May 20, 2014

Biomaterial Science（Schedule）

EG60411

Bio-Material Science
Toshiharu Enomae

Professor, PhD, Paper Device and Eco-friendly materials

2G103, 10:10-11:25, Tuesday

Papermaking - wire section
Twin-wire machine

Fourdrinier machine

Felt

Cylinder machine

Web
CylinderQ. What is a merit ofCylinder machine?

#DateContent

1

4/15

History of papermaking

24/22

Pulps – Beating and fiber properties

35/9, Fri

Pulps – Additives and functions

4

5/13

Papermaking processes & interfiber bonding

55/20

Paper– Structural and absorption properties

65/27

Paper– Mechanical and optical properties

76/3

Polysaccharide chemistry by Assoc Prof Akiko Nakagawa

8-9

6/10, 17

Pulping science and technology by Professor Hiroshi Ohi

106/24

Recent trend of paper science and technology

Papermaking – (wet) press section
A wet web is pressed at high pressure
between large rolls to squeeze out excesswater.
Water transfers to felts that sandwich thewet web.
Pressing increases
density and wet web
strength.
The common numberof nips is 3 or 4.
Kodak Historical Collection #003 (1986)

Papermaking – (wet) press section

Papermaking – dryer sectionSteam-heated cylinders dry the paper with canvases.
Free water evaporates, between fibers first , inside
fibers second, and between fibrils last .
At less than 9 % moisture content, bonding water
evaporates, forming interfiber bonds.
PaperCanvas (felt)

Drying cylinder
for felt
Dryingcylinder
PaperCanvas (felt)
Vietnam Paper Corporation (2014)

Biomaterial Science by Toshiharu Enomae1

May 20, 2014

Papermaking – calender section

Papermaking – calender section

A number of rolls press the passing paper.
They make the paper surface extra smooth and glossywith friction, and provide a higher density and more
uniform thickness

Supercalender
Soft nip calender

Types of chemical bondPapermaking – calendering effect

Paper gloss, %Number of passed nips

Basepaper

Coat layer

Number of passed nips

The number of nips is occasionally more than 10.
Q. Why is it as many as 10 although only 3 or 4 for wet press?

Inter-fiber bondInter-fiber bondEffect of water on interfiber bond formation

Interfiber approach and hydrogen bondformation due to water evaporation
Cellulose surface

Fiber

H-O-H

L µm

H-O-H

Fiber

H-O-HQ. Suppose twocrossing flat fibers withthe square , length L ona side at the crossing
point. As they dry andthe interfiber distance dcomes to 1 mm, Howmuch contraction stressdevelops between thetwo fibers?

Ionic bond = a chemical bond in which two ions are joined
together because one has a positive charge and the other anegative charge
Covalent bond = a chemical bond in which two atoms share
one or more pairs of electrons that hold them together (ca.
500 kJ/mol)
Hydrogen bond = a weak connection that is formed between
an atom of hydrogen (= a gas) and an atom of anothersubstance such as oxygen or nitrogen (= a gas) （10～40kJ/mol）
Van der Waals forces = the relatively weak attractive forcesthat act on neutral atoms and molecules and that arise
because of the electric polarization induced in each of theparticles by the presence of other particles
Dipolar bond (coordination bond)
Metallic bond

H-O-H

Linear pressure at nip:Thickness decrease ratio, %Gloss improvement and compression of paperd µm
The attractive force iscalled Campbell force.

Biomaterial Science by Toshiharu Enomae

Cellulose surface

Loose hydrogen bond mediated by water

Firm hydrogen bond with a water monolayer Direct hydrogen bond2

May 20, 2014

Inter-fiber bondEvidence of hydrogen bondInter-fiber bondEffect of cell wall thickness on wet fiber flexibility

When paper mass was measured after allowing tostand in deuterium water (D2O) vapor until
saturation, 0.5 to 2.0 % of hydrogen of all thehydroxyl groups was not replaced with deuterium.
This ratio corresponds to the percentage ofhydrogen bonded hydroxyl groups.
Energy required for tensile breakage was calculated.
19 kJ/mol (equivalent to hydrogen bond energy)
Strength decreased with acetylation of carboxylgroupsCell-OH → Cell-O-C-CH3
OInter-fiber bondEffect of fiber flexibility on Relative Bonded Area

Forming (Wire section) － Moisture content
HeadboxSlice

Bonding ratio, %Cell wall thickness, µm
8.8 µm

4.7 µmSize press

Couch rollWiresectionFiber flexibility, 1/Nm2

Pulp
1%
Moiture
99 ％Press
sectionCalendersectionDryer section

20 %

40 %

95 %

80 ％

60 ％

5％

Post-forming－Size press

Post-forming－Size press

SizingPurpose andeffectInternal sizing- addition to pulp slurry
External (surface) sizing – application to surface

What is surface sizing (size press)?
The treatment for providing water-resistant property
to paper by application of starch solution etc.
Other than starch, carboxymethyl cellulose, polyvinyl
alcohol, polyacrylamide etc. are applied. Strong
water-repellency is not required.

Picking prevention
in offset printing
Ink jet printability
to prevent
bleeding

Advantages over internal sizing
100% retained. No deposit on walls of former or froth

Biomaterial Science by Toshiharu Enomae3