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Food Packaging > Lecture 3: Paper > Flashcards

Lecture 3: Paper Flashcards

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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
Q

what color is the liquor after cooking/washing but before evaporation/burning?

A

black

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26
Q

what color is the liquor after evaporation/burning and before caustizing?

A

green

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27
Q

what treatments of pulp can be done to improve performance of the paper?

A
  1. bleaching
  2. mechanical beating
  3. acid treating
28
Q

what chemicals are used in bleaching of pulp?

A

Cl2
NaOH
ClO2
H2O2

(in this order)

29
Q

what is the function of bleaching pulp?

A
  • improves physical and optical properties (whiteness and brightness) by removing residual lignin
  • weakens fibers
  • reduces sheet strength
30
Q

the dark color of the pulp is mainly due to what?

how is this removed?

A

residual lignin

removed during bleaching

31
Q

what are two names of machinery for pulp treatments?

A
  1. hollander beater

2. conical refiner (Jordan refiner)

32
Q

a low amount of mechanical beating results in what properties of paper?

A

paper that:

  • absorbs well
  • resists tears
  • has low burst and tensile strength
33
Q

a high amount of mechanical beating results in what properties of paper?

A
  • high burst and tensile strength

- low tear resistance (glassine)

34
Q

mechanical beating improves resistance of what?

A

water and grease resistance

35
Q

what is sizing?

A

starch and alum

36
Q

what does sizing improve?

A
  • water resistance
  • printability
  • adhesive properties
37
Q

describe the function of sulfuric acid bath (parchment)

A

can matt the fibers and improve grease resistance

38
Q

what are examples of chemicals used to improve other factors (eg. color, opacity, stiffness, waterproofing)

A 
titania
CMC
talc
china clay (Kaolin)
limestone CaCO3
polyethylene 
guar gum
39
Q

what is the effect of adding titania to paper?

A

increases opacity and brightens

40
Q

what is the effect of adding CMC to paper?

A

increases water resistance

41
Q

what is the effect of adding Talc to paper?

A

greasy/soapy feel

increases high finish

42
Q

what is the effect of adding china clay or limestone to paper?

A

fills and coats

43
Q

what is the effect of adding polyethylene to paper?

A

increases water resistance

44
Q

what is the effect of adding guar gum to paper?

A

increases dry strength

45
Q

what is the effect of adding guar gum to paper?

A

increases dry strength

46
Q

describe the dry end treatments in paper making with the fourdrinier machine

A
  • 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
Q

tear is easier in which direction of the paper?

A

along the grain rather than across it

48
Q

stiffness is greater in which direction of the paper?

A

along the grain

49
Q

fold endurance is greater in which direction of the paper?

A

across the grain

50
Q

what are 2 directions of paper?

A
  1. along the grain (machine direction)

2. across the grain (cross direction)

51
Q

paper and paperboard are made from what?

A

matted cellulose fibers

52
Q

what is the main difference between paper and paperboard

A

thickness

53
Q

what is the primary use for paper?

A

primary containers, bags, labels

54
Q

what is the primary use for paperboard

A

secondary containers

55
Q

what is the thickness of paper? of paperboard?

A

paper: under 0.012 inches
paperboard: over 0.012 inches

56
Q

what are common uses for paperboard?

A
  1. folding cartons
  2. liquid type containers
  3. fiber cans
  4. carded displays
57
Q

define blank

A

cut shape that will become the carton

58
Q

define score

A

the crease along which the adjacent parts of a carton blank can be folded

59
Q

define crease

A

to score

60
Q

define cut score

A

to cut partly through a sheet of paperboard

61
Q

what are 2 requirements of the blank shape?

A
  1. result in a useful box

2. be compatible with machinery

62
Q

when are cartons easiest to break open?

why?

A

when they are freshly cut and scored

with time, fibers set in the folds and make break-open harder

63
Q

what is the order of dimensions used when describing carton?

A
  1. length
  2. width
  3. depth
64
Q

what should be considered when testing paper and paperboard?

A
  • 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
Q

what are advantages of paper and paperboard?

A
  • inexpensive
  • versatile
  • easy to manufacture
  • printable
  • treatable
  • renewable and biodegradable

Food Packaging (11 decks)

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