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PULP GRADES

Pulp grades are classified according to their production process.

Mechanical Pulp
Semi-Chemical Pulp
Chemical Pulp
De-inked Pulp

MECHANICAL PULP

Stone Groundwood pulp: pulp produced by grinding wood into relatively short fibres. This pulp is used mainly in newsprint and wood-containing papers, like LWC (light weight coated) and SC (super-calendered) papers.

Thermo-mechanical pulp (TMP): pulp is produced in a thermo-mechanical process where wood particles are softened by steam before entering a pressurised refiner. TMP has mainly the same end-uses as Stone Groundwood pulp. Variants of the above two processes are pressurised Stone Groundwood pulp and Refiner Mechanical pulp.
 
 

SEMI-CHEMICAL PULPS

Semi-chemical: pulp produced in a similar way to TMP (Thermo-mecanical pulp), but the wood particles are chemically treated before entering the refiner. This pulp has properties suited to tissue manufacture. Some (Chemi-thermo mechanical pulp) CTMP pulp is used in printing and writing grades. CTMP pulp is classified under semi-chemical pulps in the Harmonised System of the Customs Cooperation Council. In the Food and Agricultural Organisation (FAO) of the United Nations, as well as other industry statistics, such Chemi-thermo mechanical pulps are gruped with mechanical pulp.
 
 

CHEMICAL PULPS

Sulphite: pulp produced by cooking wood chips in a pressure vessel in the presence of bisulphite liquor. End-uses range from newsprint, printing and writing papers, tissue and sanitary papers. Sulphite can be either bleached or unbleached.

Sulphate (or kraft): pulp produced by cooking wood chips in pressure vessels in the presence of a sodium hydroxide (soda) liquor. The pulp may be unbleached or bleached. End-uses are widespread, with bleached pulp particularly used for graphic papers, tissue and carton board, wrappings, sack and bag papers, envelopes and other unbleached speciality papers.
 
 
 

DE-INKED PULPS:

Pulp made from recovered paper from which inks and other contaminants have been removed.
 
 

PULP PRODUCTION

PULP MILL

Trees provide the primary raw material for the paper and board industry. Wood is made from cellulose fibres that are bound together by a material called lignin. In a pulp mill, the fibres are separated from one another into a mass of individual fibres. After separation, the fibres are washed and screened to remove any remaining fibre bundles. The pulp may then be used directly to make unbleached papers, or bleached for white papers. Pulp may be fed directly to a paper machine in an "integrated paper mill" or dried and pressed into bales to be used as a raw material by paper mills worldwide.

The pulp-making process

1. Timber and de-barking

 2. Chipping machine and pulping process

3. Cleaning and bleaching
 

 
 
4. Bleaching, washing and drying

 

Chemical pulp is stronger, but more expensive than mechanical pulp

Using chemical pulp is more expensive to produce paper than mechanical pulp or recovered paper, but it has better strength and brightness properties. Softwood kraft pulp is used to provide the required strength when producing light-weight publication papers. Fine papers (e.g. copy papers, writing papers, etc.) are an example of the type of paper produced mainly from hardwood pulp, which is reinforced by a minor amount of stronger and more expensive softwood kraft pulp. Pine and spruce provide the strongest pulp (e.g. softwood kraft), while hardwood kraft is produced from birch, eucalyptus, aspen, acacia and many other mixed tropical species.

Today, the fast growing species of tree (such as planted eucalyptus and acacia) are the most rapidly-growing pulp raw material.

	Mechanical Pulp	Chemical Pulp
Energy consumption	1000 KW/ton of pulp	Self-sufficient
Yield (from wood material)	95%	45%
Fibre length	Fibres broken	Mainly longer fibres
Paper strength	Lower	High
Production costs	Lower	Higher than in case of mechanical pulp