Testing & QA Flashcards
What does an “instron” evaluate?
mechanical properties of materials
The main parts of an instron: (5)
frame crosshead load cell controller clamp
How does an instron evaluate the mechanical properties of a material?
apply some form of stress to material measure variables (force, deformation, time) with electronic measurement
graphical + calculated results
What is tensile testing?
gradual (controlled) increase in UNIAXIAL TENSION on sample (‘pull’ the sample apart) until failure (breaks)
What material types are usually subject to tension tests?
films
fibres
What is compressive testing?
measure ability of material to withstand AXIAL PUSHING FORCES (‘squish’ material)
Samples in compressive testing are in what shape?
rectangular, circular, tubular, or irregular
Tensile testing samples are often in what shape?
Dogbone sample (wide at edges for clamps to hold, thin in the centre)
In tensile testing, polymers can be classified as: (3)
brittle
plastic
highly elastic (elastomeric)
The greater the strain applied on the material, the greater the ____ the material experiences
stress
Tensile strength can be expressed with a stress - _____ curve
strain
What is stress? What is strain?
stress: applied force on a body/the internal distribution of forces (the material)
Strain: the response of the material to force (the deformation)
The stress vs strain response in brittle materials?
very little increase with strain; stress will increase with increased applied force until it breaks
As strain is increased, stress will (increase/decrease)
decrease
Why does stress stay low in highly elastic materials, despite the increase in applied force?
strain increases (it deforms) in response
plastic is a combination of ___ and ____ structures
crystalline
amorphous
The molecular structural changes as plastic stretches: (5)
- crystalline sections (chain folded lamellae) connected by amorphous material
- ELONGATION: amorphous ‘tie chains’ elongated (stretched)
- TILTING: lamella tilted (stretched straight)
- SEPARATION: crystalline block segments separate (lamella broken up)
- ORIENTATION: block segments + tie chains stretched straight
the initial structure of plastic:
crystalline sheets (lamellae) connected by amorphous material (tie chains)
Plastic deformation is (reversible/irreversible).
Elastic deformation is (reversible/irreversible).
plastic = irreversible elastic = reversible
The ___ ____ separates plastic behaviour from elastic behaviour
YIELD POINT
What happens after a material is stretched beyond its yield point?
plastic range -> no longer reversible (permanent deformation)
Compare the structure of an elastomer, before and after stretching:
before: amorphous chains (kinked, heavily cross-linked)
After: chains straightened, still cross-linked
The greater the amount of crystalline structure, the (greater/less) the elasticity
less
2 tests used for texture testing:
stress relaxation
creep recovery
Describe the stress relaxation experiment:
strain applied instantly (constant amount)
monitor stress over time (decreases with time down to zero)
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)
Describe the pattern of strain as stress is applied in the creep recovery experiment:
CREEP ZONE: increasing
RECOVERY ZONE: decreases exponentially (plateaus)
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
What machines are used for compressive testing? (2)
compression plate
puncture
What are texture tests useful for? (3)
quality control
customer acceptance
R & D
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
hardness tests correspond to what sensory evaluation?
initial (oral)
Compression tests (deformation) correspond to what sensory evaluation?
Non-oral: feel/touch
Permeability is described by: _____
the Flux (J) of gas across a film
What factors influence gas transmission?
temperature RH% thickness plasticizer levels microperforation creases chemical nature of polymer vs gas (size, shape, polarity?)
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)
Gas transmission is measured over ____ hours, with a difference in pressure of _____
24 hrs
1 atm
2 gravimetric systems for the water vapor permeability test:
- sealed chamber: dessication utensil (contains dessicant) above distilled water chamber on balance - test material covers water chamber. (measure weight loss as water escapes)
- 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)
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
Ranges of WVTR for high, semi high, and medium barrier properties? (at 38C, 90%RH)
high: <10
semi-high: 10-30
medium: 30-100
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
Examples of high MOISTURE barrier materials:
glass, aluminum, HDPE, PVDC, PP, LDPE, oriented PET
examples of medium MOISTURE barrier materials:
EVOH, Surlyn, Rigid PVC, non-oriented PET
How can the moisture barrier properties of PET be improved?
orientation
What are some low MOISTURE barrier materials?
PS
oriented/non-oriented nylon
polycarbonate
The 2 types of gas permeability tests:
equal pressure method
differential presure method
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
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)
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
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
What are some materials with high oxygen barrier properties?
glass
aluminum
EVOH (0% RH)
PVDC
What are some materials with medium oxygen barrier properties?
orient/non-orient nylon
non-oriented PET
rigid PVC
EVOH (100% RH)
What are some materials with low oxygen barrier properties?
PS HDPE PP polycarbonate surlyn LDPE
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)
T/F: a material that is gas-permeable is not necessarily water permeable
true
What do thermal analysis instruments measure? (4)
heat flow, weight loss, dimension change, mechanical properties
(as a function of temperature)
What properties are characterized by thermal analysis? (7)
melting oxidation decomposition volatilization coefficient of thermal expansion modulus
What is TGA?
thermogravimetric analysis
mass of sample measured over time, as temp changes
What information can a TGA provide? (4)
info about phase transitions, absorption/desorption, thermal decomposition, solid-gas rxn
What is DMA?
dynamic mechanical analysis - mechanically deform sample -> measure sample response (response as function of temp or time)
3 measures given by DMA?
E’ (storage modulus)
E’’ (loss modulus)
tan sigma (tangent of phase difference)
What is E’?
storage modulus - elastic component (related to stiffness)
What is loss modulus?
E’’ - viscous component - related to sample’s ability to dissipate mechanical energy w/ molecular motion
What is tangent of phase difference?
relationship between elastic vs inelastic components
Types of deformation used in DMA: (4)
dual/single cantilever
3-point bend
tension
compression
