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Testing & QA Flashcards

(65 cards)

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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
Describe the stress relaxation experiment:
strain applied instantly (constant amount) | monitor stress over time (decreases with time down to zero)
26
What is the creep recovery experiment?
stress applied instantly (constant amount) for SPECIFIC time period monitor strain over time remove stress -> monitor strain over time (decreases)
27
Describe the pattern of strain as stress is applied in the creep recovery experiment:
CREEP ZONE: increasing | RECOVERY ZONE: decreases exponentially (plateaus)
28
A material in the creep recovery experiment showed a strain level that decreased very little in the recovery zone. This material is (elastic/inelastic)
inelastic
29
What machines are used for compressive testing? (2)
compression plate | puncture
30
What are texture tests useful for? (3)
quality control customer acceptance R & D
31
The objective measurement done with machines correlates with ____ ____ (qualitative)
sensory panel ORAL vs TPA: initial - hardness masticatory - chewiness NON-ORAL vs COMPRESS: feel/touch - deformation
32
hardness tests correspond to what sensory evaluation?
initial (oral)
33
Compression tests (deformation) correspond to what sensory evaluation?
Non-oral: feel/touch
34
Permeability is described by: _____
the Flux (J) of gas across a film
35
What factors influence gas transmission?
``` temperature RH% thickness plasticizer levels microperforation creases chemical nature of polymer vs gas (size, shape, polarity?) ```
36
The 2 most common permeation measures for food packaging? give the units
``` 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
Gas transmission is measured over ____ hours, with a difference in pressure of _____
24 hrs | 1 atm
38
2 gravimetric systems for the water vapor permeability test:
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
Only RH and temperature values within the ____ ____ can be tested. Why?
Working range | outside this range results can no longer be accurately determined by instrument
40
Ranges of WVTR for high, semi high, and medium barrier properties? (at 38C, 90%RH)
high: <10 semi-high: 10-30 medium: 30-100
41
Ranges of WVTR for low, very low, and extremely low barrier properties? (38C, 90% RH)
Low: 100-200 Very low: 200-300 Extremely low: >300
42
Examples of high MOISTURE barrier materials:
glass, aluminum, HDPE, PVDC, PP, LDPE, oriented PET
43
examples of medium MOISTURE barrier materials:
EVOH, Surlyn, Rigid PVC, non-oriented PET
44
How can the moisture barrier properties of PET be improved?
orientation
45
What are some low MOISTURE barrier materials?
PS oriented/non-oriented nylon polycarbonate
46
The 2 types of gas permeability tests:
equal pressure method | differential presure method
47
Describe the equal pressure method for gas permeability testing:
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
Describe the differential pressure method for gas permeability testing:
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
What are the oxygen transmission rates for high, semi high, and medium gas barrier materials? (1atm, 23C, 0%RH)
high: <50 semi-high: 50-200 medium: 200-5000
50
What are the oxygen transmission rates for low, very low, and extremely low gas barrier materials? (1atm, 23C, 0%RH)
low: 5000-10,000 very low: 10,000 -15,000 extremely low: >15,000
51
What are some materials with high oxygen barrier properties?
glass aluminum EVOH (0% RH) PVDC
52
What are some materials with medium oxygen barrier properties?
orient/non-orient nylon non-oriented PET rigid PVC EVOH (100% RH)
53
What are some materials with low oxygen barrier properties?
``` PS HDPE PP polycarbonate surlyn LDPE ```
54
how is the OTR of EVOH affected by humidity?
0% RH: high gas barrier 100% RH: medium gas barrier (increased humidity lead to poorer gas barrier properties)
55
T/F: a material that is gas-permeable is not necessarily water permeable
true
56
What do thermal analysis instruments measure? (4)
heat flow, weight loss, dimension change, mechanical properties (as a function of temperature)
57
What properties are characterized by thermal analysis? (7)
``` melting oxidation decomposition volatilization coefficient of thermal expansion modulus ```
58
What is TGA?
thermogravimetric analysis | mass of sample measured over time, as temp changes
59
What information can a TGA provide? (4)
info about phase transitions, absorption/desorption, thermal decomposition, solid-gas rxn
60
What is DMA?
dynamic mechanical analysis - mechanically deform sample -> measure sample response (response as function of temp or time)
61
3 measures given by DMA?
E' (storage modulus) E'' (loss modulus) tan sigma (tangent of phase difference)
62
What is E'?
storage modulus - elastic component (related to stiffness)
63
What is loss modulus?
E'' - viscous component - related to sample's ability to dissipate mechanical energy w/ molecular motion
64
What is tangent of phase difference?
relationship between elastic vs inelastic components
65
Types of deformation used in DMA: (4)
dual/single cantilever 3-point bend tension compression

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