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Chemistry > Paper > Flashcards

Paper Flashcards

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1
Q

What is wood

A

Composed of cellulose fibres in a lignin matrix

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2
Q

What does cellulose fibres give to wood

A

Tensile strength

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3
Q

What does the lignin matrix give wood

A

Compressive strength

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4
Q

What is cellulose

A

Linear poly glucose. It’s insoluble due to H bonding between chains

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5
Q

What is lignin

A

An aromatic highly cross linked and coloured molecule

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6
Q

Why does paper turn yellow

A

Lignin is oxidised

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7
Q

What is pulping

A

Breaking wood into fibres

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8
Q

What is mechanical pulping and what are the advantages and disadvantages of this

A

Wood is simply ground down. Still contain lignin so ages, shorter fibres so weaker paper. Higher yield.

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9
Q

Advantages and disadvantages of chemical pulping

A

Lignin removed, stronger paper due to longer fibres, low yield.

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10
Q

How is white paper achieved

A

Bleaching the pulp which will otherwise remiss brown

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11
Q

What are the conditions for the Kraft process

A

Wood chips + Na2S + H2O —-> kraft pulp

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12
Q

What is the role of HO- and HS-

A

Degrade cross linked lignin to form water soluble phenoxide fragments

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13
Q

What does lignin contain after chemical pulping

A

Conjugated chromophores

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14
Q

How is conjugation destroyed

A

By oxidising with bleach

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15
Q

What oxidising agent is used

A

Chlorine or chloromate,

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16
Q

Why is ClO3 preferred over Cl2

A

More oxidising and more selective

17
Q

How does ClO3 work

A

Oxidises esters to COOH

18
Q

How do you prevent water penetration

A

Introduce surface hydrophobic groupings known as sizing. This reduces wetting.

19
Q

Why are inorganic additives use in paper

A

Improve optical and physical properties such a density,brightness, softness and smoothness

20
Q

Why is CaCO3 used

A

Is a buffer

21
Q

How is paper made

A

Pulp diluted and sprayed onto a moving screen.
Dewatered by gravity and suction
Paper is then pressed and dried over steam filled cylinders

22
Q

Why is paper an expensive process

A

Energy intensive

23
Q

What are the two problems that occur during dewatering

A

Fillers are too small to be retained on mesh screen

Fillers also block the pores between fibres causing slower water drainage

24
Q

What is a high molecular cat ionic polymer used for

A

Glue to stick fillers to fibres

25
Q

What does the surface coating contain

A

Aq suspension of pigment eg clay or Titanium oxide

26
Q

What is the latex binder

A

Microscopic film forming polymer particles in water

27
Q

What occurs in the latex binder

A

Surface coating applied using a blade

Paper is super calendered to align clay platelets and improve gloss

Chemistry (22 decks)

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