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Food Packaging > Testing & QA > Flashcards

Testing & QA Flashcards

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1
Q

What does an “instron” evaluate?

A

mechanical properties of materials

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2
Q

The main parts of an instron: (5)

A 
frame
crosshead
load cell
controller
clamp
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3
Q

How does an instron evaluate the mechanical properties of a material?

A 
apply some form of stress to material
measure variables (force, deformation, time) with electronic measurement

graphical + calculated results

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4
Q

What is tensile testing?

A

gradual (controlled) increase in UNIAXIAL TENSION on sample (‘pull’ the sample apart) until failure (breaks)

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5
Q

What material types are usually subject to tension tests?

A

films

fibres

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6
Q

What is compressive testing?

A

measure ability of material to withstand AXIAL PUSHING FORCES (‘squish’ material)

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7
Q

Samples in compressive testing are in what shape?

A

rectangular, circular, tubular, or irregular

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8
Q

Tensile testing samples are often in what shape?

A

Dogbone sample (wide at edges for clamps to hold, thin in the centre)

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9
Q

In tensile testing, polymers can be classified as: (3)

A

brittle
plastic
highly elastic (elastomeric)

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10
Q

The greater the strain applied on the material, the greater the ____ the material experiences

A

stress

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11
Q

Tensile strength can be expressed with a stress - _____ curve

A

strain

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12
Q

What is stress? What is strain?

A

stress: applied force on a body/the internal distribution of forces (the material)

Strain: the response of the material to force (the deformation)

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13
Q

The stress vs strain response in brittle materials?

A

very little increase with strain; stress will increase with increased applied force until it breaks

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14
Q

As strain is increased, stress will (increase/decrease)

A

decrease

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15
Q

Why does stress stay low in highly elastic materials, despite the increase in applied force?

A

strain increases (it deforms) in response

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16
Q

plastic is a combination of ___ and ____ structures

A

crystalline

amorphous

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17
Q

The molecular structural changes as plastic stretches: (5)

A
  1. crystalline sections (chain folded lamellae) connected by amorphous material
  2. ELONGATION: amorphous ‘tie chains’ elongated (stretched)
  3. TILTING: lamella tilted (stretched straight)
  4. SEPARATION: crystalline block segments separate (lamella broken up)
  5. ORIENTATION: block segments + tie chains stretched straight
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18
Q

the initial structure of plastic:

A

crystalline sheets (lamellae) connected by amorphous material (tie chains)

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19
Q

Plastic deformation is (reversible/irreversible).

Elastic deformation is (reversible/irreversible).

A 
plastic = irreversible
elastic = reversible
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20
Q

The ___ ____ separates plastic behaviour from elastic behaviour

A

YIELD POINT

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21
Q

What happens after a material is stretched beyond its yield point?

A

plastic range -> no longer reversible (permanent deformation)

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22
Q

Compare the structure of an elastomer, before and after stretching:

A

before: amorphous chains (kinked, heavily cross-linked)

After: chains straightened, still cross-linked

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23
Q

The greater the amount of crystalline structure, the (greater/less) the elasticity

A

less

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24
Q

2 tests used for texture testing:

A

stress relaxation

creep recovery

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25
Q

Describe the stress relaxation experiment:

A

strain applied instantly (constant amount)

monitor stress over time (decreases with time down to zero)

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26
Q

What is the creep recovery experiment?

A

stress applied instantly (constant amount) for SPECIFIC time period
monitor strain over time
remove stress -> monitor strain over time (decreases)

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27
Q

Describe the pattern of strain as stress is applied in the creep recovery experiment:

A

CREEP ZONE: increasing

RECOVERY ZONE: decreases exponentially (plateaus)

28
Q

A material in the creep recovery experiment showed a strain level that decreased very little in the recovery zone. This material is (elastic/inelastic)

A

inelastic

29
Q

What machines are used for compressive testing? (2)

A

compression plate

puncture

30
Q

What are texture tests useful for? (3)

A

quality control
customer acceptance
R & D

31
Q

The objective measurement done with machines correlates with ____ ____ (qualitative)

A

sensory panel

ORAL vs TPA:
initial - hardness
masticatory - chewiness

NON-ORAL vs COMPRESS:
feel/touch - deformation

32
Q

hardness tests correspond to what sensory evaluation?

A

initial (oral)

33
Q

Compression tests (deformation) correspond to what sensory evaluation?

A

Non-oral: feel/touch

34
Q

Permeability is described by: _____

A

the Flux (J) of gas across a film

35
Q

What factors influence gas transmission?

A 
temperature
RH%
thickness
plasticizer levels
microperforation
creases
 chemical nature of polymer vs gas (size, shape, polarity?)
36
Q

The 2 most common permeation measures for food packaging? give the units

A 
water vapor transmission (g/m2/24hr at given T, RH%, thickness)
gas transmission (cm3/m2/24hr at given T, thickness, P difference 1 atm)
37
Q

Gas transmission is measured over ____ hours, with a difference in pressure of _____

A

24 hrs

1 atm

38
Q

2 gravimetric systems for the water vapor permeability test:

A
  1. sealed chamber: dessication utensil (contains dessicant) above distilled water chamber on balance - test material covers water chamber. (measure weight loss as water escapes)
  2. test sample stretched across chamber, lower room contains dessicant in a cup (on weight sensor). Upper room has input of humid N2 -> carry moisture in, diffuse down into dessicant (measure weight gain)
39
Q

Only RH and temperature values within the ____ ____ can be tested. Why?

A

Working range

outside this range results can no longer be accurately determined by instrument

40
Q

Ranges of WVTR for high, semi high, and medium barrier properties? (at 38C, 90%RH)

A

high: <10
semi-high: 10-30
medium: 30-100

41
Q

Ranges of WVTR for low, very low, and extremely low barrier properties? (38C, 90% RH)

A

Low: 100-200
Very low: 200-300
Extremely low: >300

42
Q

Examples of high MOISTURE barrier materials:

A

glass, aluminum, HDPE, PVDC, PP, LDPE, oriented PET

43
Q

examples of medium MOISTURE barrier materials:

A

EVOH, Surlyn, Rigid PVC, non-oriented PET

44
Q

How can the moisture barrier properties of PET be improved?

A

orientation

45
Q

What are some low MOISTURE barrier materials?

A

PS
oriented/non-oriented nylon
polycarbonate

46
Q

The 2 types of gas permeability tests:

A

equal pressure method

differential presure method

47
Q

Describe the equal pressure method for gas permeability testing:

A

test cell divided by sample film; 2 independent airflows on either side (feed side = testing gas, permeate side = sweep gas)

Test gas will diffuse through material -> carried to detector by sweep gas

48
Q

Describe the differential pressure method for gas permeability testing:

A

chamber divided by sample film; control valve maintains a pressure difference (100kpa vs vacuum)

gas will diffuse into area of lower pressure (detect with pressure sensors)

49
Q

What are the oxygen transmission rates for high, semi high, and medium gas barrier materials? (1atm, 23C, 0%RH)

A

high: <50
semi-high: 50-200
medium: 200-5000

50
Q

What are the oxygen transmission rates for low, very low, and extremely low gas barrier materials? (1atm, 23C, 0%RH)

A

low: 5000-10,000
very low: 10,000 -15,000
extremely low: >15,000

51
Q

What are some materials with high oxygen barrier properties?

A

glass
aluminum
EVOH (0% RH)
PVDC

52
Q

What are some materials with medium oxygen barrier properties?

A

orient/non-orient nylon
non-oriented PET
rigid PVC
EVOH (100% RH)

53
Q

What are some materials with low oxygen barrier properties?

A 
PS
HDPE
PP
polycarbonate
surlyn
LDPE
54
Q

how is the OTR of EVOH affected by humidity?

A

0% RH: high gas barrier
100% RH: medium gas barrier
(increased humidity lead to poorer gas barrier properties)

55
Q

T/F: a material that is gas-permeable is not necessarily water permeable

A

true

56
Q

What do thermal analysis instruments measure? (4)

A

heat flow, weight loss, dimension change, mechanical properties
(as a function of temperature)

57
Q

What properties are characterized by thermal analysis? (7)

A 
melting
oxidation
decomposition
volatilization
coefficient of thermal expansion
modulus
58
Q

What is TGA?

A

thermogravimetric analysis

mass of sample measured over time, as temp changes

59
Q

What information can a TGA provide? (4)

A

info about phase transitions, absorption/desorption, thermal decomposition, solid-gas rxn

60
Q

What is DMA?

A

dynamic mechanical analysis - mechanically deform sample -> measure sample response (response as function of temp or time)

61
Q

3 measures given by DMA?

A

E’ (storage modulus)
E’’ (loss modulus)
tan sigma (tangent of phase difference)

62
Q

What is E’?

A

storage modulus - elastic component (related to stiffness)

63
Q

What is loss modulus?

A

E’’ - viscous component - related to sample’s ability to dissipate mechanical energy w/ molecular motion

64
Q

What is tangent of phase difference?

A

relationship between elastic vs inelastic components

65
Q

Types of deformation used in DMA: (4)

A

dual/single cantilever
3-point bend
tension
compression

Food Packaging (11 decks)

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