Plastics - class-XI

Some characters of thermosetting polymers:

Melamine-formaldehyde polymer is cross-linked polymer or thermosetting polymer which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins, etc.

Bakelite, melamine( thermosetting) and vulcanised rubber( elastomer) have cross-linkages in the structures whereas Teflon is linear addition or chain growth polymers that have not cross-linkages.

[A] Elastomers - these are rubber like solids with elastic properties

Teflon is a synthetic polymer (polytetrafluoroethylene) that can be used to cover the surface of certain object and imparts nonstick properties to it. Teflon is used for Non Stick material because the monomer units are hydrophobic in nature (tetrafluoroethylene) and thus oil and water do not stick to it.
option A is correct.

Plastics are categorized into thermosoftening/thermoplastic and thermosetting/thermoset plastics.
In thermosoftening plastics, the forces between the polymer chains are weak, so they can easily be remoulded
into new shapes. This makes it possible to recycle this type of
plastic. whereas in thermosetting plastics there are strong covalent
bonds forming cross-links between the polymer chains, making these
plastics hard and rigid. Once set into its original shape, a
thermosetting plastic can't be softened and remoulded. The strong bonds between polymers also mean that thermosetting plastics are much more heat resistant than thermosoftening ones.
Cooking pans' handle are made from thermosetting plastic like bakelite as this is resistant to heat.
option A is correct

Plastics are high molecular weight (macromolecular or polymeric) organic substances that have usually been synthesized from low molecular weight compounds. Being organic origin have no ionic character in them and thus can not conduct electricity. They are insulators.
Hence, option $B$ is correct.

Plastics find many applications in day-to-day life because of various reasons as :

Plastic waste is one of many types of wastes that take too long to decompose. Normally, plastic items can take up to 1000 years to decompose in landfills. But plastic bags we use in our everyday life take 10-1000 years to decompose, while plastic bottles can take 450 years or more.

Electrical wires are covered in plastic because plastic is an insulator (bad conductor), which prevents electricity from leaking or causing shocks.

Burning of plastic produces carbon dioxide which causes heavy air pollution. 

Plastics are composed of long chains of repeating units called monomers, making them polymers.

Plastics are classified by their molecular structure as either linear (thermoplastics) or cross-linked (thermosetting plastics).

Thermoplastics on heating get deformed (its shape and size can be altered) and thus can also be bent. On the other hand, thermosetting plastics cannot be bent once moulded. Some examples of Thermoplastics are – Polythene and PVC. Some examples of Thermosetting plastics are – Bakelite and Melamine.

A material which is not easily decomposed by natural processes is termed as $\text {non-biodegradable material}$. Examples are polyethene, PVC, PS. It takes many years for decomposition. Hence, option B is correct.

Plastics in health care industry are used in packaging of medicines;plastic threads are used for stitching wounds. Also syringes, gloves and many kind of medical instruments are made up of plastic.

Plastics are used to store food because:
(i) Plastics are light in weight.
(ii) Plastic is a strong and durable material and
(iii) plastics are easy to handle.

 Telephone instruments, plastic toys, ball point pens, plastic bowls  are thermoplastics and so can be recycled.
Cooker handles, carry bags, plastic covering on electric wire, plastic chains etc are thermosetting plastics and so cannot be recycled.

Plastics are used for buckets because they do not react with or dissolve in water, making them durable and waterproof.

Plastic is also a polymer like the synthetic fibre. It is the chain of small units joined together.

A thermoplastic is the material which become soft on heating and hard on cooling several times.
Therefore, they can be recycled.

Plastic has light weight, lower price, good strength and easy to handle. Therefore, container are made from plastic.

Polyethylene is a thermoplastic polymer consisting of long hydrocarbon chains. Polyethylene or polythene is the most common plastic. Its primary use is in packaging (plastic bag, plastic films, containers including bottles, etc.).

Plastic is a material consisting of synthetic or semi-synthetic organics that can be moulded into solid objects of diverse shapes. Plastics are typically organic polymers of high molecular mass, but they often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, but many are partially natural.

Melamine is poor conductor of heat and resists fire. Most of the synthetic fibres are poor conductors of heat and electricity. However, melamine is used as a coating on the uniforms of firemen as they are flame resistant.

Thermosetting plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. It can't be recycled. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermosetting ideal for high-heat applications such as electronics and appliances.

Plastic is a poor conductor of heat and electricity. 

Most plastics are both thermal and electrical insulators, meaning they show high resistance to electrical current and are poor conductors of heat.

Handles of most pans are made up of thermosetting plastic. Thermosetting plastic does not melt easily. These plastic cannot be reshaped again and again.

The world's first fully synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term 'plastics'. Bakelite is made from carbolic acid (phenol) and formaldehyde and is referred to as a phenolic resin. Bakelite was the first thermosetting plastic.

Nylon was first commercially synthesized fibre. The production of nylon was started almost simultaneously in New York and London, thus it got its name (NY for New York and Lon for London) as nylon. Nylon is synthesized from coal, water and air. Fibre of nylon is very strong and it also resembles silk.

A thermosetting plastic, also known as a thermoset, is a polymer material that irreversibly cures. The cure may be induced by heat, generally above $200^o C$ $(392\ F)$, through a chemical reaction or a suitable irradiation.
$Bakelite$ is one example of this type.

Most of the plastics are non-biodegradable.

Polymer of styrene and vinyl chloride (polystyrene and PVC)  can be repeatedly melted and re-molded into new products and are 100% recyclable. 

Melamine have properties to interfere with the combustion in many different ways. Moreover, it can withstand high temperature, it is corrosion resistant and easy to handle.

Thermosetting polymers are formed from monomers of viscous state which changes irreversibly on heating into an infusible insoluble polymer. They have high crosslinks due to which they are rigid.

Plastics are non-reactive at room temperature and others are highly reactive.

Terylene is a synthetic polymer formed by the condensation polymerization reaction of terephthalic acid and ethylene glycol with the release of a methanol molecule. 

Thermoplastic polymer can change their properties when heated and cooled. All plastics are bad conductors of heat and electricity.

The properties of the plastics are as follow:

Melamine is a thermosetting plastic that is highly resistant to heat, making it ideal for fireproof coatings and kitchenware.

Thermosetting plastics undergo a chemical change during molding that makes them rigid and unable to be softened by heat again.

(i) Saucspan handles are made of bakelite as it is a bad conductor of heat.
(ii) Bakelite is also a bad conductor of electricity so the electric plugs, switches, etc. are made of it.

Since plastics do not react with water and air, they are noncorrosive in nature and are thus used for storage.

Bakelite is an example of thermosetting plastic which is also a poor conductor of electricity. Due to its insulating character, it is used for switches and other electrical insulators.
Option B is correct.

The given statement is true. Plastics are resistant to corrosion and chemicals.

Thermoplastics are linear polymers. They are also known as thermosoftening plastics because they become malleable when heated. Although they are pliable above a certain heat threshold, they return to a solid once they have been sufficiently cooled. For this reason, thermoplastics are put to unique uses in a number of manufacturing and engineering industries.

Apart from their primary characteristics, thermoplastics vary slightly in usage and properties. For example, polystyrene is a hard, water-resistant thermoplastic, according to BBC. This makes it an excellent choice for creating toy models and for packaging that will not be exposed to extreme heat sources in transit. Polymethyl methacrylate is also a stiff thermoplastic, but it is also an electrical insulator and can be polished well, so it is often used in vehicle windows and light covers.

Bakelite is a classic example of a thermosetting plastic, used historically for electrical insulators and telephone casings.

Disposable cups are made up of thermocol. It is a synthetic petroleum product which is made by restructuring of the chemical bonding of the polystyrene, to develop a stretch polystyrene. In this process, thermoplastic granules are expanded through the application of steam and air. The expanded granules become large and light in weight.

Thermosetting plastics: Which on heating becomes infusible these cannot be reused.Ex- Bakelite,urea formaldehyde resin.

Synthetic fibres are created by extruding fibre forming materials through spinnerets into air and water, forming a thread. These artificially manufactured fibres were made from polymers obtained from petro chemicals. These fibres are called synthetic or artificial fibres. The two most common ones are nylon and polyester. Nylon is made from two chemicals, adipic acid (AA) and hexamethylene diamine (HMD).

Plastics are not chemically reactive and they are non-corrosive. So, most of the plastics are resistant to strong acids and alkalies. Hence the given statement is True.

Celluloid, which is considered the first thermoplastic, made its appearance in the mid- 1800 s and reigned in the industry for approximately 100 years. During its peak production, it was used as a substitute for ivory. Today, it is used to make guitar picks.

Vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials via the addition of sulphur or other equivalent curatives or accelerators. Cross-linking introduced by vulcanization prevents the polymer chains from moving independently. As a result, when stress is applied the vulcanized rubber deforms, but upon release of the stress it reverts to its original shape.

Polyamide (nylon) is a thermoplastic, not a thermoset plastic, as it can be melted and reshaped.

Bakelite is a thermosetting plastic which is one of the first plastic made from synthetic components. Bakelite was used for its electrical non-conductivity and heat-resistant properties in electrical insulators, radio, and telephone casings.

Polystyrene foam also known as Styrofoam is brittle in tension, lightweight, with good heat and sound insulation. It is available in blocks and used for product-modelling.

Plasticity,  ability of certain solids to flow or to change shape permanently when subjected to stresses of intermediate magnitude between those producing temporary deformation, or elastic behaviour, and those causing failure of the material, or rupture.

Plastics are insoluble in water and it cannot be dissolved in water.

When plastics are burnt toxic substances are released into $air$ causing air pollution. The sentence is self-explanatory.

Most of the commonly used household electronics like freezers, washing machine, etc are made of plastic since it is the bad conductor of electricity.

Thermosetting polymers: These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are polysiloxanes, bakelite, urea- formaldehyde resins, etc.

Thermosetting plastic consists of chain of the  molecules which are cross-linked, with each other when heated. When thermosetting plastics cross-link, the molecules create a permanant, network  which is a $3-D$ structure and can be considered one giant molecule. Once cured, thermosetting plastic cn not be remelted, in the same way that cured concrete cannot be reset. 

Garden chairs made of plastic strips and plastic articles get faded, worn out and cracked in sunlight, mainly because of UV rays. All types of UV can cause a photochemical effect within the polymer which can lead to degradation of some sort to the materials. Absorbed UV energy can exits the photon in a plastic, exciting the photons can create free radicals. Those free radicals can cause breaks in the polymer bonds.

Thermosetting polymers have different properties to thermosoftening polymers. Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily.

 Plastics are high molecular weight (macromolecular or polymeric) organic substances that are synthesized from low molecular weight compounds. 

Teflon is a synthetic polymer of polytetrafluoroethylene that can be used to cover the surface of a certain object and imparts nonstick properties to it.  

Plastics are categorized into thermosoftening/thermoplastic and thermosetting/thermoset plastics.

Plastics are categorized into thermosoftening and thermosetting plastics.
In thermosoftening plastics, the forces between the polymer chains are weak, so they can easily be remoulded into new shapes. This makes it possible to recycle this type of plastic. whereas in thermosetting plastics there are strong covalent bonds forming cross-links between the polymer chains, making these plastics hard and rigid. Once set into its original shape, a thermosetting plastic can't be softened and remoulded. The strong bonds between polymers also mean that thermosetting plastics are much more heat resistant than thermosoftening ones.
Example: Melamine is an example of a thermosetting plastic and polythene is a thermosoftening plastic.
Option A is correct

Bakelite is prepared in laboratories by controlling the pressure and temperature applied to phenol and formaldehyde. 

When plastics are burnt toxic substances are released into the air causing air pollution. Hence, the given statement is false.

Biodegradable substances are such materials which are and can be
degraded by natural factors like microbes (e.g. bacteria, fungi and few
more), abiotic elements like temperature, UV, oxygen, etc.
Unlike
biodegradable, non-biodegradable substances like plastics, cannot be
easily handled and cannot be decomposed or dissolved by natural agents.
Option A is correct

Plastics are human-made polymers and are non-biodegradable which means they cannot be easily handled and cannot be decomposed or dissolved by natural agents like microbes (e.g. bacteria, fungi), abiotic elements like temperature, UV, oxygen, etc. Thus are not eco-friendly.
Option B is correct

The plastics are the non-biodegradable wastes because they are synthetic polymers which cannot be acted upon by the microbes. They cannot be degraded by the decomposition activity of the bacteria and fungi. The cotton, paper and leftover food are degradable.