the production process, with high density materials
being the most rigid. Polyethylene can be formed by a wide variety of thermoplastic
processing methods and is particularly useful where moisture resistance and low
cost are required. Low density polyethylene typically has a density value ranging
from 0.91 to 0.925 g/cm³, linear low density polyethylene is in the range of 0.918 to
0.94 g/cm³, while high density polyethylene ranges from 0.935 to 0.96 g/cm³ and
above.
After its experimental preparation in the 1930s the application in high frequency
radar cables during World War II gave impetus to its commercial production. Today
Polyethylene (PE) is one of the most widely used plastics with production in the
billions of pounds each year.
Features
Food Contact Acceptable (1924), Good Processability (1775), Antioxidant (1115),
High ESCR (Stress Crack Resist.) (1022), Copolymer (975), Good Impact
Resistance (643), Good Toughness (634), Good Stiffness (571), Low Density (554),
High Impact Resistance (513), 259 More...
Uses
Film (2179), Packaging (1078), Bags (691), Piping (588), Industrial Applications
(552), Containers (517), Food Packaging (459), Laminates (433), Wire & Cable
Applications (425), Liners (424), 285 More...
Disadvantages
- High thermal expansion
- Poor weathering resistance
- Subject to stress cracking
- Difficult to bond
- Flammable
- Poor temperature capability
- Low strength/stiffness
Polyethylene is a type of polymer that is thermoplastic, meaning that it can be melted
to a liquid and remolded as it returns to a solid state. It is chemically synthesized
from ethylene, a compound that's usually made from petroleum or natural gas. Other
non-official names for this compound include polythene or polyethylyne; and it is also
abbreviated as PE. It is used in making other plastic compounds much often than it's
used in its pure form. Though it has a wide variety of uses, it can be harmful to
humans and to the environment.
Production and Uses
Of all the plastics produced for industrial and commercial products, polyethylene is
the most common. As an example, 280 million metric tonnes of it was produced in
2011 alone. Over five times as much PE is manufactured each year than a closelyrelated compound,polypropylene (PP). The largest use for these polymers is in
packaging materials, like films and foam; and for bottles and other containers that
can be used in food, medical, and other consumer industries.
The characteristics of a plastic can be adjusted by combining it with various
plasticizers, which are substances added to plastics to make them more durable,
flexible, and transparent. Adding chromium/silica makes high-density polyethylene
(HDPE), which is used to create sturdy products like garbage containers. Combining
it with organic olefin compounds makes a type of low-density PE (LDPE) that is used
for plastic grocery or shopping bags. Other common forms of polyethylene are ultra
high molecular weight PE (UHMWPE), which is used in bullet-proof vests and knee
joint replacements; and medium-density PE (MDPE), which is crack resistant for
applications in gas pipe pressure fittings.
Plastics based on the PE molecule are widespread because the compound has
physical characteristics that are considered safe and useful in a range of
environments. These traits include the fact that it remains pliable for an extended
period of time while remaining inert and impervious to damage by most liquids. Since
its softness and strength level can be easily adjusted and it can be dyed many
colors, it is often used in consumer products from food wrap to shampoo bottles, milk
containers, toys, and grocery bags.
Potential Dangers
Depending on the compounds its bonded with, PE's level of toxicity and flammability
varies considerably. There are concerns about two versions of the compound in
particular, both of which are often used for medical and consumer purposes.
Polyethylene-glycol (PEG), which acts as a binding agent for many drugs and is also
found in products like shampoo and toothpaste, can cause allergic reactions in
certain individuals. Some people experience nausea, flatulence, and diarrhea after
being exposed to it, while others get a hives-like rash. The elderly seem to be
particularly prone to these side effects.
In addition, harmful chemicals — including the plasticizer phthalate — may leach
from polyethylene-terephthalate (PET), which has been widely used in the plastic
bottling industry. Phthalate is associated with hormonal imbalances, increases in
allergies, and reduced fertility. Some studies show that it may also contribute to the
development of obesity and breast cancer.
Environmental Impact
While PE may help to make many useful and durable products possible, its
environmental impact concerns many experts. It doesn't biodegrade easily, and can
sit in a landfill for hundreds of years. About 20%-24% of all landfill space in the US
alone is taken up by plastics, including polyethylene products. However, recycling
may reduce this problem, since PE scrap can be melted down and reused.
Additionally, an aerobic bacteria called Sphingomonas can significantly reduce the
amount of time it takes some forms of PE to break down, though it is not yet widely
used. Environmental preservation efforts have also led to the development of
bioplastics, with the aim of creating polyethylene from ethanol made from sugarcane.
Polyoxymethylene (POM), also known as acetal,[1] polyacetal and
polyformaldehyde, is an engineering thermoplastic used in precision parts requiring
high stiffness, low friction and excellent dimensional stability. As with many other
synthetic polymers, it is produced by different chemical firms with slightly different
formulas and sold variously by such names as Delrin, Celcon, Duracon and
Hostaform.
Typical applications for injection-molded POM include high performance engineering
components such as small gear wheels, ball bearings, ski bindings, fasteners, knife
handles, lock systems, and model rocket launch buttons. The material is widely used
in the automotive and consumer electronics industry. The M-16 rifle's stock and other
parts are made of it. POM is characterized by its high strength, hardness and rigidity
to −40 °C. POM is intrinsically opaque white, due to its high crystalline composition,
but it is available in all colors. POM has a density of ρ = 1.410–1.420 g/cm³.[5]
POM homopolymer is a semi-crystalline polymer (75–85% crystalline) with a melting
point of 175 °C. The POM copolymer has a slightly lower melting point of 162–173
°C.
POM is a tough material with a very low coefficient of friction. However, it is
susceptible to polymer degradation catalyzed by acids, which is why both polymer
types are stabilized. Both homopolymer and copolymer have chain end groups
(introduced via end capping) which resist depolymerization. With the copolymer, the
second unit normally is a C2 (ethylene glycol) or C4 (1,4-butanediol) unit, which is
introduced via its cyclic acetal (which can be made from the diol and formaldehyde)
or cyclic ether (e.g. ethylene oxide). These units resist chain cleavage, because the
O-linkage is now no longer an acetal group, but an ether linkage, which is stable to
hydrolysis. POM is sensitive to oxidation, and an anti-oxidant is normally added to
molding grades of the material.
POM advantages:
•
High abrasion resistance
•
Low coefficient of friction
•
High heat resistance
•
Good electrical and dielectric properties
•
Low water absorption
•
Acetal resins are sensitive to acid hydrolysis and oxidation by agents such as
mineral acids and chlorine. POM homopolymer is also susceptible to alkaline attack
and is more susceptible to degradation in hot water. Both POM homopolymer and
copolymer are stabilized to mitigate these types of degradation. Thus low levels of
chlorine in potable water supplies (1–3 ppm) can be sufficient to cause stress
corrosion cracking to develop, a problem which has been experienced in both the
USA and Europe in domestic and commercial water supply systems. Defective
mouldings are most sensitive to cracking, but normal mouldings will succumb if the
water is hot.
•
Widespread failure of acetal mouldings in potable and hot water supplies
resulted in one of the largest class actions in the USA when acetal plumbingfittings
cracked and caused flooding of homes, a problem exacerbated by similar problems
with polybutylene pipework. The acetal fittings tended to fail first, followed by the
pipework.[citation needed]
•
In chemistry applications, whilst the polymer is often suitable for the majority
of glassware work, it can succumb to catastrophic failure. An example of this would
be using the polymer clips on hot areas of the glassware (such as a flask to column,
column to head or head to condenser joint during distillation). As the polymer is
sensitive to both chlorine and acid hydrolysis, it may perform very poorly when
exposed to the reactive gases, particularly hydrogen chloride. Failures in this latter
instance can occur with seemingly unimportant exposures from well sealed joints,
and do so without warning and rapidly (the component will split or fall apart). This
can be a significant health hazard as the glass may open or smash. Here, PTFE or a
high grade stainless steel may be a more appropriate choice.
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Polysulfone describes a family of thermoplastic polymers. These polymers are
known for their toughness and stability at high temperatures. They contain the
subunit aryl-SO2-aryl, the defining feature of which is the sulfone group.
Polysulfones were introduced in 1965 by Union Carbide. Due to the high cost of raw
materials and processing, polysulfones are used in specialty applications and often
are a superior replacement for polycarbonates.
These polymers are rigid, high-strength, and transparent, retaining these properties
between −100 °C and 150 °C. It has very high dimensional stability; the size change
when exposed to boiling water or 150 °C air or steam generally falls below 0.1%. Its
glass transition temperature is 185 °C.
Polysulfone is highly resistant to mineral acids, alkali, and electrolytes, in pH ranging
from 2 to 13. It is resistant to oxidizing agents, therefore it can be cleaned by
bleaches. It is also resistant tosurfactants and hydrocarbon oils. It is not resistant to
low-polar organic solvents (e.g. ketones and chlorinated hydrocarbons), and
aromatic hydrocarbons. Mechanically, polysulfone has high compaction resistance,
recommending its use under high pressures. It is also stable in aqueous acids and
bases and many non-polar solvents; however it is soluble in dichloromethane
andmethylpyrrolidone.[1]
Polyethersulfone (PES) is a similar polymer with low protein retention.
Polysulfone has one of the highest service temperature of all melt-processable
thermoplastics. Its resistance to high temperatures gives it a role of a flame
retardant, without compromising its strength that usually results from addition of
flame retardants. Its high hydrolysis stability allows its use in medical applications
requiring autoclave and steam sterilization. However, it has low resistance to some
solvents and undergoes weathering; this weathering instability can be offset by
adding other materials into the polymer.
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Polysulfone (PSU) - Manufacturers - Materials - Classification
Polysulfone (PSU) - A family of sulfur-containing thermoplastics, closely related to
polyethersulfone (PES). The structure of the polysulfones is aromatic groups,
generally with more than one benzene ring, joined by a sulfone group. Generally,
polysulfone is a high cost, rigid, amorphous material with low moisture absorption.
Reinforcement improves toughness and further enhances dimensional stability, but
turns materials opaque. In addition, polysulfones are characterized by high strength,
very high surface-temperature limits, low creep, good electrical characteristics,
transparency, self-extinguishing ability, and resistance to greases, many solvents,
and chemicals. Polysufones may be processed by extrusion, injection molding, and
blow molding.
Polysulfone (PSU), introduced by Union Carbide in 1965, was among the first
thermoplastics developed for long term service beyond 300°F.
Features
Flame Retardant (93), Good Chemical Resistance (92), High Heat Resistance (88),
Lubricated (85), Good Dimensional Stability (76), Good Toughness (62), Hydrolysis
Resistant (50), Acid Resistant (49), Good Creep Resistance (45), Good Thermal
Stability (41), 102 More... Uses
Medical/Healthcare Applications (59), Electrical/Electronic Applications (51),
Aerospace Applications (50), Food Service Applications (29), Engineering Parts (26),
Automotive Applications (26), Electrical Parts (23), Automotive Electronics (20),
Appliances (19), Sporting Goods (19), 64 More...
Disadvantages
- Attacked by some solvents
- Poor weatherability
- Subject to stress cracking
- Processing difficulties
- Increased costs
PVC is replacing traditional building materials such as wood, metal, concrete and
clay in many applications.
Versatility, cost effectiveness and an excellent record of use mean it is the most
important polymer for the construction sector, which accounted for 60 per cent of
European PVC production in 2006.
Polyvinyl chloride, PVC, is one of the most popular plastics used in building and
construction. It is used in drinking water and waste water pipes, window frames,
flooring and roofing foils, wall coverings, cables and many other applications as it
provides a modern alternative to traditional materials such as wood, metal, rubber
and glass. These products are often lighter , less expensive and offer many
performance advantages.
Strong and lightweight
PVC's abrasion resistance, light weight, good mechanical strength and toughness
are key technical advantages for its use in building and construction applications.
Easy to install
PVC can be cut, shaped, welded and joined easily in a variety of styles. Its light
weight reduces manual handling difficulties.
Durable
PVC is resistant to weathering, chemical rotting, corrosion, shock and abrasion. It is
therefore the preferred choice for many different long-life and outdoor products. In
fact, medium and long-term applications account for some 85 per cent of PVC
production in the building and construction sector.
For example, it is estimated that more than 75 per cent of PVC pipes will have a
lifetime in excess of 40 years with potential in-service lives of up to 100 years. In
other applications such as window profiles and cable insulation, studies indicate that
over 60 per cent of them will also have working lives of over 40 years.
Cost-effective
PVC has been a popular material for construction applications for decades due to its
physical and technical properties which provide excellent cost-performance
advantages. As a material it is very competitive in terms of price, this value is also
enhanced by the properties such as its durability, lifespan and low maintenance.
Safe material
PVC is non-toxic. It is a safe material and a socially valuable resource that has been
used for more than half a century. It is also the world's most researched and
thoroughly tested plastic. It meets all international standards for safety and health for
both the products and applications for which it is used.
The study 'A discussion of some of the scientific issues concerning the use of PVC'
(1) by the Commonwealth Scientific and Industrial Research Organisation (CSIRO)
in Australia concluded in 2000 that PVC in its building and construction applications
has no more effect on the environment that its alternatives.
Substitution of PVC by other materials on environmental grounds with no additional
research or proven technical benefits will also result in higher costs. For example, as
part of a housing renovation project at Bielefeld in Germany , it has been estimated
that the replacement of PVC by other materials would lead to a cost increase of
approximately 2,250 euro for an average sized apartment.
Restrictions on PVC use in construction applications would not only have negative
economic consequences but also have wider social impacts, such as in the
availability of affordable housing.
Fire resistant
Like all other organic materials used in buildings, including other plastics, wood,
textiles etc., PVC products will burn when exposed to a fire. PVC products however
are self-extinguishing, i.e. if the ignition source is withdrawn they will stop burning.
Because of its high chlorine content PVC products have fire safety characteristics,
which are quite favourable as. they are difficult to ignite, heat production is
comparatively low and they tend to char rather than generate flaming droplets.
But if there is a bigger fire in a building, PVC products will burn and will emit toxic
substances like all other organic products.
The most important toxicant emitted during fires is carbon monoxide (CO), which is
responsible for 90 to 95 % of deaths from fires. CO is a sneaky killer, since we
cannot smell it and most people die in fires while sleeping. And of course CO is
emitted by all organic materials, be it wood, textile or plastics.
PVC as well as some other materials also emits acids. These emissions can be
smelled and are irritating, making people try to run away from the fire. A specific
acid, hydrochloric acid (HCL), is connected with burning PVC . To the best of our
knowledge, no fire victim has ever been proven scientifically to have suffered HCl
poisoning.
Some years ago no big fire was discussed without dioxins playing a major role both
in communication and measuring programmes. Today we know that dioxins emitted
in fires do not have an impact on people following the results of several studies on
fire exposed people: The dioxin levels measured were never elevated against
background levels. This very important fact has been recognised by official reports
and we know that many other carcinogens are emitted in all fires, such as polycyclic
aromatic hydrocarbons (PAH) and fine particles, which present a much higher
hazard than dioxins.
So there are very good reasons to use PVC products in buildings, since they perform
well technically, have good environmental and very good economic properties, and
compare well with other materials in terms of fire safety.
Good insulator
PVC does not conduct electricity and is therefore an excellent material to use for
electrical applications such as insulation sheathing for cables.
Versatile
The physical properties of PVC allow designers a high degree of freedom when
designing new products and developing solutions where PVC acts as a replacement
or refurbishment material.
PVC has been the preferred material for scaffolding billboards, interior design
articles, window frames, fresh and waste water systems, cable insulation and many
more applications.
Plastics are also called synthetic resins and are broadly classified into two
categories: thermosetting resins and thermoplastic resins.
The thermosetting resins include phenolic resin and melamine resin, which are
thermally hardened and never become soft again. Thermoplastic resins include PVC,
polyethylene (PE), polystyrene (PS) and polypropylene (PP), which can be resoftened by heating.
Usually, thermoplastics are supplied in the form of pelletised material (compounds)
with additives (antioxidants, etc.) already blended in it. However, PVC resin is often
supplied in powder form and long term storage is possible since the material is
resistant to oxidation and degradation. Various additives and pigments are added to
PVC during the processing stage, and the blend is then converted into PVC
products.
PVC is sometimes known as ‘Vinyl’ in Europe and predominantly so in North
America. In Europe, ‘Vinyl’ usually refers to certain specific flexible applications, such
as flooring, decorative sheets and artificial leather.
PVC is a thermoplastic made of 57% chlorine (derived from industrial grade salt) and
43% carbon (derived predominantly from oil / gas via ethylene). It is less dependent
than other polymers on crude oil or natural gas, which are nonrenewable, and hence
can be regarded as a natural resource saving plastic, in contrast to plastics such as
PE, PP, PET and PS, which are totally dependent on oil or gas. This chlorine gives
to PVC excellent fire resistance.
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