Biermann Ch. Handbook of Pulping and Papermaking

Подождите немного. Документ загружается.

724

ANSWERS TO SELECTED PROBLEMS

13.

Effluents from the later stages, such as a D

stage, can be used to wash pulp at the earlier

stages. Chlorination water can be reused

within the chlorination stage since this stage

does not remove large quantities of lignin

(most of it is removed in the subsequent

alkali extraction stage). Oxygen de-

lignification effluent can be sent to the brown

stock washers.

14.

By allowing the oxygen bleaching effluent to

be used in the brown stock washers, hgnin,

alkali, and water are reused rather than being

sent with the mill effluent discharge.

8. Fiber size distributions can be determined

with a series of screens, by optical scanning

techniques, or by projection.

9. Fiber size distributions indicate what is hap-

pening during mechanical pulping or refin-

ing. Low freeness values are usually caused

by fines generation, but also by fibrillation.

10.

The formation and testing of laboratory

handsheets indicate much about the quality of

the fiber for papermaking. They provide the

papermaker with useful information for trou-

bleshooting if problems develop.

CHAPTER 6

Refining increases the surface area of fibers

to improve fiber—to—fiber bonding. Refin-

ing causes lamination of the fibers to improve

fiber flexibility (and therefore fiber—to—

fiber bonding). Refining also hydrates the

fibers to make them more flexible (e.g.,

compare dry spaghetti to wet spaghetti).

Generally, refining at high consistency in-

creases fiber—to—fiber brushing. This

means less fiber cutting due to refiner

bar—fiber interactions.

Laboratory refining does not duplicate the

conditions of commercial refining; therefore,

it is not a perfect comparison of how fibers

will actually behave in the commercial pro-

cess.

The level of refining is usually determined by

the freeness of the pulp. Other methods such

as the size distribution of the fibers can be

used as well. Handsheet testing is a good

indicator of the effectiveness of refining.

At elevated pH the carboxylic acids are no

longer in the acid form, but in the salt form.

In this form refining is more effective be-

cause the fibers are hydrated more easily.

The paper strength properties are improved

because the fibers are more flexible. This is

especially true when the salt form is with

sodium ions. (Hard water in a mill would

hinder the process at pH above 7 or so.)

CHAPTER 7

The moisture content of paper (and its

strength properties) under standard conditions

depends upon whether the paper loses or

gains water. Therefore, TAPPI standards

state that paper should be placed in a hot, dry

room before conditioning to standard condi-

tions.

The paper may be over dried or under dried

relative to the moisture content it will achieve

under standard atmospheric conditions. It

may take well over an hour for paper to

achieve its equilibrium moisture content.

Also,

see question 2.

The fold test is extremely sensitive to the

moisture content of the paper. For example,

consider how the moisture content of spa-

ghetti influences how easily it is bent without

breaking. The analogy is fair since both

spaghetti and cellulose fibers have

polysaccharides of similar structures.

Fiber alignment is usually credited with this

phenomenon, but the fact that paper is dried

under tension in the machine direction, but

not in the cross machine direction, accounts

for much of this effect. Individual fibers

dried under tension are stronger and stiffer

than fibers not dried under tension.

8. In this case, the basis weight is an average

over an area of 144 in.^ In the case of the

fold endurance test, an area of about 15 mm

by 1-2 mm is tested, or up to 30 mm^ is

CHAPTER 7 725

tested. Small imperfections in formation

would not be noticed in the first case, but

could be most of the test area in the second

case.

(This is related to the concept of statis-

tical sample size where variability is inverse-

ly proportional to the square root of sample

numbers.)

9. Scanning electron microscopy with X—ray

analysis and atomic absorption spectroscopy.

10.

Paper brightness is the relative amount of

reflected light at 457 nm.

11.

The two commonly used tests are the G.E.

brightness and Elrepho brightness, which

differ in the geometry of the light source and

light detection.

12.

All of these, except increased refining, will

increase the opacity.

CHAPTER 8

Pressure screens and vortex cleaners.

Control additives are not designed to become

an integral part of the paper. They are used

to improve the papermaking process. Func-

tional additives are used to become an inte-

gral part of the paper and influence the

properties of the paper

itself.

PCC generally costs less than wood fiber and

can save money. PCC also improves the

opacity and brightness of the resulting paper.

Titanium dioxide is used since it has a high

index of refraction and brightness.

1. Allows use of CaCOs as a filler, which

would otherwise decompose at pH

below 7 by the reaction:

CaCOj^-

+ 2 H^ -> CO2 t + H2O

Less corrosion of the paper machine.

Increased longevity of paper due to de-

creased acid-catalyzed hydrolysis of

cellulose and hemicellulose.

Paper has higher strength since the

fibers are more flexible at higher pH.

Allows the use of secondary fiber con-

taining CaCOs filler.

6. Clay fillers.

Since strength is the most important feature

of this paper, fillers are not used.

8. 1. The viscosity and polarity (surface ten-

sion) of the liquid. In the case of rosin

sizing, the coordinating potential of any

ligand in the liquid is important.

Base sheet properties (bulky, porous

sheets pull in more water by capillary

action than dense sheets).

The contact angle of the liquid on the

surface. (If the angle is less than 90°,

we say it is unsized.) This is a function

of (2) and the polarity of the surface,

such as whether or not hydrophobic

groups (from internal sizing) are on the

surface of the paper.

9. One does not normally size these papers

since they are designed to be absorbent.

10.

Both of these are similar in that they have a

hydrophobic (water-hating or nonpolar) por-

tion which resists water and a functional

group that ultimately bonds with the fiber

surface. The main difference is the mecha-

nism of

bonding.

With rosin, aluminum ions

complex with rosin and the fiber surface to

achieve bonding, whereas with the synthetic

size agents, covalent ester linkages are

formed. The latter group, while expensive,

are much more effective in that much lower

quantities are required.

11.

Rosin size is most effectively used under

acidic to neutral conditions. PCC has a pH

of about 8, which makes it difficult to use

with rosin sizing.

13.

Starch; the bond between glucose units is a

instead of the jS linkage occurring in cellu-

lose.

The mechanism of adhesion is hydro-

gen bonding. In this regard, starch is similar

to hemicellulose in increasing the strength of

paper.

CHAPTER 9

An object in motion tends to remain in mo-

tion in the same direction. When the web

726 ANSWERS TO SELECTED PROBLEMS

goes through a curve the water tends to go

straight (an example of centrifugal force),

away from the web. An S—shaped curve

allows this effect to occur on both sides of

the web consecutively.

The large fibers make an excellent filter mat

next to the screen; this allows smaller parti-

cles to be trapped that might otherwise es-

cape through the screen. The sweetener

stock is recovered along with the fines.

Small—scale turbulence (microturbulence) is

desired and necessary to keep fibers sus-

pended in the pulp slurry and well dispersed.

Large—scale turbulence (macroturbulence

and splashing) is not desired since this will

lead to large amounts of fiber in some areas

and little fibers in other areas. This would

have a disruptive effect on paper formation.

Paper leaves the press section at higher con-

sistencies using less energy in the dryer sec-

tion. The higher consolidation of the web

gives better fiber-fiber bonding leading to a

stronger paper.

To prevent rewetting—the tendency of the

water from the felt to rewet the web when

the pressure is released.

6. Pressure is applied at the ends of press rolls.

The press rolls are made slightly larger in

diameter in the middle (perhaps 0.05 in.) so

that the pressure is evenly dispersed across

the width of the paper machine.

No, rather they tend to get plugged with

fillers, pitch, and other debris. Calcium and

aluminum ions may help precipitate materi-

als,

so felt washing solutions often have a

chelating agent added to them.

8. Pitch from wood, polymers from secondary

fiber, and additives used in the mill such as

defoamers and sizing agents. Again alumi-

num and calcium ions may help precipitate

these materials. Also, the felts collapse and

the void volume decreases.

9. This increases pressing efficiency. Heating

water lowers its viscosity and increases its

rate of removal while pressing.

10.

Tissue paper is too weak to withstand the

numerous felt transfers of conventional dry-

ers.

11.

Tissue paper, see the answer immediately

above, and writing papers with a machine

glaze (the surface of

the

paper in contact with

the dryer gets a smooth sheen on it).

12.

The earlier dryer sections are relatively cool

to prevent a large amount of steaming that

would cause blisters in the paper, while the

later sections are much hotter to drive off the

chemisorbed water.

13.

A coarse dryer felt will allow faster water

removal, but a fine dryer felt leaves fewer

impressions on the sheet.

14.

Typically it takes

1.2-1.6

lb of steam to re-

move 1 lb of water from the paper in the

dryer section. In multiple effect evaporators

with a steam economy of 5, 0.2 lb of steam

removes 1 lb of water from the black liquor.

15.

Pigments and binders.

16.

The refining stage offers the most control

over the final caliper of paper. Glassine, a

very dense paper, is made with much refin-

ing. Calendering is used to control the

caliper across the sheet for uniform winding.

Pressing has an appreciable influence on the

final sheet caliper. Refining (most impor-

tant),

pressing (moderately important), and

calendaring (relatively unimportant) all in-

crease the density of paper.

17.

Small particles such as fines and fillers are

washed out of the wire side, hence the ash

content (fillers contribute to ash since they

are inert and not combustible) is higher on

the felt side. This contributes to two—

sidedness of paper.

18.

Two—sided paper tends to curl since one side

might absorb water slower than the other side

or water might have more of an effect on one

side than on the other.

A thermostat coil is a bimetallic strip of

metal. One side of the strip is one type of

metal and the other side of the strip is a

CHAPTER

727

metal with a much different coefficient of

thermal expansion; therefore, a change in

temperature causes a curling effect. (With

paper, a change in moisture content is more

important than a change in temperature.)

19.

Strength is desired for obvious reasons, such

as to prevent breaks in the web in the print-

ing press. Bulk is desired because it contrib-

utes to opacity. (The more air in the sheet,

the more fiber-air interfaces that scatter

light.) Unfortunately, the bulkier the sheet

the lower is its strength (that is, there is an

inverse relationship). As in life, most things

in pulp and paper are a compromise.

20.

Wet strength adhesives often form covalent

linkages. Most papers, however, are held

together by hydrogen bonding without the use

of added adhesives. Starch is often added to

paper with a concomitant increase in the dry

strength due to hydrogen bonding. Hemi-

celluloses have a similar effect.

21.

A corrugated box is like an I—beam. The

center of the beam only separates the top and

bottom, where the forces are highest. Con-

sider a 2 by 4 piece of wood laying flat

supported on each end by a cement block.

When

one

jumps in the middle, it flexes quite

a bit. When put on the narrow side, flexing

decreases substantially because this beam is

now "thicker".

22.

Starch is a hydrophilic molecule; its mecha-

nism for imparting sizing to paper is much

different from that of rosin or the alkaline

sizing agents. Starch acts to "plug" the

capillaries on the paper surface, thereby

decreasing the rate of water penetration.

CHAPTER 10

A high efficiency can be achieved with high

fiber reject rates, but much useful fiber is

lost.

Flotation and washing. Some processes use

both methods.

Sodium hypochlorite would tend to react with

all of the lignin (of the large amount present)

and not just the chromophores.

6. Originally these were centrifiigal cleaners

"operated in reverse" that removed light-

weight materials through the top, where

fibers usually exit. Both the contaminants

and the fibers leave through the bottom in

through—flow cleaner. Through—flow

cleaners are used in secondary fiber plants to

remove plastics, styrofoam, and other materi-

als less dense than wood fibers

CHAPTER 11

Material that is suspended (not dissolved) in

the water.

BOD, color, suspended solids, and other

materials such as acids or bases.

Color.

Both oxygen and carbon dioxide have lower

solubilities in water at high temperatures.

The limited solubility of oxygen in the warm

summer months (along with lower water flow

rates in rivers) often means that the allowable

BOD discharge rate is lower.

Lower oxygen solubility in the water and

decreased flow rates.

6. This is not easily removed and requires the

tertiary water treatments. It is seldom prac-

ticed commercially.

The biological oxygen demand test must be

carried out with microorganisms in order to

simulate the fate of organic materials in

rivers or lakes. Microorganisms take several

days to metabolize the available food, espe-

cially mill effluents, which contain many

materials that are difficult to metabolize.

8. One gallon is about 3.78 kg (or liters) so

75.6 X 10^ kg effluent is produced daily and

27.6 X 10^ kg is produced annually. This is

equal to 27.6 X 10^^ g annually or 27.6 x

10^^

mg effluent annually. Since 10 parts

dioxin per quadrillion part effluent are pro-

duced, less than 300 mg of dioxin is pro-

duced each year.

9. HjS and CH3SH can both be removed by

alkali scrubbing as they have an ionizable

728 ANSWERS TO SELECTED PROBLEMS

proton, that is, they are weak acids. By

reaction with a metal hydroxide, a salt of low

volatility is produced.

RSH + NaOH ^ (RS" + Na+) + H2O

10.

The reactions of sulfides with the methoxy

groups of

lignin.

It is an undesirable product

since it is highly odorous and not easily

trapped.

11.

Nitrogen oxides form during any high—tem-

perature combustion process where nitrogen

from air can react with excess oxygen. Ex-

cess oxygen must be present or carbon mon-

oxide emissions would be very high.

12.

Ambient sampling is done in air in the vicini-

ty of a mill. Point sampling is done directly

at the source (such as the smokestack) of gas-

eous effluents.

13.

Some pollutants are formed under reduction

conditions (CO and TRS) while others are

formed under oxidation conditions (SO2 and

NO^),

so there is always a tradeoff between

levels of these pollutants.

CHAPTER 12

The following shows that a ream which

weighs 52.3 pounds means the paper has a

basis weight of 85 g/m^.

1 lb 1 ream

ream x 24in. x 36

in.

500 sheets

, 454g ^ (39.37in.)^

^ ,, .

lib (Im)^

This cannot be done since the units are in-

compatible.

CHAPTER 13

d) All of the above.

c) Na^S.

a, c, f, g, i,

6. c, since hydrogen bonding occurs.

a) 0.546 mole.

b) 0.0537 mole.

c) 2.69 mole.

8. d) 50%.

9. 30.1 gC02.

10.

0.74 M.

11.

35 g of NaOH; 437.5 mL as (875 mL of 0.5

12.

a) 1.33 is the pH.

b) 1.70 is the pH since there are two ioniz-

able protons in sulfuric acid.

c) 11.1 is the pH.

15.

Cr is +6.

16.

Na loses an electron, is itself oxidized, and is

the reducing agent since it causes water to be

reduced.

17.

One lb of NaOH is 11.3 moles of Na. Since

each sodium atom requires one electron, this

is 96,500 amp seconds (the number of elec-

trons in a mole) times 11.3 or 303 amp

hours.

At 4 volts this is 1214 watt hours or

1.214 kWh, but this is the ideal minimum.

18.

Corrosion occurs at a small point made the

anode with a high surface area cathode, so

the reaction is intense at a small point.

19.

If the magnesium strip is used up, then cor-

rosion can occur to the water heater

itself.

The high temperature and hot water can

make corrosion very quick. This is a perfect

example of "an ounce of prevention being

worth a pound of cure."

21.

C^H,^.

CHAPTER 14

The normality of the diluted NaOH = (21.37

mL X 0.1027AO/20.0mL = 0.1097iV. The

normality of the concentrated NaOH =

0.1097 A^ X (1000/25) = 4.39 A^ NaOH.

The concentration of the NaOH = 4.39 N

NaOH X 40 g/eq = 175.6 g/L.

The amount of water present during the titra-

CHAPTER

729

tion is not critical as long as there is not

undue dilution; it does not enter into the

calculations above; however, it is important

to know the precise dilution factor as this

does enter into the calculations.

Use of Eq. 14-2 gives with p^^ of 4.76 for

acetic acid gives:

pH = 4.76 + log (0.2/0.5) = 4.36

a, c, d.

No, not without large dilution factors.

6. Just like pH indicators such as phenolphtha-

lein, the bleach effluent contains compounds

whose colors are very pH dependent. Mea-

suring the color at a low pH would underes-

timate its true color in the environment.

The following reaction shows the liberation

of acid that could cause acid hydrolysis of

cellulose and hemicellulose over a long

period of time.

(n-2)+

+ 2H"'

CHAPTER 15

Lumber: 150,000 x (1.5 x 3.5)/(2.0 X 4.0)

= 98,437 true board feet

98,437 true board feet x (1 ft^)/(12 bd ft) =

8203 ft^ lumber

8203 ft^ lumber x (62.4 Ib/ft^ x 0.44) =

225,225 lb oven—dry wood as lumber

225,225 lb lumber x (2000 lb/ton) = 112.6

tons oven—dry wood; 112.6 tons dry lumber

X (1.20 4- 1.0) = 247.7 tons wet lumber

Chips: 112.6 tons dry wood x (33.3

chips/50 lumber) = 75.1 tons dry chips (62.5

BDU)

„^

,, 2000 lb

75.1 tonx X.

ft^

V IRJlcar ^^,^

Iton lOlbchips 18x200ft^

75.1 tons dry chips x (1.2 + 1.0) = 165.2

tons wet chips

Weight/car: 165.2 wet tons/4.17 cars =

39.6 tons

Sawdust: 112.6 tons dry x (16.6/50) =

37.53 tons dry; (31.3 BDU or 82.57 wet

tons)

Rail cars: 2.61 RR cars; 39.6 tons/car

Revenue: 62.5 BDU x $160/BDU + 31.3

BDU X $60/BDU = $11,878

1 m^ of water weighs 1000 kg (1 metric ton)

and 1

ft^

of water weighs 62.4 lb, oven—dry

weight: 1000 kg/m^ x 0.42 = 420 kg/m^

62.4 Ib/ft^ X 0.42 = 26.2 Ib/ft^

green weight: 420 wood X (100 kg green/55

kg dry) = 763 kg/m^; 26.2 wood x (100 lb

green/55 lb dry) = 47.6 Ib/ft^

weight of water: 763 green — 420

oven—dry = 343 kg water/m^; 53.7 green

— 26.2 oven—dry = 27.5 lb water/ft^

Weight of dry wood/ft^: 62.4 x 0.45 =

28.1 Ib/ft^

Green weight: 28.1 Ib/ft^ x (1/(1 — 0.45))

= 51.1 Ib/ft^

Oven—dry weight/m^: 1000 x 0.45 = 450

kg/m^

Green weight: 450 kg/m^ x (1/(1 — 0.45))

= 818 kg/m'

Vol. of chips: (28.1 Ib/ft^ wood)/(10 Ib/ft^)

= 2.81 ft^ chips/ft^ wood; and the same

applies to give: 2.81 m^ chips/m^ wood

Use of

Eq.

15-8 shows the breaking length is

2.48 km, which is weaker than most types of

paper.

730 ANSWERS

SELECTED PROBLEMS

J50LP?i

=2.48 km

,-1

0.85

1422psi-km"

CHAPTER 16

3a. liquor sulfidity = 37.5% = Na2S/AA; since

y2Na2S = (AA - EA), 37.5% = 2 x (AA

- EA)/AA X 100%; AA = 115.3 g/L as

Na20.

NaOH = (2 X EA) - AA = 72.1 g/L.

Na2C03 = 20.45 g/L as Na20; TA = 135.8

g/L.

1.017 N HCl = 31.53 mg NajO/mL titrant.

10 mL liquor = 10 mL x 93.7 mg/mL EA

= 937 mg EA/aliquot; therefore, Titration

"A"

is 937 mg/(31.53 mg Na20/mL titrant)

= 29.72 mL titrant; B = 36.57 mL; C =

43.07 mL.

3b.

Mol/L of NaOH = (2A - B) mL x 1.017

MIO mL = 2.32 M.

Na2S = NaHS = (B - A) mL x 1.017

MIO mL = 0.697 M. Na2C03 = 0.66 M.

3c.

There is 100 g dry wood. EA = 93.7 g/L

X 0.2 L/(100 g wood) X 100% = 18.7%

EA on wood.

600/hr X 1.43 hr = 858

858/(910/hr) = 0.94 hr

It is a molar comparison.

6. Combined is 3%. Sulfurous acid is 1%,

bisulfite is 6 %, and sulfite is 0 %. (Apprecia-

ble amounts of both sulfurous acid and sulfite

ion cannot exist in solution simultaneously.)

By difference, the free SO2 is 6%. To get

the concentration of each of the species we

realize by the strong equilibrium shift to the

right in the equation below that both sulfu-

rous acid and sulfite ion do not exist in

solution together (in any significant concen-

tration). Therefore we have to "remove" at

least one of the species. Thus 2% sulfite ion

(combined form, leaving 0% sulfite ion) and

sulftirous acid (free form, leaving 4%

sulfurous acid) react to give 4% bisulfite ion.

According to Fig. 16-8, the pH will be about

2 since we have a ratio of 50% of the sulfu-

rous acid species and 50% of the bisulfite

species.

SO32-

+ H2SO3 -^ 2HSO3-

+ 2% -^ 4%

9. lodometric titration gives free SO2 (10%),

and titration with NaOH gives free SO2

(6.5%),

leaving 3.5% SO2 as combined.

3.5%

free reacts with 3.5% combined to give

bisulfite and 3% sulfurous acid as the

actual chemical present on a SO2 basis.

CHAPTER 17

CIO2 has five electrons transferred per CI

atom, while CI2 has one electron transferred

per CI atom. Therefore, ClOj gives much

more bleaching power for the chlorine con-

tent. Furthermore, CIO2 reacts principally by

oxidation with most of

the

chlorine ending up

as harmless, inorganic CI". On the other

hand, CI2 reacts principally by substitution of

chlorine for hydrogen in the organic com-

pounds. The resultant chlorinated organic

compounds increase the toxicity of effluents.

(Chlorinated organic chemicals include DDT,

dioxins, PCBs, herbicides such as 2,4-D and

2,4,5-T.)

NaOCl + H2O +

21-

+ NaCl + 20H-

[CIO2] = 0.0606 Nhy Eq. 14-1. Table 17-2

shows this is 0.819 g/L.

100%

—

(0.16% lignin/kappa x 34 kappa +

2%) = 92.6%. If the original pulp yield is

46%,

the overall yield of bleached pulp is

0.926 X 46% =42.6%.

6. Five gallons is about 24 L. (When using

large portions of water like this, it is more

accurate and faster to weigh it rather than try

to measure its volume. Also, start with 23.5

L so that it can be diluted to the exact vol-

ume that corresponds to 0.1000 N,) The

equivalent weight of potassium permanganate

CHAPTER 17 731

is one—fifth the formula weight or 158/5 =

3L6.

Weigh 31.6 g/eq X 24 L X 0.1 eq/L

= 75.84 g of KMn04 and add it to the wa-

ter. (Freshly distilled or boiled water should

be used.) Add 100 mL of water, 25 mL of

2 M H2SO4, and 5 mL of 2 M KI (using

graduated cylmders) to a 250 mL Erlenmeyer

flask. Pipet 25.00 mL of the KMn04 solu-

tion into the flask. Titrate the liberated

iodine with thiosulfate until the blue color of

the starch indicator disappears. Repeat the

titration. Calculate the concentration of

KMn04 and dilute to give 0.1000 K Check

the concentration with additional titrations.

8. The height of water is 20.4 meters; volumet-

ric flow = 2.0 mVsec.

The slice height is 0.01 m = 1 cm. The

production is: 20 m/sec x 10 m x 50 g/w?

X 1 kg/1000 g = 10 kg/sec.

10 kg/sec X 60 sec/min x 60 min/hr x 24

hr/day x 365 day/year x 1 MT/1000 kg =

315,360 MT/year = 347,000 tons/year.

CHAPTER 18

There is a series of small void spaces or

tunnels that small compounds can enter but

large ones cannot. The apparent volume for

small molecules is much higher than that for

large molecules; hence, for a series of simi-

lar molecules, the small molecules are eluted

(come off the column) last—a characteristic

unique to gel permeation chromatography.

DP„ = 300; DP^ =

333.3.

Since the sty-

rene monomer has a mass of 104, the num-

ber average molecular weight is 104 x 300

= 31,200.

Anionic polymerization.

CHAPTER 19

Sodium borohydride reduces the end group of

cellulose (or hemicellulose) that contains the

free anomeric carbon (that is, the free alde-

hyde group, the reducing end). This is the

same end from which the peeling reaction

occurs. The reducing end is converted from

an aldehyde to an alcohol which does not

undergo peeling in alkaline solution.

The cellulose viscosity of mechanical pulps is

generally very high and not a limiting factor

in the strength properties of these pulps.

There has not been any severe treatment

during the processing of these pulps that

would lower the degree of polymerization of

the cellulose.

CHAPTER 20

95.45% lie within ±2 standard deviations.

99.73%

lie within ±3 standard deviations.

99.994% lie within ±4 standard deviations.

CHAPTER 21

Soap forms micelles which have non polar

centers that can dissolve oil or grease so that

an emulsion is formed.

No.

Blue light is scattered to a much higher

degree than other colors. We see the scat-

tered blue light in the sky.

CHAPTER 22

CTMP pulp produced with sulfite is probably

sulfonated; these groups will affect the

surface charge of the pulp.

Quaternary ammonium groups.

They have a higher surface area.

One of the polymers is of high molecular

weight and, therefore, shear sensitive.

CHAPTER 23

Offset printing uses an intermediate blanket

to transfer the ink from the plate to the

paper. It refers to lithographic printing.

Halftone printing allows shades of gray to be

reproduced using a grid of dots so that any

point on the paper is either black or white.

It is used for reproduction of photographs.

Stochastic printing uses a computer—gener-

ated "random" dot placement. It gives high-

732 ANSWERS TO SELECTED PROBLEMS

er resolution and avoids moire patterns. The

latter advantage is especially important in

multicolor printing.

Four—color printing uses four colors of ink,

which allows reproduction of a wide variety

of hues at various levels of saturation. It

uses subtractive mixing of color inks, where

each ink (ideally) selectively removes one of

the additive primaries. In other words, each

ink transmits (reflects) two of the additive

primaries and absorbs one of the additive

primaries. The additive primaries are the

three colors that respectively selectively

stimulate the three types of cones in the

human eye.

6. Proper color reproduction is possible only if

each of the four inks is printing at the proper

intensity (as checked by a densitometer).

Gravure and letterpress put much less stress

on the coating adhesive than offset, so paper

made for gravure will probably give picking

problems when used for offset.

CHAPTER 24

Optical brighteners absorb light in the ultravi-

olet range and give off light in the visible

range. The effect is identical to that used in

black light paints to produce posters and, in

a sense, makes the object "brighter than

bright," by giving off more visible light than

shines on them, if

the

light source has signifi-

cant amounts of UV light.

Yellowish paper absorbs more blue light than

yellow light and does not appear to the hu-

man eye to be bright. By adding blue dye

the paper, the amount of yellow light ab-

sorbed is increased to "balance" the light

coming off. While such paper actually

reflects less light, it appears to be brighter.

The way the eye and brain perceive the color

of an object depends very much on the

source of light. This is exemplified by

observing objects under sodium-vapor lights

such as yellow street lights, or, less directly,

by taking pictures with the same type of film

with no filters, using different sources of

light such as incandescent, fluorescent, or

sunlight.

Red, orange, and perhaps some yellow de-

pending on the source of the color; blue

alone if a high-quality filter is used or if it

light from a laser; black; green, since this

color is not absorbed efficiently, but largely

reflected, there is no way for the plant to

trap its energy.

6. Blackbody radiation at higher temperature

tends to flatten the spectral distribution of the

light source and is a more efficient light

source.

The new paint had a slightly higher gloss.

This is one problem with "computer paint

matches," but I feel the match will improve

as the new paint weathers and loses some of

its gloss.

8. Opacity is improved since light is scattered to

a higher degree.

9. Light scattering decreases with particle size

below 50% of the wavelength of the light

involved. Is this true of light absorption?

Try to think of an example in order to come

to a conclusion.

10.

Using Eq. 24-8 or a table gives k/s as

0.0100 and 0.00132 for 0.87 and 0.95,

respectively. Therefore, k is 0.0005 and

0.000066 for 0.87 and 0.95 absolute bright-

ness,

respectively, a very large change in k\

11.

Since ^W^is 2.0 and R^ is 0.87, the Tappi

opacity, Q.gg, is read as 0.74 from Fig. 24-

16.

12.

Refining leads to a sheet of higher density

(better fiber—fiber conformation) so that

there is less air—fiber interface to scatter

light. This effect is more important than the

relatively minor increase in surface area of

the pulp.

CHAPTER 25

No.

Hardwoods.

AUTHOR

INDEX^

3M, 162, 183, 184

Adams, 499

Adler, E., 701

Aflenzer,

F.A.,

506,510

Ahlers, P.-E., 708

Ainsworth, J., xi, 1, 24, 26, 104,

112,

126, 130, 366

Ainsworth, SJ., 688, 697

Akhtar, M., 706

Alander,

P., 127, 134

Alexander,

A.E., 423, 436

Allen, L.H., 207

Alsholm, H., 120

Althouse, E.B., 135

Amsden, CD., 295

Anders, J.E., Sr., 660

Anderson, N.A., 648, 670

Anderson, W.A., 121

Andritz

Sprout-Bauer,

Inc., xv,

xvi, 78, 144446, 152, 293

Angeus, L., 718

Anon., 534, 539, 636, 639, 652,

654,

660, 689, 694, 697

Aronovsky,

S.L, 636, 637, 639,

640

Arrhenius, S., 368, 370

Aspler, J.S., 188

Asplund, 60, 69, 70

Atchison, J.E., 53, 633, 640

Attridge, M.C., 706

Attwood, 448

Avery,

L.P., 718

Awerin, A., 461

Ayton, J., 135

Aziz, S., 99

Babcock

and Wilcox, 94, 107-109,

111

Bach, E.L., 261

Backa, S., 718

Backman, R., 709

Bacon, F.C., Jr., ix

Baekland, 395

Baeuerlin, C.R., 709

Bafile, P., 52

Bailer, m, J.C., 295

Bailey,

J.H.E., 702

Bain, R., 53

Baker, D.E., 259

Ballard, J., 260

Balos, B., 281

Bamber,

R.K., 540, 581

Banerjee, S., 713

Bares, S.J., 188

Barham, D., 118,

121,709

Barker, N.J., 720

Batelka,

J.J., 188

Battan, G.L.,

458,459

Bauer

Bros., 67

Bauer, D.G., 121

Bauer, J.V., 673

Bauer-McNett,

151, 152, 439,

454,

705

Beach, M., 470,481,483,484,

486

Beck,

D.A., 260

Beer's

law (spectroscopy), 342

Bekk (paper

surface), 170, 171

BeloitCorp., xvi, 90, 187, 212,

227,230,231,237-239,270,

271,

274, 275, 281

Berben, S.A., 718

Berg,J.C.,

428,431,436,704

Berg, J.M., 436

Bergh, P.A., 419

Bergstrom, R.E., 707

Berlyn, G.P., 539

Berlyn, R.W., 24, 52

Berndt,

G., 709

Bernoulli,

648, 657, 668

Berol,

705

Berry,

R.M.,

295,708

Besley,

534

Betz, 680, 684

Bevan, E.J., 395

Bichard, W., 392, 393

Biermann, C.J., 11,99,206,208,

346, 347, 385, 393, 439, 441,

446,449,450,451,452,459,

460, 462, 509, 512, 702, 719

Billmeyer,

F.W. Jr., 508

Bills, A.M., 135

Biv,

RoyG.,

489,512

Black

Clawson, xi, xvi, 193, 230-

232,235,238,240,251,252,

266-271,

273, 280

Black,

N.P., 99

Blackwell,

B., 121

Blanchette, R.A., 706

Blasche, D.W.,

467,483

Bliss,!.,

271,281

Bobalek,

J.F., 704

Bolam, F., 711

Bolker,H.I.,

377,710

Boltzmann, 425, 500

Bonano, E.J., 393, 700

Bormett,

D.W., 676

Born, 426

Bostwick,

J.H., 135

Bourdon, 667

Bowen, L.J., 279

Brandenberger,

J.E., 395

Brautigam, G., 713

Bray,

M.W. 706

Brazier,

J.D.,

531,537

Brimmer,

P.J., 718

Brink,

K.L., 648, 660

Bristow,

J.A., 173, 188

Britt,

K.W., 9, 151, 154,439,

444,

445, 446, 454, 456, 460

Brolin, A., 718

Br0nsted, L., 318, 343

Brown, CM., 282

Brown, H.P.,

526,538,541,552

Brown, R.B., 153, 155

Brown, W.F., 120

Browning,

B.L., 188, 701

Browning,

J., 654

Brunner,

CC, 496, 500, 509

Bublitz, W.J., xi, 4, 230, 234,

236, 244, 712

Buchanan, E.R., 660

Buckman, 705

Burgess, 86

Burkett,

K., 98

Burkhard, G.,

217,258

Burley,

J.,

540,581

Burns, D.A., 718

Burris, B., 120

Burton, D., 120

Busayasakul,

N., 717

Busker, L.H., 260

Butler, D.A., 509

Byrd, Jr., M.V., 710

Byrd, V.L., 156

Calderon, P., 145, 146, 155

Campbell,

A.G., xi, 702

^Most proper names

are

included

here,

including equipment

and

process

names.

733