Chemical Industries

Detergents

Definition

The term detergent derives from the Latin word “detergere” meaning “to wipe off””. Detergents are the non-soapy or soapless synthetic cleansing agents (or products) which enhance the cleaning effect of water used for cleaning grease and dirt from any fabric or a solid surface and for washing a variety of utensils. Detergents are complex organic compounds with long chain molecules which are salts of organic sulphonic acids. Stated differently, detergents are sodium or potassium salts of long chain-alkyl or aryl sulphonated acids and are used as a better cleansing agents than soaps as they do not form scum with hard water unlike soap (because they react with Ca²⁺ or Mg²⁺ ions of salts present in hard water thereby producing respective water soluble compounds in which dirt and grease are readily carried away). They have general formula R –OSO₃^–Na⁺ or R – C₆H₄ – SO₃^–Na⁺ or R – C₆H₄ – OSO₃^–Na⁺. [Non-aqueous detergents also have been developed which increases the cleansing action of organic solvents].

Examples/Types of detergent

Detergents have general formula R –OSO₃^–Na⁺ or R – C₆H₄ – SO₃^–Na⁺ or R – C₆H₄ – OSO₃^–Na⁺ where R is a chain of 12 to 18 carbon atoms.

Examples/Types of detergent

Structure (or Composition) of a detergent

A molecule of a detergent has the same basic structure as soap which is made up of following two parts:

1. Hydrophobic Part

It is a non-polar, water-repellent and oil-soluble part of detergent comprising of covalently bonded long hydrocarbon chains (of 12-18 carbon atoms) or ring structure group forming the tail of the detergent. It is also called hydrocarbon end. Being non-polar in nature, it attracts the non-polar oil and grease. The hydrocarbon chain is obtained from petroleum.

2. Hydrophilic Part

It is a polar, water-loving and water-soluble part of detergent comprising of small ionic (anionic or cationic) groups such as sulphonate (–SO₃^- or SO₃^2- or –SO₃^-Na⁺), sulphate (–OSO₃^- or SO₄^2- or –OSO₃^-Na⁺), quaternary ammonium groups (NR4+ e.g. [NR₄]⁺Cl, [NR₄]⁺Br etc) or hydroxyl group (– OH) forming the head of the detergent. It is also called polar or ionic end. Being polar in nature, it dissolves in polar water thereby decreasing the surface tension of water increasing its wetting ability. The ionic groups (SO₃^2- or SO₄^2-) are introduced synthetically by means of concentrated sulphuric acid.

 Mechanism of cleaning action of detergent

Detergents function in the same way as soaps. Its hydrophobic hydrocarbon non-polar tail dissolves the oily layer (grease, oil or ghee) to remove them from clothes, as both are non-polar while its hydrophilic sulphate or sulphonate polar head dissolves in water as both are polar thereby decreasing the surface tension of water increasing its penetrating or wetting ability, so that slight stirring of water removes the grease which is carried away with water along with dirt.

Distinction between Soap and Detergent

Soap is the sodium or potassium salt of fatty acids which produces insoluble salts in the form of ppt. in hard water. Soaps are anionic surfactants as they ionize to give anionic carboxyl group of fatty acid which forms water insoluble salts with heavy metals, thus soap does not work well in hard and acidic water.

Detergents differ from ordinary soap in many respects:

1).    Detergents are the sodium or potassium salts of alkyl or aryl sulphonated acids which does not form a scum with hard water unlike soaps which are sodium or potassium salts of fatty acids.

2).    Detergents are anionic or cationic or non-ionic surfactants while soaps are anionic surfactants.

3). Detergents are synthetic products prepared from hydrocarbons obtained from petroleum while soaps are natural products prepared from oils which are becoming scarce. Thus synthetic detergents help us to save oils.

4).   Synthetic detergents can be used for washing even in hard water as they form water soluble salts with heavy metals ions (Ca²⁺, Mg²⁺, Fe²⁺ etc) while soaps do not work well in hard water as they produce water insoluble salts in the form of curdy ppt. with heavy metal ions which stick to the fabric.

5). Synthetic detergents have better and stronger cleansing power than soaps.

6).     Synthetic detergents can be used even in the acidic solution while soaps cannot be used in acidic solutions as they decompose under acidic conditions to give free acids.

RCOONa(s)

+

H+(aq)¾¾¾¾®

RCOOH(aq)

+

Na+(aq)

Composition

1.	Surfactant/ Surface active agent	[ABS or LAS]	;	15-25%
2.	Builders/Antidepositing agent [condensed sodium triphosphate]		;	30-40%
3.	Auxillary agent /Additives:
	a).Foam stabilizers (similar to detergent in structure)
	b). Optical brighteners	(colourless dyes which deposit irreversibly on fabric)
	c). Antiredeposition agent	(prevent redeposition of dirt on cloth during washing)

           Synthetic Fibres                  Dr Inam Ul Haq Jazbi

Definition and importance of Synthetic Fibres  

Synthetic fibres are the man-made fibres which are the co-polymers prepared by the condensation polymerization of two different substances with the elimination of water molecules. Their advantages are:

1.      Lightness of weight                  

2.      Ease of ironing                           

3.      Softness

4.      Heat retention                  

5.      Heat conductivity

Classification of Synthetic Fibres

1.	Nylon 6.6	;	(Nylon fibre)
2.	Terylene	;	(Polyester fibre or Dacron)
3.	Acrylic fibre	;	(synthetic fibres derived from acrylonitrile), polyacrylonitrile
4.	Rayon fibre	;	(synthetic fibres derived from cellulose)
	a) Viscose rayon	;	(sodium cellulose xanthate)
	b) Acetate fibre	;	(cellulose acetate)
	c) Nitrocellulose fibre	;	(cellulose nitrate)

1. Rayon

The term Rayon is the name given to all synthetic fibres which are derived from cellulose. Rayon is considered as the man-made or synthetic fibre. e.g. viscous rayon, nitrocellulose, cellulose acetate, cupra silk etc. Rayon was discovered by a French scientist Chardonnet in 1884. [He was investigating the silk worm disease. Rayon is a fibre obtained mechanically from silk worms. The starting material is cellulose. The silk worm on mulberry tree eats cellulose, digests it and changes it into silk which comes out in a viscous form and solidifies on contact with air and becomes silk thread. Man does the same with cellulose, when preparing silk mechanically]. 

Viscous rayon

Viscous rayon is manufactured from cellulose when it is digested with sodium hydroxide solution. When carbon disulphide is passed through the solution, a mixture of sodium cellulose xanthate is formed which is soluble in NaOH solution. Due to very high viscosity, the silk thus obtained is called viscous rayon. The solution is forced through sulphuric acid bath where cellulose is precipitated as fine threads. This artificial silk is cheaper than cellulose acetate silk or nitrocellulose silk. 

2. Nylon or Nylon 6.6 (polyamide)

Nylons are the synthetic fibres which contain long chain polyamide as fibre forming substance. Nylon is a condensation polymer of double acid adipic acid (hexane-1,6-dioic acid) and double amine hexamethylene diamine (1,6-diaminohexane). Thus nylon is a polyamide [The same type of linkage is found in proteins]. The name nylon 6.6 is derived from the fact that both joining components contain six carbon atoms each. [It is different from natural silk in its structure but similar in appearance. It is more elastic and finer in texture than silk. It is used in hosiery where rayon has failed due to its inelasticity].                                           

 3. Terylene or Dacron or Polyethylene terephthalate

Terylene is a synthetic polyester fibre which contains long chains polyesters as fibre forming substance. Terylene is a condensation polymer of ethylene glycol (ethane-1,2-diol) and aromatic double acid terephthalic acid (benz-1,4-dioic acid or benzene-1,4- dicarboxylic acid). [Since an acid and an alcohol react to form an ester, hence this fibre is also called polyester fibre]. Thus terylene is a polyester [The same type of linkage is found in fats, oils and waxes]. It is produced by the condensation polymerization of ester formed by the esterification of terephthalic acid and ethylene glycol. [It is more resistant to water and has better sweat absorbing quality than nylon. Its fabrics have more strength, resistant to heat, better texture and tailoring qualities]. The trade name of terylene is Dacron.      

Glass

Definition and General Characteristics of Glass

Glass is one of most important artificial silicates which is a non-crystalline, extremely viscous super-cooled liquid (i.e. a solid solution without crystallization) having no definite melting point and sufficiently high viscosity to prevent crystallization. Chemically, glass is a mixture of alkali and alkaline earth’s silicates (containing silicates and borates of other metals also) having random structure.

1.    It is a transparent/translucent amorphous substance, which is obtained by fusion of various metallic silicates.

2.    Glass is not a true solid because molecules are not arranged in a definite pattern. In fact, glass is super-cooled liquid i.e. a solid solution without crystallization. Thus in glass, molecules are arranged in random positions as in case of liquids. That is why a glass does not have sharp melting point. On heating, it gradually becomes more and more plastic in nature.

Chemical Nature

Chemically, glass is a mixture of various components, so it has no particular formula. However, it can be represented by approximate general formula; A₂O.A’O.6SiO₂:

Where;    

A    = Alkali metal            e.g. Li, Na, K                                        

A’   = Bivalent metal       e.g. Ca, Ba, Pb, Zn

Annealing and Etching

The slow gradual cooling of fused glass to avoid fractures in glass is termed as annealing.

Hydrofluoric acid (HF) attacks the glass. This property is used to make designs on glass and this process is called etching.

Manufacture of ordinary Soft glass or Soda glass

Ordinary Soft glass or Soda glass (Soda-Lime silicate) is a mixture of sodium silicate and calcium silicate. It is prepared by heating sand, soda ash and lime stone together in a furnace at 1400°C. The refractory potassium glass used for making chemical glass wares is obtained by using potash ash or pearl ash (K₂CO₃) instead of soda.

	Na2CO3	+ SiO2 ¾¾®Na2SiO3 + CO2
	CaCO3	+ SiO2¾¾®CaSiO3    + CO2
OR
	Na2CO3	+ 6SiO2  + CaCO3 ¾¾®Na2O.CaO.6SiO2+2CO2

Different Types of Glass

1.	Ordinary Soft glass/Soda glass	;	Soda-Lime(Na-Ca) silicate, used for window glass, bottles etc.
2.	Hard glass/Refractory potash glass	;	Potash-Lime (K-Ca) silicate, used for hard glass apparatus.
3.	Flint or Optical glass	;	Potash-Lead (K-Pb) glass, used for making optical devices.
4.	Jena glass	;	mixture of zinc and borosilicate, Heat resistant glass
5.	Pyrex glass/Borosilicate glass	;	mixture of sodium-aluminium borosilicate, a heat resistant glass.
6.	Safety/Unbreakable glass	;	layer of plastic is sandwiched b/w two glass layers, shatter-proof
7.	Coloured glass	;	obtain by adding certain metallic oxides to an ordinary glass.
	i).      CuO gives light blue colour. ii).     CoO gives blue colour. iii).    Cr2O3 gives green colour. iv)     SeO and ZnO give red coloured glass.

Composition of glass

90% of world glass out put is made up of sand, soda ash and lime. There are more than one thousand formulations depending upon the properties and uses of glass. Almost all glass contains following three basic constituents:

1.	Formers	(form basic glassy structure)	[Silica,SiO2 or oxides of B/Ge/ P/As]
2.	Fluxes/Modifiers	(reduce melting point of silica)	[ Oxides of Na/Ba/Li]
3.	Stabilizers/ Intermediates	(reduce chemical reactivity of glass)	[ Oxides of Ca/ Al/ Zn]

Raw Materials Used in glass manufacturing

I.	CULLET:	These are small broken pieces of scrap glass. They decrease m.p. of other raw materials.
II.	BATCH:	It is a homogeneously ground mixture of following:
	1. Sand	;It is a source of silica(purified silica of uniform size is used)
	2. Alkali metals	;Na is used in the form of Na2CO3 or Na2SO4.K2SO4/KNO3 is source of K.
	3. Alkaline Earth’s	;Lime (CaO), lime stone (CaCO3) or BaCO3 provides required alkaline earth
	4. Heavy metals	; Red lead (Pb3O4) is used as a source of lead. ZnO is a source of zinc.
	5. Borax	; It acts as a flux and also increases durability of glass.
	6. Colouring materials	; Transition metal oxides is used to give different colours in glass. e.g.:
		i)      CuO    gives light blue colour.
		ii)       CoO    gives dark blue colour.
		iii)      Cr2O3   gives green colour.
		iv)      Cu2O    gives red colour.
		v)       MnO2    gives violet colour.
		vi)      CdS    gives lemon yellow colour.
		vii)     SeO and ZnO give red coloured glass.

Basic Steps of glass manufacturing

1. Fusion or Melting of raw materials.

2. Forming or shaping of articles.  (By blowing or moulding either manually or mechanically)

3. Annealing                                      (is slow gradual cooling of fused glass to avoid fractures in glass)

4. Finishing                                       (includes cleaning, grinding, polishing, cutting etc.)

5. Etching                                      (HF attacks the glass. This property is used to make design on glass)

Plastics                     Dr Inam Ul Haq Jazbi

Definition of Plastics

Plastics are macromolecules which are synthetic polymers (i.e. compounds build up of a large number of smaller molecules that have reacted and added with one another) that are formed in liquid state and then hardened having a structural rigidity. Plastics are organic materials of high molecular weight obtained through polymerization of smaller low molecular weight unsaturated organic compounds (monomers) of various types having a fair range of deformability and mouldability and thus can be moulded into articles of any desired shape and form by applying heat and pressure. [Plastics are light in weight, resistant to corrosion (non-corrosive) and good electrical and thermal insulators. They are not affected by acids or alkalis. They have the ability to be deformed and to be moulded].

General Characteristics of Plastics

Glass like transparency and resistance to weathering make plastics as a glass substitute (e.g. in aircraft windows, reflectors on auto vehicles, T.V. guard screens and street light fittings etc.). Plastics can be used with the same degree of assurance as metals and alloys and thus have a large number of applications because of their following characteristics:

1.      Toughness and light in weight                         

2.      Water resistance                                      

3.      Acid or alkali resistant

4.      Corrosion resistance (non-corrosive)               

5.      Remarkable colour change            

6.      Ease of fabrication

7.      Good electrical and thermal insulator             

8.      Ease of moulding

Types of Plastics

Plastics are of two types:

1. Thermo-Softening Plastics/Thermoplastics

These are the plastics which soften on heating and harden on cooling without undergoing any chemical change formed by plain or co-polymerization (addition polymerization). They can be heated again and again to soften for reshaping. Thermoplastics are linear polymers with no cross-links. These plastics do not undergo any chemical change or cross-linking on heating and therefore, they can be reheated again and again to soften for reshaping and remoulding. They include;

1.	Polyethylene or polythene	;	ethene or ethylene (CH2=CH2)
2.	Polypropylene	;	Propene or propylene (CH2=CHCH3)
3.	Polytetrafluoro ethylene (PTFE) /Teflon	;	tetrafluoro ethylene (TFE ; F2C=CF2)
4.	Polystyrene/polyvinylbenzene (PVB)	;	styrene (vinyl benzene;C6H5CH=CH2)
5.	Polyvinyl chloride (PVC; Vinyl resin)	;	vinyl chloride (CH2= CH-Cl)
6.	Polyvinyl acetate (PVA; Vinyl resin)	;	vinyl acetate (CH2=CH-OOCCH3)
7.	Polyvinylidene chloride (Vinyl resin)	;	vinylidene chloride (ClCH= CH-Cl)
8.	Perspex (Polymethyl methacrylate; PMMA)	;	methyl methacrylate (CH2=C(CH3)COOCH3)
9.	Lucite/plexglass (Polymethylmethacrylic acid)	;	methyl methacrylic acid(CH2=C(CH3)COOH)

2. Thermo-Setting Plastics

These are the plastics which soften on heating and permanently harden on continuous heating. These plastics undergo chemical changes on heating and therefore, cannot be softened again by heating. They are formed by condensation polymerization. They include Bakelite resin, urea-formaldehyde resin, melamine-fomraldehyde resin

1.	phenol-fomraldehyde resin/Bakelite
2.	urea-formaldehyde resin
3.	melamine-fomraldehyde resin
4.	expoxy resins (adhesive araldite)

Basic Materials and their sources (Additives in plastics)

Petrochemicals provides the basic constituent of a plastic; the polymer. In addition, one or more additives are added to give desired qualities to plastic which include:

1.	Petrochemicals	;	(providing the basic constituent , polymer)
2.	Reinforcing Agents	;	Increase the mechanical strength of plastic including glass fibers, graphite, aromatic nylon, Boron.
3.	Fillers	;	Increasing the volume (saving costly polymer) and mechanical strength and make plastic fire resistant. eg. coal, wood, flour, cotton, saw dust.
4.	Stabilizers	;	Prevent chemical degradation (decomposition) of plastics.
5.	Plasticizers	;	Reduce the brittleness and improve the elasticity of plastic.
6.	Pigment & Dyes	;	Impart colour to plastic. (TiO2 gives brilliant white plastic).
7.	Flame Retardants	;	Increase thermal insulation. e.g. Chlorine, bromine etc.