what does instron do?
evaluates mechanical properties (force, deformation, time) of materials and components
what tests does instron do?
- tensile testing
2. compressive testing
describe tensile testing by instron
what does it sample?
small sample is subjected to a controlled and gradually increasing uniaxial tension until failure
samples film and fiber
describe compressive strength
what does it sample?
the capacity of a material to withstand axially directed pushing forces
samples: retangular, circular, tubular and irregular materials
what are 3 typical classes of polymers based on their tensile strength? how is each characterized?
brittle: reaches high stress with low strain
plastic: increases stress with low strain, and then plateaus with increasing strain
highly elastic (elastomeric): gradually increases stress with increasing strain
what is the mechanism of plastic deformation in semicrystalline polymers?
- two adjacent chains are folded
- elongation of amorphous tie chains
- tilting of lamellar chain folds
- separation of crystalline block segments
- orientation of block segments and tie chains
describe what happens when an elastomer is put under increasing straining
- initially, amorphous chains are kinked and heavily cross linked (at low strain)
- final: chains are straight and still cross linked (at high strain)
elastomer undergoes reversible deformation between the two phases at intermediate strain
what was used to text texture?
- stress relaxation experiment
2. creep recovery experiment
describe stress relaxation experiment
- constant stress is applied to sample
- Stress is monitored as a function of time
- showed that stress starts at a high value and decreases with time to zero
describe creep recover experiment
- constant stress is applied to a sample instantaneously for a specific time
- measured strain
showed that….
- the strain gradually increased during the creep zone (during constant stress)
- once stress is stopped, there is a recovery zone where the strain gradually decreases
- rate of decrease in recovery depends on elasticity of the material
- higher elastic decreases strain faster than lower elastic
when transmission rate of water vapour increases in a film, what happens to the barrier properties?
decreases (inverse rel)
when transmission rate of O2 increases in a film, what happens to the barrier properties?
decreases (inverse rel)
instruments of thermal analysis measures what?
heat flow
wt loss
dimension change
mechanical properties (melting, crystallization, glass transitions, cross linking, etc…)
thermal analysis experiments allow the user to examine what?
performance composition processing stability molecular structure
what is TGA?
what does it measure?
thermogravimetric analysis
mass of a sample measured over time as the temp changes
gives information about phase transitions, absorption and desorption thermal decomposition, solid gas rxns
what is DMA?
dynamic mechanical analysis
mechanically deforms a sample and measures the sample response
response to the deformation can be monitored as a function of temp or time
in DMA, what is E’? what is E’’? what is tan sigma?
E’
- storage modulus
- elastic component related to the sample’s stiffness
E’’
- loss modulus
- viscous component
- related to the sample’s ability to dissipate mechanical energy through molecular motion
tan sigma
- tangent of phase difference
- relationship between elastic and inelastic components
in thermal analysis, as frequency of test increases, when do molecular relaxations occur?
only at higher temp
what are the effects of r.h. on glass transition of Nylon 6?
nylon 6 is strongly plasticized by water
thus mechanical properties will be dependent on the surrounding r.h.
how can you characterize packaging films using creep recovery?
- in thermoforming, the film is pulled down into a heated mold to form a shape
- a thermoformed film has to keep its shape when formed to fit over the pdt
- through creep-recovery measurements at the forming temp, you can predict if the fill will have sufficient elasticity to hold its shape to produce a stable pdt
