Polyurethanes, Cellulose-Polyacrylonitrile, Chemistry tutorial

Introduction

If we are sitting on a padded chair right now, the cushion is more than probable made of polyurethane foam. Cellulose is one of many polymers found in nature. Wood, paper, and cotton all have cellulose. Cellulose is an outstanding fibre.

Definition of Polyurethane, Cellulose and Polyacrylonitrile

Polyurethanes are the most famous polymers utilized to create foams. Polyurethanes are more than foam. Cellulose is made of repeat chapter of the monomer glucose. Polyacrylonitrile is a vinyl polymer, and a derivative of the acrylate family of polymers.

Polyurethanes

Polyurethanes are the single most adaptable family of polymers there is. Polyurethanes can be elastomers, and they can be paints. They can be fibres, and they can be adhesives. Wonder fulbizarre polyurethane is spandex. Of course, polyurethanes are termed polyurethanes since in their backbones they enclose a urethane linkage.

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Fig: Polyurethanes  

The structure above illustrates easy polyurethane, but polyurethane can be any polymer enclosing the urethane linkage in its backbone chain.

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Fig: urethane

More sophisticated polyurethanes are feasible, for instance Polyurethanes are made through reacting diisocyanates with di-alcohols;

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Fig: ethylene glycol

Sometimes, the dialcohol is replaced through a diamine, and the polymer we obtain is a polyurea, since it encloses a urea linkage, relatively than a urethane linkage. But such are generally termed polyurethanes;

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Fig: ethylene diamine

Polyurethanes can hydrogen bond extremely well and therefore can be extremely crystalline. For this reason they are frequently utilized to build block copolymers via soft rubbery polymers. Such block copolymers have properties of thermoplastic elastomers.

Spandex

One unusual polyurethane thermoplastic elastomer is spandex that DuPont sells under the trade name Lycra. It has both urea and urethane connections in its backbone. What provides spandex its special properties is the fact that it has rigid and soft blocks in its repeat structure. The short polymeric chain of a polyglycol, generally about 40 or so repeats units long, is soft and rubbery. The rest of the repeat chapter, the stretch by the urethane linkages, the urea linkages, and the aromatic groups, is extremely rigid. This section is stiff sufficient that the rigid sections from diverse chains clump mutually and align to form fibres. Of course, they are unusual fibres, as the fibrous domains formed via the stiff blocks are linked mutually through the rubbery soft sections. The consequence is a fibre that acts like an elastomer! This permits us to make fabric that stretches for exercise clothing and the like.

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Fig: soft rubbery segment

Cellulose

Cellulose is 1 of many polymers originate in nature. Wood, paper, and cotton all enclose cellulose. Cellulose is an outstanding fibre. Wood, cotton, and hemp rope are all made of fibrous cellulose. Cellulose is made of repeat chapter of the monomeric glucose. This is the similar glucose that the body metabolizes in order to live, but we can't digest it in the form of cellulose. Since cellulose is built out of a sugar monomer, it is termed a polysaccharide

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Fig: glucose

Cellulose has a significant place in the story of polymers since it was utilized to create several of the 1st synthetic polymers, as cellulose nitrate, cellulose acetate, and rayon. Another cellulose derivative is hydroxyethyl cellulose. It differs from plain old regular cellulose in that several or all of the hydroxyl groups of the glucose repeat unit have been replaced by hydroxyethyl ether groups.

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Fig: hydroyethylcellulose repeat unit

Such hydroxyethyl groups get in the way when the polymer tries to crystallize. Because   it can't crystallize, hydroxyethyl cellulose is soluble in water. In addition to being a great laxative, it's utilized to thicken shampoos too. It as well makes the soap in the shampoo less foamy, and assists the shampoo clean better through forming colloids around dirt particles.

Normally, particles of dirt are insoluble in water. But a chain of hydroxyethyl cellulose can wrap itself around a dirt particle. This mass can be thought of as a snack cake, through the polymer chain as the cake and the dirt as the creamy filling. This snack cake is soluble in water, so through enveloping around the dirt like this, the hydroxyethyl cellulose tricks the water into accepting the dirt. In this way, the dirt obtains washed away instead of being deposited back onto our hair.

Polyacrylonitrile

Polyacrylonitrile is utilized for extremely few products an average consumer would be recognizable by, except to make another polymer, carbon fibre.

Homopolymers of polyacrylonitrile have been uses as fibres in hot gas filtration systems, outdoor awnings, sails for yachts, and even fibre reinforced concrete. But frequently copolymers enclosing polyacrylonitrile are utilized as fibres to build knitted clothing, as socks and sweaters, in addition to outdoor products like tents. If the label of several piece of clothing says 'acrylic', then it is made out of several copolymer of polyacrylonitrile. Generally they are copolymers of acrylonitrile and methyl acrylate, or acrylonitrile and methyl methacrylate:

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Fig: poly (acrylonitrille -co-methyl methacrylate)

As well, sometimes we make copolymers of acrylonitrile and vinyl chloride. Such copolymers are flame-retardant, and the fibres made from them are termed modacrylic fibres.

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Fig: poly (acrylonitrile-co-vinyl chloride)

But the slew of copolymers of acrylonitrile doesn't end there also. Poly (styrene-co-acrylonitrile) (SAN) and poly (acrylonitrile-co- butadiene-co--styrene) (ABS), are employed as plastics.

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Fig: SAN

SAN is an easy arbitrary copolymer of styrene and acrylonitrile. But ABS is more complicated.  It's made through polymerizing styrene and acrylonitrile in the occurrence of polybutadiene.  Polybutadiene has carbon-carbon double bonds in it that can polymerize, too. So we end up through a polybutadiene chain by SAN chains grafted onto it.

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Fig ABS

ABS is extremely strong and lightweight. It is strong enough to be used to make automobile body parts. Using plastics like ABS makes automobiles lighter, so they use less fuel, and therefore they pollute less.  ABS is a stronger plastic than polystyrene because of the nitrile groups of its acrylonitrile units. The nitrile groups are very polar, so they are attracted to each other. This permits conflicting charges on the nitrile groups to stabilize each other. This strong attraction holds ABS chains mutually tightly, making the material stronger. As well the rubbery polybutadiene builds ABS tougher than polystyrene.

Polyacrylonitrile is a vinyl polymer, and a derivative of the acrylate family of polymers. It is made from the monomer acrylonitrile via free radical vinyl polymerization.

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Fig: polyacrylonitrile  

Polymers an Application

Table: Plastics and Fibre Polymers

Polymers used as plastics

Polymers used as fibres

Polypropylene

Polypropylene

Polyesters

Polyesters

Polystyrene

Polyethylene

Polycarbonate

Kevlar and Nomex

PVC

Polyacrylonitrile

Polyethylene

Cellulose

Poly(methyl methacrylate)

Polyurethanes

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