June 10, 2014

Biomaterial Science（Schedule）
Date

1

4/15

History of papermaking
Pulps – Beating and fiber properties

ContentBio-Material Science

24/22

35/9, Fri Pulps – Additives and functions

Toshiharu Enomae

45/13

Papermaking processes & interfiber bonding

Professor, PhD, Paper Device and Eco-friendly materials

55/20

Paper– Structural properties

65/27

Paper– Surface properties

76/3

Polysaccharide chemistry by Assoc Prof Akiko Nakagawa

86/10

Paper–Wetting and absorption properties

96/17

Paper– Mechanical and optical properties

106/24

Recent trend of paper science and technology

EG60411

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

Paper structure – Factors affecting density
 Beating and filler loading

Paper structure – Factors affecting density
 Wet press and calendering

0.80.80.7

0.7

Density, g/cm 3

Density g/cm 3#0.6
0.50.4

Beating rev. (PFI mill）

Calcium carbonate addition

Paper structure-Scanning electron microscope(1)

0.6
0.5
0.4

Wet press

Paper structure-Scanning electron microscope(2)100 µmCopy paper

Newspaper

Biomaterial Science by Toshiharu Enomae

Calendering- linear pressure

100 µmJapanese paper

Tissue paper

1June 10, 2014

Paper structure– Smoothness
紙の構造-表面形状測定

Paper structure – Smoothness

Surface profile can be measured in 2D or 3D.
Stylus, light beam, electron beam, or probe Air leak method Air flow rate through a gap between

paper surface and smooth metal plate Surface profile (Microscopy) Surface shape measured using

profilometry such as stylus profilometry,
confocal optical microscope.
 Several ways of expressing surfaceroughness

Oken smoothness, sRa =1 ly dyl ∫0

Root mean squared roughnesszydy

Paper structure –Smoothness of coated paper
450400350300250200150100500

Centerline average roughness(arithmetic average)

RMS =1 l 2y dyl ∫0l

Paper structure - Formation
Formation
[] Unevenness sensed visually when
white light is transmitted through paper – STD or
CV of optical density
Transmitted light I 0  I1 I2 …
log Mass
B1 B2 …
 In 
[]
Distribution oflocal mass Bn –STD or CV ofPaper I0 I0
local mass
Irradiating light
STD=Standard deviation, CV= coefficient of variation

After calendering
Basepaper
Before calendering

05101520

Latex content, pph

Paper structure - Formation
Time until dehydration (s)Transmitted lightimages of softwood
pulp sheets Formation becomes
(F)
worse
by cationicpolymer addition
and increased time
until dehydration
 Cationic polymers
increases fiber
retention.

10Interaction- between paper and water (liquid)

120

Cationic polymer
P:Added
N:Nonadded



Wetting Contact angle
 Surface energy Sizing degree
 Liquid penetration Swelling

HN10HN120

HP10HP120Biomaterial Science by Toshiharu Enomae

2June 10, 2014

Surface chemistry - Contact angleSurface chemistry - Contact angle

Contact angle (θ)
 The angle made by the solid and liquid surfaces

 Supposed that the area including

when a liquid droplet is placed on a solidsurface.
 When 0º< θ < 90º, “wetted” and when θ>90º
γL“unwetted”.

microscopic structure is r times larger
than the apparent one, Wenzel’s contact angleγ

Young equationLθ When the contact angle

is constant, horizontal
components of forces
are balanced.

cosθ w = r cosθγsγiγi － γs ＋ γL cos θ ＝0Surface chemistry - Contact angle On a rough surface,

r=1 の場合

150

r=1.2の場合
r=2 の場合

120

Hardly-wetted

9060

60

90

Wet-press: 90 g/m2, 7.0 kg/cm2

120

150

120
110
100

5000 Rev beating
10000回叩解

90
800030180

真の接触角θ

Beating and smoothness
Oken smoothness, sHardwood kraft pulp sheet Surfacessmoothed bybeating
became easilywetted.

20151050γs

20000回叩解

Easily-wetted

300γiθ130180

見かけの接触角θw

when θw ＜ θ at θ ＜90º, easily-wetted
surfaces become
more easily-wetted.
But, when θw ＞ θ at
θ ＞ 90º, hardlywetted surfaces
become more hardlywetted.

140cos θ w = r cos θWenzel’s equation

θw

Contact angle of paper - Beating effectContact angle, °Contact angle on a rough solid surface

20000 Rev
10000 Rev
5000 Rev

200
400
Contact time, s600

Surface chemistry - Contact angle

On composite surfaces

Cassie's law

 The effective contact angle θC is dependent on

the areal ratio of each component.
 is stated ascosθ C = Q1 cosθ1 + Q2 cos θ 2, where θ1 is the contact
angle for component 1 withareal fraction Q1 and θ2 isθ
the contact angle forcomponent 2 with areal
fraction Q2 (Q1 + Q2 = 1). Component 1 Component 2

Grammage and wet press pressure

Biomaterial Science by Toshiharu Enomae

3June 10, 2014

Surface chemistry - Contact angle

Surface chemistry - Contact angle
Q. What is the contact angle θc of sized paper?
 Sizing agent need not cover the whole surfaceof fibers for repelling water. If a sizing agent
covers 5% of the whole surface, what is thecontact angle θ ?
 Assume that θ is 0˚ for unsized fibers and 120˚for the covering size.
θc(G) × cos 0º +
 cosθc = 0.95
(H) × cos 120º
0.05
Paper
cosθc = 0.95 –(I)0.025 = 0.925(O) ºθc = 92.1

Size(J)θc = 22.3º

Paper
Size

Surface chemistry - Contact angle


Q2. What is the contact angle θc of sized paper?
 Half the volume of paper is air. If 50% ofpaper surface is air, what is the θc ?
 Assume that θc of a true surface of sizedpaper is 22.3˚ and θ of air is 180˚.
(K)(K)
 cosθc = 0.5×cos
22.3º + 0.5×cos
180º(K)(L) + (K)cosθc = 0.5×0.925
0.5× (M)1θc(N)= 0.155

Liquid absorption theory - Capillary model

Comparison in Water absorptionForce developing arounda meniscus of a liquid ina capillary (pipe)
Steady flow in a pipe

γπPr 4Q=8ηlParchmentθ

F=2πrγcosθ
F2πr
S=πr2

θr

l: Capillary lengthr: Capillary radius
η: Liquid viscosity
Q: Volumetric flow rate

Wood-containing paper

P=F/S=2γcosθ/rPγcosθ

(Hagen-Poiseulle equation)“wood-containing” means “made from mechanical pulp”

Liquid absorption theory - Capillary model

Water absorption rate - How to measure

Q. Substitute the relation represented in the figure into
the H-P equation and develop the Lucas-Washburn equation.



H-P equation

2γ cos θrdVdl
Q== π(Q)r2dt
dt
SubstituteπPr 4
Q=8ηl

P=dl

Bristow’s apparatus

A liquid supply head filled witha liquid of volume V scans
paper at various speeds v.

dt2dldV = πr(P)rrγ cos θ ⋅ t2η

Biomaterial Science by Toshiharu Enomae

15 mm (w) Contact time

t=b/v

V
Scan speed
Slid width

Lucas-Washburn equation

l=1 mm (b)Papermovesv

 Transfer Vol

Liquid volume
Slit width
Trace lengthvb

Vt=V/(wL)
Vw
L4