Chemistry of Papermaking

References: Pulp Technology and Treatment for Paper, 2nd edition James d'A Clark, Miller Freeman Publications, Inc. San Francisco, 1985

"The more one knows about the fundamental nature of a material or a process, the more likely it is that some improvement can be effected." James d'A Clark. Title page.

"Basically the pulp and paper industry is concerned with taking vegetable matter apart, then bonding selected portions with the aid of water. Thus it is important to have some concepts of the nature of cellulose, water, and other materials, and of the forces that apply to the constituent parts. Éweaker and non chemical bonds between particlesÉ are so important with respect to paper." James d'A Clark. page 14

Atoms, Molecules, Ions, Periodic Table

Study of chemistry deals with electrons and what they are doing

Bonding, of whatever type, involves attractions between +/- . (repulsions -/- and +/+

Modern view of atom

Protons, electrons, neutrons, atoms

Atomic number, Z, is number of protons

BLB: (2.1, 2.2) 2.3

HP: 2.2, 2.3, 7.3,

JJ atom structure

CO atom

NEO(protons...)

NEO atom structure

P (Just through Practice Problem #1)

Nuclear Symbols includes practice

Molecules and ions

Molecules - chemical bonds, covalent bonds, sharing electrons.

Chemical properties of atom depend on the number of electrons in the outer orbits/shells.

Complete orbits/shells stable - 2 or 8 electrons.

Models, structural formulas

Ions

Positive ions - cations (move to cathode in electrolytic cell)

Negative ions - anions (move to anode in electrolytic cell)

Ionic bonds - attraction of oppositely charged ions

e.g. Na+, Cl- go to form NaCl, but not a diatomic molecule, rather a network of ions with ratio of 1 Na+ to 1 Cl-

BLB: 2.5, 2.6

HP: 2.6, 2.7, 2.9,

JJ bonding

CG ionic

CC (Intramolecular bonds only at the moment)

CT ionic

CT continuum

NEO molecules and ions

Periodic Table

Metals, nonmetals

Vertical columns

Groups, families.

Similar chemical properties since same outer electron structure

Valence - number of electrons away from an inert gas structure

Measure of capacity, NOT ability of substance to join with other ions or elements to form compounds

Valence electrons are the outer electrons

Inner electrons are called the core electrons

Nucleus with inner electrons called the core

Horizontal rows

Periods

Same shell/subshell being filled

Aufbau, electron configurations

BLB: 2.4, (6.5), 6.6, (6.7), 6.8, 6.9

HP: 2.5, 7.9, 8.2, 8.3, 8.4, 8.5, 8.8

JJ periodic table

CC periodic table

CC Quantum numbers (includes a worksheet with answers)

CC electron configurations (the worksheet, scroll down!)

CT

CT

P (this has 10 sections - most are appropriate. There are practice problems with answers)

P (and choose Valence Electrons, some practice)

NEO Per Tab trends

TQ (Be sure to click on the Mission button and try the exercise)

Chemical Bonds

Properties of bonds include

Bond energy - the energy required to break a bond

Bond length - the distance between bonded species

Bond angle - takes three atoms to form an angle!

Ionic and covalent bonds, again

BLB: (8.9)

HP: 9.10

Electronegativity

The ability of an atom in a molecule to attract toward itself the electrons it is sharing

Imagine a big arrow on the periodic table running from the lower left corner toward the upper right corner.Electronegativity increases as you move along the arrow

Difference in electronegativity of two species useful in predicting types of bonds

0 -> covalent, (almost) even sharing of electrons

Intermediate -> polar covalent

Large -> Ionic

Éand all shades in between

BLB: 8.5, 8.6

HP: 9.7

CG electronegativity

P (and choose Electronegativity)

Bond polarity

Unsymmetrical distribution of electrons leads to polarity

Dipole moment - a measurable property

Remember we are talking about distribution in 3 dimensions

BLB: 8.5

HP: 10.2

P Polarity

Ions: electron configurations and sizes

Inert gas structure achieved in covalent bonds and by ions in ionic bonding

Sizes of ions

Basic idea is protons in nucleus pulling in on electrons

In isoelectronic species (iso = same), larger ion has smaller Z

BLB: 8.2, 8.3

HP: 8.7

Covalent bond

e.g., H₂, Cl₂, H₂O, CH₄, NH₃

Much stronger bond than ionic bond

Balance between sharing of electrons and repulsion of positive nuclei

C bonds with other elements form tetrahedron

BLB: 8.4, 8.6

HP: 2.9, 2.10, 25.3, 25.5

CG covalent

P (choose Covalent bonds)

CG simple C compounds

TQ (simple compounds)

Bond energies and bond lengths

Bond energy is energy needed to break the bond, therefore larger bond energy means stronger bond

Other things being equal, stronger bond -> shorter bond.See Bond length table

BLB: (8.9)

HP: 9.10

Localized electron model

Lewis structures

Method for showing bonding involving valence electrons

Ions, atoms, molecule

BLB: 8.1, 8.4

HP: 9.1, 9.2, 9.6, 9.8

CC Lewis practice

CC more Lewis practice

CT Lewis

Other Bonds

Structure and Bonding in Metals

Regular array of atomic cores in a 'sea' of valence electrons

Intermolecular forces - Physical bonds

Properties

Attractive forces between molecules

Polar attractions - dipole-dipole interactions

Fairly weak, compared to chemical bonds

Strong enough to cause gases to liquefy or solidify, raise melting and boiling points

Examples

van der Waals forces/London forces - weakest of all bonds

Polarizability - larger cloud easier to distort/polarize

BLB: 11.2 (395-398)

HP: 11.5 and intro (476-480)

Hydrogen bonds

Always involve H

But H must be attached to N, O, or F

And there must be a N, O, or F with an electron pair to share.

Water, H₂O, is a particularly famous example

BLB: 11.2 (399-403)

HP: 11.6 (481-485)

CG H bonds

C&A Science for Handpapermakers Vol I

C&A The Role of water in papermaking: H bonds

Organic and Biochemistry

Alkanes

All bonds between C atoms are single bonds

All of the other intermolecular bonds to C are to H

P (Choose Alkanes)

CC (Scroll to Organic and Biochemistry sections. Lots of links which I haven't looked at. If you do, let me know which are good. 1-30-01)

TQ Alkanes

Alcohols

A C-H bond becomes a C-OH bond (the H is bonded to the O)

The -OH group is polar

BLB: 25.5 (979-982)

HP: 2.10 (67-69)

P (Choose Naming, Solubilities, and Boiling Points)

TQ (Just the first couple sections on alcohols)

Aldehydes and Ketones

Carbonyl group is -C=O

Aldehyde has 1 H and at least 1 C bonded to the C

Ketones have 2 Cs bonded to the C

The carbonyl group is polar

BLB: 25.6 (982-983)

HP: 4.6 (64-65), 23.5 (969-970)

P (Look through for overview of aldehydes and ketones)

P (Look through quickly about the carbonyl group)

TQ (Carbonly group - just the beginning)

TQ (Naming of aldehydes and ketones)

TQ (a variety of functional groups. Try the Mission several times - new examples come up)

Carbohydrates and cellulose

The name carbohydrate comes from the empirical (simplest, non-structural) formulas which can usually be written as a hydrate of carbon, C_x(H₂O)_y

Carbohydrates are not hydrates of C. They are polyhydroxy aldehydes and ketones

Simple carbohydrates taste sweet and are called sugars

The simplest sugars are called monosaccharides

We are interested in glucose, a 6-C polyhydroxy aldehyde

Glucose can be written in a linear form

Glocose can exist as a ring structure

Disaccharides

Joining of two monosaccharides

-OH group on one molecule adds to the C=O group on the other molecule, forming a bond and eliminating a molecule of water

Polysaccharides

Many similar bonds between monosaccharides called polysaccharides

Starch and cellulose are polysaccharides made up from glucose units, the difference being in the way the glucose units bond in three dimensions

BLB: 25.10 (995-999)

HP: 23.8 (975-980)

P (Carbohydrates on up to cellulose)

C&A Science for Handpapermakers Vol I

C&A Biomolecules: Cellulose

TQ (Carbohydrates and Cellulose)

Binding in paper

Surfaces of like material 'stick' together without any cementing substance = cohesion or to cohere, co being Latin for together

Coherence of cellulose fibers is largely from H bonds

Also mechanical binding - entanglement of fibrils on surfaces of fibers important in papermaking

Unlike surfaces - to adhere, ad meaning to.

Wet paper dried on glass

Also largely H bonds - in this case H on cellulose to O atoms in SiO2 of the glass

Frictional binding

At the torn edge of a sheet of paper, hard to pull a fiber out in the direction of the plane of the sheet

Easier to lift off a fiber lying on and protruding from the surface of the sheet

Unbeaten or raw pulp, no fibrils, fibers are relatively smooth and lift off as lint

Strength in the plane of the paper is from H bonds and van der Waals forces from where fibers dried together

Coherence comes mostly from the fiber fibrils on the surface of the fibers - small diameter of fibrils leads to increase in the contact area

Also beaten fibers are somewhat rough (not smooth) and interwoven, e.g. on macroscopic scale is a splice in a nylon rope

"These considerations suggest that the cohesiveness of the fibers in a sheet of paper plays its part in strengthening paper, not directly, but indirectly by providing mutual lateral frictional forces between adjacent fibrils and fibers" Clark, pg 30.

As paper is pressed, particularly commercially, fibers squeeze into each other where the cross, forming mutually lapped joints. Therefore, when trying to pull out a fiber from paper, fibers usually break.

Reformed bonds

Main idea is that two surfaces have been joined by H or vdW bonds

Then the two surfaces are separated

Unless some other species come in and join at the binding sites of the separated surfaces, then the surfaces are 'setup' to rejoin

Cellulose fiber in water is bruised or split internally as being beaten to make pulp

Water molecules depart as the fiber dries, adjacent surfaces of the fiber (or fibers) usually recombine via H bonding, leaving a very strong fiber

"Rebonding of split cellulose surfaces is to be expected because the surface molecules of a split in the fiber are perfectly oriented with respect to each other and have the same configurations. Consequently, unless displaced, the split surfaces prefer to rebond together as the water dries off, rather than remain bonded to a monolyaer of water molecules that do not have the same spacing as the cellulose molecules." Clark, pg 31