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Food Packaging > Lecture 3: Paper > Flashcards

Lecture 3: Paper Flashcards

(65 cards)

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1
Q

describe the composition of cellulose

A
  • 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
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2
Q

cellulose is the main component of what?

A

cotton and wood

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3
Q

cellulose is difficult to process in ____ or as a ____

A

solution; melt

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4
Q

define polymer

A

large molecules made up of many repeating units

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5
Q

define monomer

A

molecule that combines with others (identical or different) by covalent bonds to form a polymer

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6
Q

how are synthetic polymers developed?

A

by chemists in labs and manufatured in factories

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7
Q

what are examples of synthetic polymers?

A

rubber
nylon
polyethylene

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8
Q

how are biological molecules used as natural polymers produced?

A

by organisms in their cells

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9
Q

what are examples of biological/natural polymers?

A

cellulose
starch
chitin
proteins

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10
Q

what are 3 main sources of cellulose?

A
  • wood
  • cotton, linen, straw (minor)
  • recycled paper (shorter fibers)
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11
Q

what are 2 main types of wood that sources cellulose?

describe each.

A
  1. hardwood (maple and birch)
    - short fibers
    - smooth paper, good printing, low strength
  2. softwood (pine and spruce)
    - longer fibers
    - strong paper, good fold strength, poor printing
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12
Q

what are some main fibers found in the structure of wood?

A
  • lignin
  • hemicellulose
  • cellulose
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13
Q

what are the 3 main layers of wood?

what does each layer consist of?

A
  1. middle lamella (top): contains pectin
  2. primary wall ( middle): contains cellulose microfibril, hemicellulose and soluble protein
  3. plasma membrane (bottom)
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14
Q

pulping is used to extract _____

A

cellulose

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15
Q

describe mechanical pulping

A
  • 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
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16
Q

describe chemical pulping

A
  • 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
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17
Q

describe chemical pulp furnishing

A

wood is cooked with chemicals to separate the cellulose

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18
Q

what are 2 common processes of chemical pulp furnishing

A
  1. kraft process (aka sulfate pulp process)

2. sulfite process

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19
Q

which results in a stronger paper?

a) kraft process
b) sulfite process

A

kraft

german word for strong

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20
Q

describe the properties of pump from the kraft process (compared to sulphite process)

A

chemicals used: alkaline
color of paper: brown
strength: higher sheet strength
bleaching: harder to bleach

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21
Q

describe the properties of pump from the sulphite process (compared to kraft process)

A

chemicals used: acidic
color of paper: white
strength: lower sheet strength
bleaching: easier to bleach and refine

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22
Q

describe main steps in the kraft process

A
  1. cooking
  2. washing
  3. bleaching
  4. evaporation
  5. recovery boiler
  6. recausticizing
  7. lime kiln
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23
Q

what are the main components of the kraft liquor cycle

A

cooking/washing

caustizing

lime kiln

evaporation and burning

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24
Q

what color is the liquor after caustizing and before cooking and washing?

A

white

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25
what color is the liquor after cooking/washing but before evaporation/burning?
black
26
what color is the liquor after evaporation/burning and before caustizing?
green
27
what treatments of pulp can be done to improve performance of the paper?
1. bleaching 2. mechanical beating 3. acid treating
28
what chemicals are used in bleaching of pulp?
Cl2 NaOH ClO2 H2O2 (in this order)
29
what is the function of bleaching pulp?
- improves physical and optical properties (whiteness and brightness) by removing residual lignin - weakens fibers - reduces sheet strength
30
the dark color of the pulp is mainly due to what? how is this removed?
residual lignin removed during bleaching
31
what are two names of machinery for pulp treatments?
1. hollander beater | 2. conical refiner (Jordan refiner)
32
a low amount of mechanical beating results in what properties of paper?
paper that: - absorbs well - resists tears - has low burst and tensile strength
33
a high amount of mechanical beating results in what properties of paper?
- high burst and tensile strength | - low tear resistance (glassine)
34
mechanical beating improves resistance of what?
water and grease resistance
35
what is sizing?
starch and alum
36
what does sizing improve?
- water resistance - printability - adhesive properties
37
describe the function of sulfuric acid bath (parchment)
can matt the fibers and improve grease resistance
38
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 ```
39
what is the effect of adding titania to paper?
increases opacity and brightens
40
what is the effect of adding CMC to paper?
increases water resistance
41
what is the effect of adding Talc to paper?
greasy/soapy feel increases high finish
42
what is the effect of adding china clay or limestone to paper?
fills and coats
43
what is the effect of adding polyethylene to paper?
increases water resistance
44
what is the effect of adding guar gum to paper?
increases dry strength
45
what is the effect of adding guar gum to paper?
increases dry strength
46
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
47
tear is easier in which direction of the paper?
along the grain rather than across it
48
stiffness is greater in which direction of the paper?
along the grain
49
fold endurance is greater in which direction of the paper?
across the grain
50
what are 2 directions of paper?
1. along the grain (machine direction) | 2. across the grain (cross direction)
51
paper and paperboard are made from what?
matted cellulose fibers
52
what is the main difference between paper and paperboard
thickness
53
what is the primary use for paper?
primary containers, bags, labels
54
what is the primary use for paperboard
secondary containers
55
what is the thickness of paper? of paperboard?
paper: under 0.012 inches paperboard: over 0.012 inches
56
what are common uses for paperboard?
1. folding cartons 2. liquid type containers 3. fiber cans 4. carded displays
57
define blank
cut shape that will become the carton
58
define score
the crease along which the adjacent parts of a carton blank can be folded
59
define crease
to score
60
define cut score
to cut partly through a sheet of paperboard
61
what are 2 requirements of the blank shape?
1. result in a useful box | 2. be compatible with machinery
62
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
63
what is the order of dimensions used when describing carton?
1. length 2. width 3. depth
64
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
65
what are advantages of paper and paperboard?
- inexpensive - versatile - easy to manufacture - printable - treatable - renewable and biodegradable

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