On the growth rate of spherulites and axialites from the melt in polyethylene fractions: Regime I and regime II crystallization

Abstract

Th e growth rate C of th e cr ys tallin e bodi es a pp ea rin g in eac h of a se t of 35 c haracte rize d po ly. e th ylen e fracti ons ra ngin g from 3600 to 807 ,000 in molec ular we ight ha s been meas ured as a fun ction of th e unde rcoolin g tJ.T. In isoth e rmal c rys tallization, only ax ial ites we re found from M",= 3600 to 18 ,000.(For th ese run s, tJ.T < 17.5 °C.) From M".= 18 ,000 to M". "" 115,000 coa rse·grain ed non ·band e d s phe ru · lit es we re fo und for tJ.T > 17. 5 °C , and axialites for tJ.T < 17.5 °C : a rathe r s ha rp brea k occ urre d in th e log .o C ve r sus T data at tJ.T "" 17.5 0c. Th e morphologi ca l changes we re more gradual. Above Mil' "" 115,-000, only nea rly s tru ctureless " irregular" s ph erulit es we re found a t all und e rcoolin gs corres pondin g to isothermal growth. Typica l rin ged sphe rulites were o btain ed only on quenching. Wid e·a ng le x·ray data s howed that th e usu al orthorhombi c subce ll predominat ed in all th e morph ologies e ncount e re d. Lo w· angle x·ray data showed tha t th e s pec ime ns ex hibit e d lam e llar crystallization irres pectiv e of th e particular gross morphology involv ed. Th e growth rat e data on eac h fra c tion we re analyzed us in g /T (tJ.T )/]where / "" I to obtain va lu es of K" a nd Co. Th e va lue of Y in K,,= Ybuue/ (tJ.hj )k was obta ined fo r eac h morphology by a ppl ying th e "Z" test of La uritze n. Y = 4 for regim e I cr ys talli zation (s in gle s urface nucl eus leads to co mpl etio n of s ubs trat e) and Y =2 for regim e II cr ys talli za tio n (num e rous s urface nu c lei involve d in s ubstra te co mp letion). It wa s found that the axia lites obeyed regim e I kin e tics (Y=4), th e coarse·grain e d s phe rulit es regime II kin etics (Y = 2), and th e irregular s ph e r ulit es " mix e d " kineti cs (Y -3). Th e ass umpti on that th e sub strat e le ngth L in Laurit ze n's regim e theory was -5 I'-m led to the prediction of a rath e r s harp regim e 1 ..... regime II tran sition (corresponding to a break in the 10glO C versus T dat a) a t tJ.T "" 17 .5 °C, in accord with ex pe riment. Th e UUe value ca lc ulat ed fro m K" and Y for M". ;;. 20 ,000 was ap proxim ate ly co nst a nt with molec ular we ight and indep end e nt of morphology; th e limiting value of uU e from kineti c meas ure me nt s was about 1285 e rg'/c m 4 • corre· s ponding to Ue(x)=90.5 erg/e m ' and u= 14.2 erg/c m ' . (This valu e of Ut'{x) co mpare s favorably with u dcQ)= 93 ± 8 e rg/ cm ' from me ltin g point expe riment s.) T he in c rease of uUe and U e that too k place at low mol ec ul ar we ight s on up to -20 ,000 was treat e d usin g an expression given by Hoffman , viz , Ue=Udx) [(,.,+/3;) / (,.,+1)] where v=number of fo ld s per molecule, /3; = U"c;lIum)/Ud x) , I ntermittent hi gh and low values of U e were found ex p erim entally in thi s regio n , s howin g that j3 ; varied with in creas· in g mol ec ular we ight between 0.15 and -0.7. Theore tic al estimates of these upper and lowe r bound s for /3; are give n . Th e ...

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

“…6), and theoretical 7,8 and experimental [8][9][10][11] verification of regular chain folding in both homopolymers and copolymers (with low comonomer incorporation) rationalized by the HL theory, this theory was dominant for the next 40 years. No serious rival for the explanation of flexible chain polymer crystallization was entertained as alternatives to the (secondary) surface nucleation theory.…”

Fabrication of Hollow Silica Particles Using a Self-Assembled Polyethylene Granule as a Template

“…Acid Value of PE Wax. Even though the morphology of single lamella has been extensively studied from the dilute solution and the melt [31,32], self-assembly of PE wax having broad molecular weight distribution from a nondilute solution has been rarely studied, in particular, not for partially oxidized PE wax. The oxidation degree of PE wax can be defined by acid value where PE wax possesses oxygencontaining functional groups such as carboxyl, hydroxyl, and carbonyl, expecting reduction in crystallinity of selfassembled structures.…”

“…Spherulite structure with few tens micron in size can be obtained from its melt state by a cooling process which originated from stacking of lamellae with interlamellar thickness of~12 nm [31]. Single lamella was obtained from cooling of hot and dilute PE in various solvents [32].…”

A Review on Polymer Crystallization Theories

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