Paper Making Process

Wood is made up of cellulose fibres that are bound together by lignin in order to produce paper, these fibres must be seperated from one another to form mass individual fibres called wood pulp

Softwood Fibres - longer, llightweight & offer greater strength
                            - they contain a grain that makes them a harder to shape 

Hardwood Fibres - shorter, offer a smother, opaques finish 
                             - their close grain procide highly deocrative surface finishes 

After de-barking hard and soft wood logs are cut into 2cm chips along the grain. these arepounded into fragments and are screened. the resulted pulp is stored and treated with either acid or alkali to break down the lignin.

Advantages:

• provides a 90% yield from teh pulpwood as it uses the whole of the log except for the bark.
• investment costs for mechincal pulp mills are realtively low in comparsion with other types of mill.
• well suited for 'bulk' grades of paper; i.e newsprint and packaging boards.
• can be bleached to produce higher value-added products.

Disadvantages:

• Llower strength characteristics than softwood chemical pulps
• Paper can 'yellow' when exposed to bright lights due to high lighin content.

The logs of coniferous trees are saturated with water and de-barked. the wood is ground down. this softens the lignin and the mechanised forces seperate fibres to form groundwood pulp. this pulp is screened to accept 1-2mm pieces with larger pieces being re-circulated for additional screening.

Advantages:

• provides a 90% yield from teh pulpwood as it uses the whole of the log except for the bark.
• investment costs for mechincal pulp mills are realtively low in comparsion with other types of mill.
• well suited for 'bulk' grades of paper; i.e newsprint and packaging boards.
• can be bleached to produce higher value-added products.

Disadvantages:

• lower strength characteristics than softwood chemical pulps
• paper can 'yellow' when exposed to bright lights due to high lighin content.

Waste pulp is often mixed with virgin fibres to produce better quality apers as gibres become shorter and weaker an lose their papermaking properties. Manufacturers blend a variety of pulp and process them along with bonding agents and coloured pigments to produce paper with different qualities

Advantages:

• makes use of recycled papers, which are a sustainable resource.
• well suited fro 'bulk' grades of paper; i.e. newsprint, tissue and packaging boards.

Disadvantages:

• cannot be recylced indefinitely as pulp loses quailty - virgin pulp needs to be added.
• does not save any more ebergy in processing than other methods
• requires considerable processnig and additives to produce good-quailty paper.

Wet End
Starts with the wood pulp diluted to 99% water and 1% fibre. a continous stream of slurry is pumped through an ajustible slit onto a moving guaze wire belt that vibrates to drain off some of the water and allow the fibres to interweave.

Press Section
Nip presses or rollers that wring out the majority of excess water from the pulp and stretches out into a rough paper.

Dryer Section
Dries the paper using a series of steam-heated rollers by removing the moisture.

Calender Section
Paper is fed into a series of rollers to smooth it out and give it a thickness. the amount of pressure determines the finish of the paper.