Heterogeneous Nucleation of a Semicrystalline Polymer on

Fiber Surfaces

Sangyeob Lee, Todd E Shupe, Leslie H. Groom, and Chung X Hse

ABatroct Nucleation phenomenon as aEkcted by the surface

conditions of six identical d n o n - w o o d fibers with three l d of fiber tnatm~nts were investigated by a d i n a t i o n of complementary tedad~ues. This study was based on results of a preliminary study on the influence of surface c-tics of thermo- ndmnical pulp (TMP) fibers on the tl.anocrjrstalline layer (TCL) gmwth and its codation with intmkhl stt.engtb ~ E S . Surface morphology of fiber ma- t d armd h- nucleation phemmenonon the fiber materid was carried out using scanning electmnk a d p c k b r light mi- copy. The nudeation e f 8 c k q was aramiaed in a

polymermetrixtodetefmineunityfadars(~),which directlyc~plabs~ibbsfreeenrrgyfnacarrelatlonof h v e o u s and ~lllcleation. The factor was gemmed from the crystafline deposit an- gle memmment on the fiber d c e during isother- mal cqstdhtion temperature at 140°& 0.1%. Both meammmmts indicate that of ex- tractedglradsurEaoewashedfibersi&slce~ induced h- nucleation of polypmpylene. Morphologid changes an the fiber surface were rp ported due to an elimination of relatively small parti- d e s ~ e g c h k v d o f s u r f a o e ~ t a n d f e w e r particles on the fiber surface indicated d d nu- cleation ability on the surfaa.

The ocameme of an e n d e d so- of nuclei confined on the w a d fiber surface is called crystalli- zation. Thtanr transcrystallization L used when nu- decrtion Mi is d d e m b l y high. A vast amount o f ~ h a s ~ ~ ~ ~ l d u c t e d o n ~ ~ ~ ~ a s p e c t s o f

in fiber-nidkd s@-e pdymerwmposites. Thestudies have focused onme- chanical popertics, which are affected by trans- apstaafnity molle than @ p w t h in the bulk (Sharpies 1966, Mullin 1993, Quillin 1993, Lin 1999,

Ebengou 1997, Hsiao 1990, Chang 1977). However, a detail nucleation mechantsm on the wood fiber sur- f a c e ~ ~ a n d ~ e n t @ ~ l a i n matezkl functhnalityonthebtafacisl phenomenon ofmatrixmaterials. M O U S ~ havepropased~~~lceptstoin-

crease the nucleation ability by rnadifying or control- ling the polymer matrix and surface ~ c t e r h t i i c s such as copolynm, additives, chemical composition, SLI&W roughness, and s d k e free en- (Gray 1974, Liu 1994, Wang 1996, Lee 2002). However, an i n a w d surface five energy was an d i k d y influ- enoe on nucleation ability to induce transcrystall- W o n on the fiber surEace because a transrrystalline ] a y ~ ~ ) w a s g e n & a n t h e f i b e r ~ ~ - kss of whether the surface free energy was changed by surface tmatments (WesterIlnd 1988, Hsho 1990, Mahlberg 1998). Wang (1 996) hd that a thicker TCL f o r m e d a t b i g h e r ~ ~ , andlargesresid- u a l ~ a t t h e ~ c e i n d i c a t e a n i m p m t a n t d e o f t h e l ~ e ~ ~ s t r e n g t h o f t h e ~ p o s i t e s c o r n - pated ta aydbzation at a lower temperahue. Ym (1999) faad that the nudeation density with addi- tion of MAPP ( d e i c anhydride polypmpylene) fnua l t o l O p ~ ~ e ~ t w a s ~ m n t l y ' xi, and a suf- ficient amaunt of nu&i on a single wood fiber in- ducedmmmyadbtion aroYnd the d fiber. The nudeation abili~y is also related to chemical contain- ment and m p h y of the fiber stmrfaoe during the - 0 ~ p r o c e s s O f ~ ~ p o f y m e r s O N a n g 19%). HOW-, a mnabual d h b ~ ~ a of cottonatrd~edwoodfibersez@yinducedtrans- qstdization when the surfkce was exposed (Gmy 1974). In the add-base theary, hydmgm baading is the

m a i n ~ o f b o n d i n g a t a p o ~ i n t e r f a c e w i t h hydmqlgmupricfiswFaces-Thetheoryisbased upon inkmdon emrgies that are dependat on the acidityofthehyQogendol.larandthe~ao- CepwI: Acid-base irm2m.i- cowsang in-on that imrolpes the sharing of an electron m, mcu- W y hydrogien h d i n g . In the case of celhrlostj the acid-base inMions can be descr3bed as pnedomi- namlyhydmgenbondingwithasurfacedominated by h y b x y l gmups. Interkid energy and intend bond (IB) rn-ts indicate a stmng correla- tion between the hydmxyl-rich (ad-) intdace and good adhesive properties (Jens~n 1978, Pizzi 1994). An i m m t applimtion of h t d x i a l acid- base bondiq is the pmdictable edum-t of inter- fadal bonding accomplished by surface conditions of

mterhls to enhance the in- add+ inter- actions (Fowkes 1987).

Attractive forces exist between any molecules when t h e i r ~ c e o f ~ t i o n i s c i a s e r t h a n ~ A (Chung 1991). The aUractive forces are usually insuf- fidmt for strong bonding when the molecules are small, but the amactive forces become strong when the mo1ecules are hqge. A classical theory of polymer nucleation is based on changes of the overdl excess free energy (AG) between small particles as a bdgn body and d c z y s ~ matrix Gibb free energy is also influenced by intimate m d h conuct, vol- ume of the matrk and size of the nucleus. H-, most of the nucleation is heterogc11~0us induced by foreign particles or the surface of materials rather than a spantandy induced nucleation known as homogenwws nucleatton (Mullin 1 993).

AG (Equation [ln is generaUy combined wlth two quantities of positive (surface k en- AGs) and negative (volume free -, AGv). The Gibbs h e energy at they, is Caned a critical free energy (AGm). Ho-, the heterqeneuus nucleation on the for- eign surface dif3h froln the homogemms nu& ation because ofdilkmcesin nucleus sizes (r~) . The difkences are also associated with the critical fkee energy (AGatr). Thcdb~e, h&mgermw nudeation has less unity than homogeneous nudeation and the unity factor can be expesed with a mmlation be- - two different nucleations.

The &tor &lily condates with iatafacial ten- sions at the bomdaries of aystabe depasit, amor- phous @on, and hdgn d c e . The &tact angle (@)~auyst&nedepositandawoodfikstw facecanbegeneratedtocal~theunityf&ctor. The baor e~uation is.

Theobjecdvesofthfs studywemto: 1. deterdm interaction mechanisinxs at nude-

aticznsitescausedbyfibersurfaoes,

2. inwstigate the eEkctiwmess of i n d hycb- phobidty of the fiber & on the m-

CPP) mat& sad 3, p l w v i d e ~ ~ ~ h t h e ~ t i t a t i v e n m e a s u r e

xnentsofnystaninedeposft~esdh/EIa- ti= oftheuystd deposit system onthe fiber Sulfate.

M a f e r l s a s w f a c e ~ ~ Atotal of six fibePrtrpes (8 barth-ail

pub DW1, *ed mchdcal pulp -1, mercial TMP, bleached K d t , unbl- Ki?rft, and carbon fibas) wtre usad to evaluate the influenceof sllrEaa morphokgy and hydrophobicity on the sur- facl? iIKhced h ~ e o u s n*ti011 phenome mm. Three difF-t fiber conditions (c~ntml, ex- tracted,andwatersaa%ed)wleseused~onwas pedbrmed with dichloromehne {CH2C12) on 8 bar TMP fibers, which wenu? pmhced from jwenile por- tions in a continuous, p m s d d , &&disc diner (80 p x d h n e r plate gap). The saxhlet extraczion was perf& in accudance with TAPPI staadard T 204 om-88 mppi 2004). All of the fiber mated& wexe washed out with distilled waterat roamtemperature ~ 2 4 h a u r s o f w a t e r s o a k i n g . T h e f i ~ ~ e x a m - ined for m i e c mocph01ogieal changes on the fiberanfaas chzetotheremoval ofexmaks a d extraneous matmids. The carbon and &aft fibers an^

~esofextmmesurfacecharacterist icsof~ paobicity and hydmphikity as well as changes in the irarrface 43Xmlical compositi~ll~.

Polypropylene (Escorene PD7292N E7, Exxon Mobil Chemical Ca.) was used lk the evaluation of hcterogenea~s nudeation phenome?wm at the inter- face of the fiber surface and the & a y d b e poly- merwithanisotbennaItem~of140"f O . l T .

I n m b s for madtorhagthe inhrhcial Phe-

ApoJarizinslightrni-pe(PLM)(McaDMLB 3Vll. -td with HCS302-STC200 c~ldlheat- ing stage) was used to dc- ' e the number of nu- clei, b/E ratios, and crystalliae deposit angles during the cqstdlbdon process when each polymer blend was @aced with the TMP fibers. The iso- PLM obsemation charadaized each txysbniza~on pI0- oess&tivetotheclifkmlt~characteristicsof the wood/non-WOOd fibas with PP. The PLM photo- micmgmphic images were provided h/E ratios and ~ ~ a n g l e s t o c a l c u l a ~ u n i t y ~ r ~ ( ~ ) on the Linear fiber d c e (F'ig. 1). A Spot RT digital camera (IXqpmak Instruments hc., Model #3,1,0 with 1600 by 1200 redut.ion) was used for deydop- i n g ~ a s a f u n c t i a n o f ~ n t i m . h - age-- Plus soham was used to conduct the image

and mnect ~uantitativc m ~ a t ~ of h/E ratios and drysrslIline deposit angles.

Moqholog id cbmaderM(s of the wood and mn-wood fibers w e investigated using a scarming e l m micamsap (SEM) (Hitachi S-3600N). Fi- bers, which were coated with a thin layer (ap- 15 mimme$em) of gold, observed in the SEM. The morphological C ~ C S d sutface conditions weax! Errwn phatomiicrogrpbic images with image -don conditions of 20 Kv aml1,JoOx.

Partide size d y s i s (PSA) was achieved using a particke size adyzer (Ro-Tap) and miaqpphic im- age atdysis to obtain quantitative particle distrlbu- tiom on the E b e r i w h c e s . The quandtative m- ment addnessed possible PP nucleatian caused by r e l a t i d y s m S r n ~ c l e s w t h e f i b e r ~ A c m - sizerm ?70A SISSyringe Injection Sampler with a widedynamicrmgesens~(LE400-05;covers0.5to 400pofparfideradius)wasusedtoanalyzeparti-

pisrnr 1. -(a) h4easu.m- mmtrs fbr nystaK'ne de- posit angles and lcttios of lam& deposit beween the j%er surface and the Mana;and (b) WEm- t i 0 0 6

Lee. Shum Graam. and H . s 4 93

Maet I.---- -

clesizcsontbeflh~.Numkofdd,pa~ ti c l e s h , a n 8 ~ ~ 0 f l ~ g e n e r a t e d f r P m P ~ a n d S E M h a g e s . ~ t i v e ~ t t t o n o f ~ mdeatbnanthe f iberwhce from 2 0 0 ~ mian- ~ a p h s a s a ~ o n o f u n i t ~ ~ w ~ d e f e r - mined with a mounted digital camera eqdpped with I m a g e - f r o P I u s ~ .

pulp ins^ Fiber

Snt~tes

w --

-.

ItisexpectedthatthefrIbaswlouldpussesshk s u r f a c e c h ~ ~ d u e t o t h e d o f e x - W v e s and extmtable materials from the surfaces mble 1). The carbon and Kraft f i b also plorvicEe extreme surface c h m ~ c s of hydmphobicity and h s ~ i t y with 1- RMP (6- bess pmdueed under the ligain gIass tmnsith point of 140°C) had lower extraaaMe mataials conqxmd totbeTMPfibers.Th~,therrewasnoligninrede-

- -

- - -

0 Washed

I - Llnear (Control) - - ~ ' - - Unear (Washed) ;

posit after the defi-on pmcess with the RMP fi- b e r : A h i g b r ~ ~ a f t a r t h e p r o c e s s w a s *noted.

Unf ty -~+~~from- tQys ta l l lne augksandQystaniaedepositrati~bgsedonPLM ~ o n s a r e s h o w n i n ~ 2 . T h e s u r L a c e m o r - phology and &mishy influenced crystal impurities of fibers and pmdded a better nucleation site to the PP ma* arsd uhe AG- di&emxs of the fiber sur- face amtribute the nucleation ability of Pl? The SEM andPLM results cmdatedtotheunity factorusinga method of tabular and numerical comparisons among the fibers. The d t also shows what k i d of wood fiber s u r k c pmpertics an efktive for induc- ing hetangenems nucleation and how surface prop erties idhence the purity changes of A',, on the wood/norl-woadsurfacecom~tothebul l t~ Some degree of material hycbphoMcrty on the fiber

Aopert6eo 17% 1637: %to795 9996 na tiaa

>99.5% czwbon - alluloa?

hldstmc~~~tent 5.646 10.5% 5 -6% 52% 11.8% -0,03% +

3.2% 3.9% _ L z 3 1296 - - . . . . - -- 0.78%

-Linear (Extracted)]

I I T M -- --- --

Zoltek C o m ~ . I n c .

TbamoIMhmieal l b f i

UKP I BKP ~ h r m l o c k

O h F ~ )

PadaachCa lmMimILIb

8 h t J ~ N I ~ Y pine (Pinrutadz)

BCCUW

M e

IMP na

InlandEmpin Pawco.

Cm TMP -pine

~ ~ p o ~ ) ~ h c m l o c k

(mwhdaopkyao) Westmawhitepine (Pinus fmnrida)

Plum Cnek MDF, Inc.

(e) washed fibers

Ffgurr? 3. - Hi?taogenww nuci?aaiim phenomenon a s s ~ t e d with the surface minpholqy due to the fiber treafments.

surfacewlllbebendlcidinthelamelladepositsys- tern on a fiber surhce and create an intimate contact systembetweentheflbersurfaceandPP.Thismecha- nism should be addressed in a of sect a n b y kmxs (i.e., the role oE the van der Walls faces). Sutfaa h-obicity of the fiber materials plays a bendkid rale on the lamella orientation on the fiber surface

Figam 3 shows heterogeneous &tion phe- ~ n o n ~ w i t h s u r f a c e m o r p h o l o g y d u e t o the k lerels of fiber conditioning. The Themiar*.

W@-dd==hmorpSldogicalchengesamong the fiber ma- with each surface tmatmenL The extraction of the sllrface did not i dhend PP nude+ &nontheexbrzbctedf3bersuthces.SurEac#uaclts a n d ~ c l e s s t i I l ~ o n t h e I v u g h m f a c e o f eKtractedfibers.However,thewsshed~&ow- ed an extreme reduction in the he^^ nude- ation. The surface showed surface checks but s clean morphalogy and less particles. Surface mughnes could afFect the fiberlrnatrix adhesion and the nucle-

ation ability of semiaystabe polymers (Cai 1997). However, the surFace roslgfuless and checks probably did not m-nd directly to PP nucleation. FQure 3 also Wcates that water isolated mate%& from the flber slnface phys an impartant role in the PP nude a t i o n w i t h s u r h c e ~ c s o f c h e m i d ~ &tiom and surfaa free energy.

Figrtne 4 shows partides loc8ted on the fiber sur- face to iaduce heterogseneous nucleation. Particles of variabessizescanbeseenontbe~eofthewaod fibers. Most of the particles am latad on surFace checks a d damaged smfaces. The particles had reIa- tively smooth and d imzpholagy. Based on the nucleation theoq, mnopth and mmd surfnea F vided lower md&ce area, wbich influences Gibbs fme energy,asascomparedtoroughsurEaoesduetotheex- pocPedsurfaceareatothcmobPP. The functionof su~face &ah d roughness may be a natural hold- ing device for &tidy small particles to induce the PP nucleation.

(a) conttol fibers (b) (4

Figure 4. Partictes on the @wr swfi4a to induce nucteaiSon.

(right) numbsrofluac~on the fibasurfhaa

Figune 5 shows both particle distribution and 4hiwlasri0~ ~herofnucleionthe£ibersurfaa.Woodfibem produced using the mechanical p u l w alsa show the h i m nudeation ability among the tkmedi&reartpressure~tio~ls.Tbemedian~ theparticIe~tionsofeachfibertppeswas0.64 pm, emqtfbrR.MP (2.68 pm). Relativdy d e r p a r - tides (~0.Jp)onthefiberswfacecanbeimportant for the h- nucleation af PP, Ho\kanrer, the V limitattion of a wide dynamic ~.ange sen- sor, which covem 0.5 to 400 pn of particle radius, in- dicated further investigation with particle sizes d a t h a n 0 . 5 pm. Anavemgedus ofnwleuswas 0.64 &m and the n d d radius is much s d e r than nucl-.

The objectives of this study vme to determine in- tcaacth mechanbms at nucleation sites caused by f i b e s ~ , h e s t @ t e t h e ~ ~ e s s o f i n a e a s - ed~bicityofthefibersurfaceonthePPma- trix,andprovidefactarsfmmthe~uand~mea- ~ t s o f Q y s t a l l i n e ~ t a n g E e s a n d b / E w b o f ~ c r y s t a l ~ i t s y s t e m o n ~ f i k s l u f a c e . Based on the mdts of this study, the following con- clusions can be c h ~ ~

1. raugh surfaces serve as a natural particle Wd- ing device,

2. smooth and hydmphobic surfaces pawide a beneficid rde for crystalHnte deposit,

3 .par t idesanddat tnsdaMehtheB- k ~ & a n ~ t I P l e i n ~ neolls nucleation d rrystalline degosit, and

4. isolated materids from t l ~ fiber surface en- material impurity of the fibers and m t e polymmnucleatian sites.

G a i Y . , J . ~ a n d H . W t t i e h 1997.7hmyA- "' -' ia-isatrscticj&pq&mearmpoJitwiua

g d h t . 3. AppL PolymeP Sd. 65: 71-74. c % € q , E P . I m . ~ - l r t u c t i e s o ~ ~ * w. J. AppL Pb&mer Sci. 21 937-942.

t%mg,F.EL 1 9 9 l . U n i $ e d t l s s o r y a n d ~ 0 ~ ~ J . A@ W S d . 42:1319-1331.

Ebmgnu, R.H. 1997. Admqthn as a mechanism fix nucleat- ingaanitr:Ath--on. J.PolymerS& Part B: Polymer P~@cs 35(9)$3 333-1338.

Pawires ,F~ 1987.Role6fdkintaEacislkwdingind besi011.J. Adh. sci. ' J k h 1(1):7-26.

Gray, D.G. 1974. Polypqqkw ra the -- r s o e o f ~ f i ' b e r s . P d y m e r ~ e d i t i o a n 5 1 0 - 5 1 4 .

Haiao,B.S. E.J.H. Cbea. 1990.-imqhses in advanced polymer composites. Cumroiled Intaphues in Composite IHmriab, H. Ishida, Ed. Elseviet pp. 61-22.

WB. 1978. The Lewis acid-basedefinitions: A status- port. Chem. Reviews ACS. 78(1)77&784.

Lee, S-Y- 2002. aansaystalliPltion behadm and inadkid ~ofaJemicrystaltiaepolymercombinedwith thermomschaaicapatp~)fiber:M.S,Thesis.~43f Idaho* Maiscow, ,ID. 72 p.

Liu, M E Wokus&, D J. d E G . Rials. 1%. C k - ~ 0 n o f t h e ~ b e t w e m a 4 h d ~ c f i b a s a n d a tbermdplastic matrix. Composite Intdace. 2(5):419-432

~ R , H . E - M . ~ l ? D e n s r . a a d R M . R o w d l . 1998, E l i e c t d ~ a a d k ~ ~ l d i s i l ~ ~ o n ~ l h a r - ~ I ~ t y a n d ~ m ~ e s o f p o + q y - l e n e d l i g n m J. A d k Adbes. 18283-297.

Mullin, J.W. 1993. CrystaUization, 3 d ed. Buttexworth- Hdrrslnsnn Ltd. pp. 172-189.

Ph&A 1 9 9 4 . ~ d ~ t e c h o o d o g y . N h d De4hr Inc. New YorL pp. 2-14.

QdEn. D.T. DX. Cdfk ld , and JA. Knrtsky. 1993. Cryaall- initp in tbe system 0. Nucleation d ~ m o r p h o ~ 3. Agpl Polymer Sd. 50(7): 1187-1194.

Sherphs,A. 1 9 6 4 , ~ m t O p o l y m e r ~ E d - ~ ~ r m ~ m ~ o a d o n . 2 1 pp.

Thppi. 1988.Th&t&methodTZdi0m-88Sohrmt~ Qf~adpulpP'EgppiAt]anta .GA.

Wag, G. and LR Harrisosl. 1994. Study of the pdemntial ~ o f ~ o n t h e s u r f a o e o f ~ f i - bas.In:Roc.oftbe52ndAnrmalTech. Conf.ABlTEC94. hrt 2. gp. 1474-1475.

~~angC.and~M.Hwang. 199tL-kPI'PE P i b e d P P ~ ( I ) a y s t a n i z a b l o n ~ a n d ~ phologp.1. Pdymer §ci.: Part B: Pdymer Pirysics. W.47-56.

Wang,C. andL.M. Hwang. 1996.-mof FIFE iibet.Ippcom~tes@).~oftranscrystaliinityonthe interhd stmngth J. Pdymer Sci. Part B: Pofymer Physics. 34~1435-1442.

SB. aod3.C. Bbl& 1988. SU&CX -dm- t m a t e d d ~ c e l M o s e f i b e n r . J.Appl. Poly- mer Sci 345(3)523-534.

Yia, S, TG. Rials, d hkl? W b b t t 1999. C a y d b t k n be- ba*ofpdgpkaWZmealldits~onwoadfibercom- pogitepropatieghr:Proc.dtht5thInternationalComf.on W&ber--Plamic Composites. Foopst Products Society, hkkm, WI. pp 139-145.

Recent Developments in Wood Composites

Edited by Todd E Shupe -

Forest M u d s Sodety 2801 M a d d l Court

Madison, WI 53705-2295 phone: 608-23 1-1 361

fax: 608-231-2192 www.foresQmd.org

Opthizing Natural Fiber-Rehfbrced Polymer Composites Through -end Design

by Rupert Wmmq Andrea G- GUwer Wuzella, and RudoEfh3sskr.. . . . 73

Characterizing Wet-Process Hardboard Manufacture by the Use of Expahental Design by Th&mas Hutter, Rupert Wmmet; and Rudolfkskr . . . . . . . 8 1

Wmgenmus Nucleation of a Semiuystalline Polymer on Rber Surfaces by Sangyeob Lee, Todd E Shupe, Leslie H. G m m , urui Chtcrtg K Hse . . . .