Lecture 3: Paper Flashcards
describe the composition of cellulose
- linear chain CHO
- generated from repeating beta-1,4-glucan unit covalently linked through acetal functions between OH group of C4 and C1 carbon atoms
cellulose is the main component of what?
cotton and wood
cellulose is difficult to process in ____ or as a ____
solution; melt
define polymer
large molecules made up of many repeating units
define monomer
molecule that combines with others (identical or different) by covalent bonds to form a polymer
how are synthetic polymers developed?
by chemists in labs and manufatured in factories
what are examples of synthetic polymers?
rubber
nylon
polyethylene
how are biological molecules used as natural polymers produced?
by organisms in their cells
what are examples of biological/natural polymers?
cellulose
starch
chitin
proteins
what are 3 main sources of cellulose?
- wood
- cotton, linen, straw (minor)
- recycled paper (shorter fibers)
what are 2 main types of wood that sources cellulose?
describe each.
- hardwood (maple and birch)
- short fibers
- smooth paper, good printing, low strength - softwood (pine and spruce)
- longer fibers
- strong paper, good fold strength, poor printing
what are some main fibers found in the structure of wood?
- lignin
- hemicellulose
- cellulose
what are the 3 main layers of wood?
what does each layer consist of?
- middle lamella (top): contains pectin
- primary wall ( middle): contains cellulose microfibril, hemicellulose and soluble protein
- plasma membrane (bottom)
pulping is used to extract _____
cellulose
describe mechanical pulping
- method of extracting cellulose
- cheaper than chemical pulping
- breaks down fibers
- does not remove lignin
- produces weak paper with a poor color and prone to discoloration
- used for newsprint and egg cartons
describe chemical pulping
- a method of extracting cellulose
- more expensive than mechanical pulping
- low fiber breakdown
- lignin is dissolved
- strong pulp
- strength and properties vary with type of chemical process
- used for brown paper towels
describe chemical pulp furnishing
wood is cooked with chemicals to separate the cellulose
what are 2 common processes of chemical pulp furnishing
- kraft process (aka sulfate pulp process)
2. sulfite process
which results in a stronger paper?
a) kraft process
b) sulfite process
kraft
german word for strong
describe the properties of pump from the kraft process (compared to sulphite process)
chemicals used: alkaline
color of paper: brown
strength: higher sheet strength
bleaching: harder to bleach
describe the properties of pump from the sulphite process (compared to kraft process)
chemicals used: acidic
color of paper: white
strength: lower sheet strength
bleaching: easier to bleach and refine
describe main steps in the kraft process
- cooking
- washing
- bleaching
- evaporation
- recovery boiler
- recausticizing
- lime kiln
what are the main components of the kraft liquor cycle
cooking/washing
caustizing
lime kiln
evaporation and burning
what color is the liquor after caustizing and before cooking and washing?
white
what color is the liquor after cooking/washing but before evaporation/burning?
black
what color is the liquor after evaporation/burning and before caustizing?
green
what treatments of pulp can be done to improve performance of the paper?
- bleaching
- mechanical beating
- acid treating
what chemicals are used in bleaching of pulp?
Cl2
NaOH
ClO2
H2O2
(in this order)
what is the function of bleaching pulp?
- improves physical and optical properties (whiteness and brightness) by removing residual lignin
- weakens fibers
- reduces sheet strength
the dark color of the pulp is mainly due to what?
how is this removed?
residual lignin
removed during bleaching
what are two names of machinery for pulp treatments?
- hollander beater
2. conical refiner (Jordan refiner)
a low amount of mechanical beating results in what properties of paper?
paper that:
- absorbs well
- resists tears
- has low burst and tensile strength
a high amount of mechanical beating results in what properties of paper?
- high burst and tensile strength
- low tear resistance (glassine)
mechanical beating improves resistance of what?
water and grease resistance
what is sizing?
starch and alum
what does sizing improve?
- water resistance
- printability
- adhesive properties
describe the function of sulfuric acid bath (parchment)
can matt the fibers and improve grease resistance
what are examples of chemicals used to improve other factors (eg. color, opacity, stiffness, waterproofing)
titania CMC talc china clay (Kaolin) limestone CaCO3 polyethylene guar gum
what is the effect of adding titania to paper?
increases opacity and brightens
what is the effect of adding CMC to paper?
increases water resistance
what is the effect of adding Talc to paper?
greasy/soapy feel
increases high finish
what is the effect of adding china clay or limestone to paper?
fills and coats
what is the effect of adding polyethylene to paper?
increases water resistance
what is the effect of adding guar gum to paper?
increases dry strength
what is the effect of adding guar gum to paper?
increases dry strength
describe the dry end treatments in paper making with the fourdrinier machine
- paper is rolled with calendar rolls to smooth the surface
- paper can be coated to improve surface
- clay coating fills the gaps and improves whiteness and printability
- other coatings can be used to improve surface gloss, water resistance or other properties
tear is easier in which direction of the paper?
along the grain rather than across it
stiffness is greater in which direction of the paper?
along the grain
fold endurance is greater in which direction of the paper?
across the grain
what are 2 directions of paper?
- along the grain (machine direction)
2. across the grain (cross direction)
paper and paperboard are made from what?
matted cellulose fibers
what is the main difference between paper and paperboard
thickness
what is the primary use for paper?
primary containers, bags, labels
what is the primary use for paperboard
secondary containers
what is the thickness of paper? of paperboard?
paper: under 0.012 inches
paperboard: over 0.012 inches
what are common uses for paperboard?
- folding cartons
- liquid type containers
- fiber cans
- carded displays
define blank
cut shape that will become the carton
define score
the crease along which the adjacent parts of a carton blank can be folded
define crease
to score
define cut score
to cut partly through a sheet of paperboard
what are 2 requirements of the blank shape?
- result in a useful box
2. be compatible with machinery
when are cartons easiest to break open?
why?
when they are freshly cut and scored
with time, fibers set in the folds and make break-open harder
what is the order of dimensions used when describing carton?
- length
- width
- depth
what should be considered when testing paper and paperboard?
- basis wt: actual wt per unit area
- thickness
- folding endurance: bending stiffness and durability
- puncture resistance: triangular pyramid puncture
- bursting strength
- tensile strength
- water vapor permeability
what are advantages of paper and paperboard?
- inexpensive
- versatile
- easy to manufacture
- printable
- treatable
- renewable and biodegradable
