Shear-induced crystallization of polyethylene (see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced.

Shear-induced crystallization of polyethylene

(see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced crystallization of polyethylene studied by small- and wide-angle X-ray scattering (SAXS/WAXS) techniques)

In situ study of development of shear-induced macrostructure of PE

injection molding ––> shear flow in polymer

changes crystallization kinetics & morphology

chain alignment ––> 'shish kebab' structure

(see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced crystallization of polyethylene studied by small- and wide-angle X-ray scattering (SAXS/WAXS) techniques)

In situ study of development of shear-induced macrostructure of PE

synchrotron radiation using shear cell & heating stage

5 sec/frame – after shear (100 pulses/sec for 5 & 10 sec)


crystallization temperature

Results

stacking of lamellae along shear direction


lower MW - less orientation

shear direction

More results

invariant vs crystallization time


Pores in polymers & carbons

(see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials)

Banded spherulites ––> carbon foams

crystallized blend of maleic anhydride (MA) & polyacrylonitrile (PAN)

bands are ~ 3.5 mm in width in this system (can use SAXS)

sublimate MA & pyrolyze ––> carbon foams (98% void volume)





averages of intensity data around azimuth -not on absolute scale

q–4



averages of intensity data around azimuth -not on absolute scale

q–4

sharp polymer/void interface



Plots of intensity differences from intensity averages over 22 positions


Plots of intensity differences from intensity averages over 22 positions

Plots repeat at 3 – 4 mm translation interval


Plots of sector averages of intensity vs translation position


Before pyrolysis

After pyrolysis


Observation in as-crystallized blend:

bands move when sample is rotated around growth direction

indicates rotation of crystal orientations

substantiated by high-angle x-ray studies

orthorhombic MA cells


Observation in as-crystallized blend:

bands move when sample is rotated around growth direction

indicates rotation of crystal orientations

substantiated by high-angle x-ray studies

band motion observed in pyrolyzed mat'l ––>anisotropic pore rotation

orthorhombic MA cells



pore shape assumed ellipsoidal



substantiated by oscillation in Porod data plots

pore shape assumed ellipsoidal


Porod constant, KP, for isotropic case

For anisotropic case

Also, for average chord length, <LV>, inside pore

vol. fact.







Shear-induced crystallization of polyethylene (see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced.

Documents

orientation slide

pyrolysis slide

polymers carbons observation

intensity averages

translation interval

void volume slide

sa smallangle

poreorientation periodicity