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m odyfikow ane bydroksyzw iązki jako składnik n a n o k o m p o z y tó w 15

S. K um ar* a n d C K D as*

Stearate modification of Layered Double Hydroxide (LDH) for Polyurethane Elastomeric Nanocomposites

Layered Double Hydroxide (LDH) is a class of inorganic clay materials having layered structure in which anions are accommodated between the positively charged metal hydroxide layers. An increasing interest exists, because this class of materials can be used as catalysts, photo catalysts, catalysts sup­

ports, anion exchangers and as nanofillers in polymer composites, etc. LDHs with easily exchangeable interlayer ionic species have tremendous potential as novel fillers for polymers composites. Due to a low interlayer space and hydrophilic nature they hardly disperse in polymer matrices. After suitable modifi­

cation by anions, LDHs can be successfully dispersed at nanoscale in a wide range o f polymers. LDHs as a nanofillers improve the flame retardancy and barrier properties of polymer composites. In the present work Mg/Al based LDH was modified by the regeneration method. Modified LDH samples were charac­

terized by XRD, FTIR, HRTEM, SEM and FESEM. XRD results indicate that anionic moiety was intro­

duced into the gallery space and acts as pillar increasing the gallery height, what is evident by increased interlayer spacing. FTIR studies o f modified LDH samples corroborated the presence of anionic moiety.

From FESEM study it was observed, that after modification of LDH, platelet morphology is completely different from that, which was recorded for pure LDH with hexagonal structure. This modified LDH is well exfoliated in polyurethane polymer matrix with improved mechanical properties.

Key words: Layered Double Hydroxide, Regeneration method

Modyfikacja dwuwarstwowych hydroksyzwiązków stearynianem w celu zastosowania w elastomerowych nanokompozytach ureta- nowych

Dwuwarstwowe hydroksyzwiązki (LDH) stanowią grupę nieorganicznych materiałów mineralnych, w których aniony umiejscowione są pomiędzy dodatnio naładowanymi warstwami wodorotlenków metali.

Zainteresowanie tymi zw iązkam i ciągle wzrasta, ponieważ mogą być one stosowane jako katalizatory lub ich nośniki, fotokatalizatory, wymienniki jonowe oraz jako nanonapełniacze w kompozytach poli­

merowych. LDH, ze względu na łatwość wymiany jonów w warstwie pośredniej, ma ogromny potencjał jako nowy napełniacz kompozytów polimerowych. Jednak ze względu na niewielkie odległości między warstwami i hydrofilową naturę trudno jest zdyspergować je w ośrodku polimerowym. Jest to możliwe dopiero po odpowiedniej modyfikacji i wymianie anionów w warstwie pośredniej.

LDH jako nanonapełniacze zwiększają odporność kompozytów polimerowych na palenie i poprawiają ich właściwości barierowe.

W niniejszym artykule omówiono wyniki modyfikacji LDH, opartego na związkach magnezu i glinu, z wykorzystaniem metody regeneracji.

Zmodyfikowane hydr oksy zw iązki scharakteryzowano wykorzystując analizę XRD, FTIR, HRTEM, SEM i FESEM. Wyniki dyfrakcji rentgenowskiej (XRD) wskazują, że nastąpiła wymiana anionowych fragmentów struktury, a nowo wprowadzone ugrupowania rozpychają warstwy metaliczne, o czym do­

wodnie świadczy zwiększenie przestrzeni między warstw owej. Analiza widm FTIR potwierdziła obec­

ność nowych ugrupowań. Na podstawie badań FESEM stwierdzono, że po modyfikacji całkowicie zmieniła się morfologia LDH.

Modyfikowane hydr oksy zw iązki były dobrze eksfoliowane w matrycy poliuretanowej, co skutkowało poprawą właściwości mechanicznych kompozytów.

Słow a kluczowe: dwuwarstwowe hydr oksy związki, metoda regeneracji

I. Introduction ______

*Materials Science Centre, Indian Institute of Technology, Kharag-

Layered Double Hydroxides (LDH) are a new type of pur-721302, INDIA

nanofillers [1]. LDHs are anionic clays comprising posi- * Corresponding author. Tel: +91-3222-283978; Fax: + 91-3222-

tively charged layers with anions and water molecules -282700/255303, E-mail address: chapall2@yahoo.co.in

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m odyfikow ane hydroksyzw iązki jako składnik n a n o ko rn p o zytó w 1 6

in te r c a la te d in th e in te r la y e r r e g io n . T h e g e n e r a l fo r m u la o f L D H is [M 111.XM I11X (O H )2]x+(An')x/n Y H 2Q W h e r e , M 11 is d iv a le n t m e ta l s u c h a s C a 2+’ M g 2+> Z n 2+ etc., M 111 is tr iv a le n t m e ta l s u c h a s A l3+, C o 3+, Cr3+ etc., A N' is a n a n io n s u c h as O ' , C 0 32", N 0 3~ e tc. X is g iv e n b y M ffl/ M II+ M ni a n d its v a lu e v a r ie s fr o m 0 . 2 5 to 0 .3 3 [2].

S tr u c tu r e o f L D H s c a n b e e x p la in e d a n a lo g ic a lly to b r u c ite in w h ic h is o m o r p h o u s r e p la c e m e n t o f d iv a le n t c a tio n b y triv a len t o n e g e n e r a te s p o s itiv e ch a rg e o n m e ta l h y d r o x id e lay ers, w h ic h is c o m p e n s a t e d b y n e g a ­ tive ch a rg e o f in terla y er s p a c e o c c u p ie d b y a n io n s [3, 4 , 5 ]. I d e a liz e d stru ctu re o f L D H is g iv e n in F ig u r e 1. L a­

y e r e d d o u b le h y d r o x id e s c a n b e u s e d in w id e r a n g e o f a p p lic a tio n s a s ca ta ly sts, p h o to c a ta ly sts , c a ta ly s t’s s u p ­ p o r ts , a n io n e x c h a n g e r s , c o n t r o l l e d d r u g d e liv e r y s y s te m s etc. [6, 7 , 8 , 9 ,1 0 ] .

L D H s w ith e a s ily e x c h a n g e a b le in te r la y e r io n ic s p e ­ c ie s h a v e a ls o tr e m e n d o u s p o te n t ia l a s n o v e l n a n o fille r fo r p o ly m e r s c o m p o s ite s [5]. B u t to a c h ie v e th e g o o d p ro ­ p e r tie s p a r tic le s o f th e fille r m u s t b e h o m o g e n e o u s ly d is ­ p e r s e d in to th e p o ly m e r m a tr ix . T h e m a in p r o b le m in p r e p a r a tio n o f th e p o ly m e r n a n o c o m p o s it e s is, th e L D H s la y e r s are c lo s e ly s p a c e d a n d it is v ery d iffic u lt fo r th e p o ly m e r to p e n e tr a te th e g a lle r y d u r in g m ix in g . L D H s c a n b e s u c c e s s f u lly d is p e r s e d a t n a n o s c a le in a w id e r a n g e o f p o ly m e r m a tr ic e s o n ly a fer s u ita b le m o d ific a ­ tio n . V ario u s m e t h o d s a re u s e d in o r d e r to a c h ie v e th e a im s u c h as, in-situ s y n t h e s is , io n e x c h a n g e , r e g e n e r a ­ tio n a n d th e r m a l r e a c tio n s [1 1 ].

L D H a s a n a n o f i l l e r im p r o v e t h e f l a m e r e t a r d i n g p r o p e r t i e s a n d b a r r ie r p r o p e r t i e s o f p o ly m e r c o m ­ p o s i t e s . D u e to t h e d i r e c t i n t e r c a l a t i o n o f L D H is l i m i t e d , t h e r e a r e s e v e r a l m e t h o d s to i n c o r p o r a t e t h e p o ly m e r a t t h e c o r e o f h o s t m a t e r i a l , w h i c h a r e a s f o l lo w s :

# in t e r c a la t io n o f th e m o n o m e r m o le c u le s w ith s u b ­ s e q u e n t p o ly m e r iz a t io n [1 2 , 1 3 , 1 4 ],

# in c o r p o r a tio n o f lo n g c h a in m o le c u le s c o n ta in in g a n io n ic f u n c t io n a l g r o u p s in to th e g a lle r y w h ic h in ­ c r e a s e s p a c e s b e t w e e n L D H p la te le ts , th e r e fo r e p o ly ­ m e r c h a in s c a n b e e a s ily in t r o d u c e d b e tw e e n th e m , w h a t r e s u lt s in b e tt e r d is p e r s io n [1 5 , 1 6 , 1 7 , 1 8 ]. In th e p r e s e n t w o r k M g /A l b a s e d L D H (H y c ite 7 1 3 ) w a s m o d if ie d w it h s o d iu m s te a r a te b y r e g e n e r a tio n m e th o d .

2. Experimentation and Measurements

2

.

1

.

Materials used

M g /A l L D H (H y c ite 7 1 3 ) s u p p lie d b y S iid -C h e m ie A G G e r m a n y

# s o d iu m ste a r a te s u p p lie d b y K e m p h a s o l M u m b a i, In d ia.

p o ly u r e th a n e e la s t o m e r (U r e p a n 6 0 0 ) s u p p lie d b y R h e in C h e m ie G erm a n y .

s t a n d a r d is o c y a n a t e c u r a tiv e s u p p lie d b y R h e in C h e m ie G erm a n y .

2.2. Modification of LDH

C o m m e r c ia lly a v a ila b le L D H (H y c ite 7 1 3 ) w a s m o ­ d if ie d b y r e g e n e r a tio n r o u te. In th is m e th o d , o n e g ra m o f L D H w a s c a lc in e d in a m u f fle fu r n a c e a t 5 0 0 °C w ith h e a tin g ra te o f 5 ° C /m in fo r th r e e h o u r s a n d th e n it w a s c o o le d d o w n to 3 5 ° C T h is c a lc in e d L D H w a s a d d e d to a q u e o u s s o lu t io n o f s o d i u m s te a r a te u n d e r v ig o r o u s stir­

rin g fo r 2 4 h o u r s. D u r in g m o d ific a t io n p r o c e s s te m p e r a ­ tu r e w a s k e p t c o n s t a n t a t 6 0 °C to m a in ta in th e s o lu b i­

lity o f su r f a c ta n t m o l e c u le s in w ater. M o d if ie d L D H w a s s e p a r a t e d fr o m t h e s o l u t io n b y f iltr a t io n a n d s u b ­ s e q u e n t ly w a s w a s h e d th r e e tim e s w it h h o t w a te r a n d d r ie d a t 6 0 °C fo r 4 h o u r s in a n o v en . M o d if ie d L D H s w e r e m a r k e d a s S L D H .

2.3. Preparation of LDH and Polyurethane nanocomposites

N a n o c o m p o s it e w a s p r e p a r e d b y u s in g th e fo llo w in g m e th o d : 3 g o f p o ly u r e t h a n e w e r e d is s o lv e d in 2 5 0 m l o f te tr a h y d r o fu r a n , in n e x t ste p 1 g o f m o d ifie d L D H w a s a d d e d s lo w ly to th e s o lu t io n u n d e r v ig o r o u s stirrin g;

a fte r w a r d s th e c o m p le t e s y s t e m w a s stir r e d w ith c o n ­ s t a n t s p e e d fo r 4 h o u r s . F in a lly , s o lv e n t w a s e v a p o ra ted a n d r e s id u e r e c e iv e d w a s m ix e d w ith 3 0 g o f p o ly u r e ­ th a n e in h a a k e -t y p e in t e r n a l m ix e r w ith ro to rs s p e e d o f 3 0 r p m a t r o o m te m p e r a tu r e . In th e la s t p h a s e o f m ix in g a p p ro p ria te a m o u n t o f c u r a tiv e w a s a d d e d . E la s to m e r ic c o m p o s it e s w e r e v u l c a n i z e d u n d e r c o m p r e s s io n a t 1 0 M P a p r e s s u r e a t 1 7 0 ° C

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m odyfikow ane bydroksyzw iązki jako składnik n a n o k o m p o z y tó w 1 7

2.4- Characterization of pure, modified LDHs and their nanocomposites

2.4.1. TG A Study

Thermogravimetric (TGA) analysis of the modified LDHs was earned out using a Dupont TGA-2100 ther­

mal analyzer in air in the temperature range from 50 °C to 600 °C, with a heating rate of 10 °C/min.

2.4.2. X-ray Diffraction Analysis

X-ray diffraction measurements were recorded on Rigaku Miniflex diffractometer equipped with Cu-Ka radiation with scanning rate of 20°C/min between 2.0°

to 14.0°, chart speed of 10 m m/20, range of 5000 c/s, and a slit of 0.2 mm, operating at a voltage of 40 KV, cur­

rent 20 mA. Interlayer spacing was calculated using Bragg’s equation nA, = 2dSin0. W here X is the wave­

length of X-ray, 0 is the glancing angle of incidence and d is the interlayer spacing of LDH layers. XRD spectra were interpreted with respect to the position of the first order basal reflection <003>, which depends on the dis­

tance between two adjacent metal hydroxide sheets in the LDH crystal lattice (i.e. d).

2.4.3. HRTEM Study

Morphology of the composites was observed in high resolution transmission electron microscope (HRTEM, JEOL 2100). For the HRTEM observation, ultra-thin cross-sections of specimens were prepared by using Leica Ultra cut UCT ultramicrotome.

2.4.4. FTIR Analysis

FTIR analysis was carried out to check the changes in the modified LDHs samples and their composites. It was performed from 550 cm '1 to 4000 cm '1 using Thermo- nicolet/Nexus 870 FTIR spectrometer. The powdered samples were mixed with KBR in a 1:200 ratio of their weight and pressed in the form of pellets for measure­

ment. For measuring FTIR of the polymeric composites thin films of thickness in the range 100-250 pm were compression molded.

2.4.5. Mechanical properties study

Mechanical properties were determined by means of universal tensile testing machine (Hounsfield H 10KS) under ambient conditions. The moduli at 100% and 300% elongation, tensile strength and elongation at break were measured at room temperature. The initial length of specimen was 25 mm and the speed of jaw separation was 500 mm/min.

2.4.6. FESEM and SEM Study

SEM s tu d y w as c a r r i e d o u t in VEGA TESCAN//LSU. The tensile-fractured samples were coated with thin Gold. D uring scanning Vacuum was in the order of 1 0 '4 mm Hg to 1 0 '6 mm Hg during the scanning.

FESEM analysis was perform ed using a Carl Zeiss-SUPRATM 40. The fillers were coated with a thin layer of gold (approximately 5 nm). Vacuum was in the order of 10"4-10'6 mm Hg during the scanning of the samples.

3. Results and Discussion

3.1. Thermagravimetric analysis (TGA)

The thermal analysis of the modified LDH was pri­

marily aimed to investigate behavior of the organic frac­

tion and also the metal hydroxide layers during decom­

position. This was carried out by identifying particular decomposition stages and the temperature ranges corre­

sponding to them on the TGA plots. The comparison of the TGA plots of the modified LDH with that of the un­

modified one gives an indication how the interlayer anio­

nic moiety influence the decomposition of the host mate­

rial. TGA plot of unmodified LDH and SLDH are shown in Figure 2. The unmodified LDH shows two-stage de­

composition process: a low temperature (up to about 225°C) dehydration stage due to the loss of interlayer

water and a high tem perature decomposition (225- 500°C) stage due to the loss of interlayer carbonate and dehydroxylation of the metal hydroxide layers.

Stearate modification of the LDH changes signifi­

cantly its thermal decomposition behavior in compari­

son to the unmodified LDH, especially the second stage of the decomposition process, which results complete collapse of materials structure.

The loss of interlayer water molecules up to tempera­

ture about 225°C in the modified sample SLDH is less compared to unmodified LDH, this indicates that in SLDH less num ber of water molecules is accommo­

dated in the interlayer region.

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m odyfikow ane b y lro k s y z w ią z k i jako składnik n a n o k o m p o z y tó w

18

The second decomposition stage is also changed sig­

nificantly after organic modification. The major weight loss in case of SLDH is caused by the decomposition of the interlayer anionic moiety However, major dehydro- xylation process of the host materials starts around 300°C

Fig. 3. TGA plot for PU and PUSLDH

Rys. 3. Wykres TGA czystego poliuretanu (PU) i poliure­

tanu zawierającego modyfikowany hydroksyzwiązek (PUSLDH)

TGA analysis of the pure PU and PU/LDH nanocom­

posite is shown in Figure 3. Thermal degradation PU is mainly caused by depolymerization, which begins from 190 to 250°C due to the failure of urethane links, releas­

ing the polyester and isocyanate (monomers) used in synthesis of PU chains. The monomers slowly volatilize during the continuous heating process. The complete volatilization of the resulting chain fragments is avoided by the dimerization of isocyanate to carbodiimides, which react with the alcohol groups to give relatively stable substituted urea’s. The decomposition in the third step begins from 300 to 400°C, which is related to the decomposition of urea groups and corresponds to the high temperature degradation of these stabilized struc­

tures to yield small quantity of carbonaceous char. Pre­

sence of LDH causes distinct changes in the thermal de­

composition behavior in comparison to the unfilled poly­

urethane. With the addition of 3 wt % LDH, the first de­

composition stage in unfilled polyurethane is not only shifted to a higher temperature range, but also the extent of weight loss during this stage decreases.

3.2. XRD Analysis

XRD re su lts of unm odified LDH, SLDH and PU/SLDH composite from 2 to 14° range are shown in Figure 4. As expected, the position of the first order basal reflection <003> in SLDH is shifted to a lower 20 value indicating intercalation of anionic moiety in the

Fig. 4. XRD plots of LDH, SLDH, SS (Sodium Stearate) and PUSLDH

Rys. 4. Dyfraktogramy XRD uzyskane dla dwuwarstwo­

wego hydr oksy zw iązku (LDH), stearynianu sodu (SS), hydr oksy w iązku modyfikowanego stearynianem (SLDH) i poliuretanu zawierającego modyfikowany stearynia­

nem hydr oksy związek (PUSLDH)

gallery space. SLDH sample does not show distinct re­

flection at d = 0.76 nm. Intensity of peak in modified LDHs also decreases which indicates that modification leads to low crystalline LDH. Shifting of <003> peak to the lower 20 value suggests that anionic moiety has gone inside the LDH layers and increases the interlayer gap to 2.75 nm. In case of PU/SLDH nanocomposite contain­

ing 3 wt % of SLDH no peak has been observed. This is suggests that the organically modified Mg-Al LDH la­

yers are partially or completely exfoliated in PU matrix.

XRD provides a partial picture about the distribution of nanofiller and disappearance of peak corresponding to d-spacing does not always confirm the exfoliation of filler in polymer matrix. XRD is unable to detect regular stacking exceeding 8.8 nm. Hence, a complete charac­

terization of nanocom posites morphology requires microscopic investigation in these case.

3.3. HRTEM Study

Figure 5 shows the TEM images of PU/SLDH and PU/LDH nanocomposites with 3 wt % of LDHs. The dark lines represent the LDH layers, whereas the bright area represents PU matrix. It is also evident from the TEM image that the SLDH layers are dispersed partially in a disordered fashion in the polymer matrix. In case of PU/SLDH layers dimensions are less, which is also sup­

ported by FESEM study, and the layers are randomly distributed in polyurethane m atrix in the case of PU/LDH nanocom posites layers are agglomerated.

HRTEM study also correlates with the improvement in mechanical properties. Better dispersion results better mechanical properties.

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m odyfikow ane b y lro k s y z w ią z k i jako składnik n a n o k o m p o z y tó w 1 9

Fig. 5. HRTEM images ofPUSLDH (A) and PU/Unmodi- fied LDH (B) nano composites

Rys. 5. Obrazy HRTEM nanokompozytów poliuretano­

wych zawierających modyfikowany stearynianem (A) i niemodyfikowany dwuwarstwowy hydroksywiązek (B)

Fig. 6. FTIR spectra ofLD H and SLDH

Rys. 6. Widma FTIR zarejestrowane dla LDH i SLDH

3.4. FTIR Analysis

The FTIR spectra of the unmodified and modified LDH are shown in Figure 6 Modified SLDH shows two types of bands: the first one corresponding to the anionic species intercalated between the host LDHs layers and the second corresponding to host LDH materials. This has been shown in details in Figure 6 and Table 1.

Table 1. FTIR frequencies o f LDH, SLDH, PU and PUSLDH

Tabela 1. Zakresy częstotliwości widma FTIR istotne przy analizie próbek LDH, SLDH, PU i PISLDH

Materials Band Positions

(c m 1) Types of Vibrations 3420-3470 -OH Stretching LDH 1356 CO32', C-0 Stretching

550-750 M -0 Stretching

SLDH

2849 & 2917 C-H Symmetric and Asymmetric Stretching.

1558 Asymmetric -COO' stretching

1472 CH2 bending

PU 3330 Urethane N-H stretching

1728 Urethane C=0 stretching PUSLDH 3310 Urethane N-H stretching 1723 Urethane C=0 stretching

SLDH sample shows strong absorption bands in the range of 2850 - 2965 cm '1 corresponding to the -CH2- stretching vibration of the hydrocarbon tail present in each of the surfactant anions. The peak at 1560 cm'1 corresponds to carboxylic C = 0 groups present in stearate. The signal around 650 cm '1 originates from the lattice vibration of the hydroxide sheet and the broad­

band in the range 3 2 0 0 - 3 7 0 0 cm '1 come mainly from

Fig. 7. FTIR Spectra of PU and PUSLDH

Rys. 7. Widmo FTIR poliuretanu (PU) i poliuretanu za­

wierającego modyfikowany dwuwarstwowy hydroksy- związek

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20 m odyfikow ane H ydroksyzwiązki jako składnik n a n o k o m p o z y tó w

the O-H groups present in metal hydroxide layers and water molecules in interlayer space. The appearance of characteristic vibration bands for C 0 32 means that some C 0 32' still exits in the interlayer region.

FTIR spectra of pure PU and PU/SLDH nanocompo­

sites are shown in Figure 7. In case of these nanocompo­

sites apart peaks from LDHs, signals around 1722 and 3320 cm '1 descended from CO double bonds and N-H bonds of polyurethane are characteristic. This confirms the presence of SLDH in PU matrix.

3.5. Mechanical properties study

The effect of unmodified and modified LDH on the mechanical properties of PU/LDH nanocomposites have been studied and the results are summarized in Table 2.

Table 2. Mechanical properties of polyurethane and its nanocomposites

Tabela 2. Właściwości mechaniczne poliuretanu i jego kompozytów

Sample

Tensile Strength

(MPa)

Elonga­

tion at break (%)

100%

Modu­

lus (MPa)

300%

Modu­

lus (MPa)

Tear Strength

(N/mm)

PU 7.50 400 3.05 6.57 27.70

PULDH 9.05 485 3.86 7.61 32.50

PUSLDH 10.85 496 4.75 9.12 34.70

As reported in Table 2, incorporation of LDH im­

proves the mechanical properties of polyurethane elas­

tomer. The enhancement in tensile modulus may be ascribed to the resistance applied by LDH itself, as well as the orientation and high aspect ratio of the LDH plate­

lets. It is seen from Table 2 that the tensile strength (TS) and elongation at break (EB) for the nano composites containing unmodified and modified LDH are higher with respect to PU. TS is increased by 20% and 45% for PULDH and PUSLDH respectively. EB is increased by 21% and 24% for PU nanocomposites containing LDH and SLDH respectively. The increase in TS is caused by strong interfacial interaction between the hydroxyl groups of LDH and the polar urethane (-NHCOO) groups of PU through the hydrogen bonding, which is also confirmed by FTIR It also appears that the partially exfoliated LDH layers transfer stress from LDH itself and directly enhance the stiffness of PU nanocompo­

sites. The enhancement in EB may be caused by the entanglement of the polymer chain and the synergistic effect of chain slippage and orientation of LDH layers.

3.6. FESEM Analysis of LDH

Mg-Al-LDH clays usually show plate-like morpho­

logy. The size distribution of the particles depends mostly on the synthesis conditions and varies from few hundred nanometers to few micrometers in lateral

A)

Fig. 8. FESEM images of LDH (A) and SLDH (B) Rys. 8. Obrazy FESEM zarejestrowane dla czystego dwuwarstwowego hydroksyzwiązku (LDH) - (A) i mody­

fikowanego LDH (SLDH) - (B)

dimensions. In Figure 8 (A), the FESEM micrograph of the unm odified LDH shows this particle geometry, where the primary plate-like particles are characterized by distinct hexagonal shapes and sharp edges. The highly an isometric nature of these primary particles is also apparent. The lateral dimension of these plate-like particles varies with in few micrometers, whereas the thickness hardly exceeds few hundred nanometers. The regeneration process restores the metal hydroxide sheets of the LDH crystal. SLDH morphology is diffe­

rent, Figure 8(B). Particles have are needle shaped and their surface texture is dissimilar to that of LDH.

3.7. SEM Study of fractured surfaces

Surface of the nanocomposites gives an idea about the mechanism of fracture and dispersion of fillers in the polymer matrix. Figure 9 displays SEM micrographs of the tensile fractured surfaces of pure PU and its nano-

(7)

m odyfikow ane bydroksyzw iązki jako składnik n a n o k o m p o z y tó w 2 1

Fig. 9. SEM images o f tensile fractured surfaces (A), PU/Unmodified LDH (PULDH), (B) and PUSLDH (C)

Rys. 9. Obrazy SEM powierzchni po rozciąganiu próbek PU (A), PU/niemodyfikowanego LDH (PULDH) - (B) i PUSLDH (C)

composites containing 3 wt % of LDHs. The LDH filled PU nanocomposites, both unmodified and modified, shows rough fractured morphology in comparison to the pure one. The increase in roughness of the fractured sur­

face may be due to the dispersion of LDH in the PU matrix. Among the LDH filled PU nanocomposites, PUSLDH shows a highly rough and tortuous path of fracture compared to PU nanocomposites containing unmodified LDHs and pure PU. The dispersion of LDHs platelets in the rubber alters the crack path along the

direction depending on their orientation in the PU ma­

trix. Hence, it may form higher resistance to crack pro­

pagation that can lead to increase in tensile strength of the nanocomposites compared to the pure one.

4. Conclusion

In the present study sodium stearate, was used to modify Mg-Al-LDH in order to enlarge the interlayer distances and to make it more organophilic. Then SLDH was dispersed in the PU matrix by solution mixing fol­

lowed by mechanical mixing. The effect of modification of LDH on the properties of PU/LDH nanocomposites was studied. The XRD analysis of the modified LDH in­

dicated that stearate moiety was introducet into the interlayer space, which is reflected with an increased interlayer spacing (0.76 nm to 2.75 nm).

Thermal stability of all the modified LDHs improved in comparison to pure LDH. FESEM study reveals that the modification of LDH led to demonstrate a com­

pletely different morphology i.e., the hexagonal platelet structure of pure LDH has been transformed into irregu­

lar shape upon modification. TGA study of the PU/LDHs nanocomposites reveals the improved thermal proper­

ties in comparison to base elastomer. HRTEM study shows that the LDHs layers of SLDH are randomly dis­

persed in the PU matrix compared to agglomerated structure of pure LDH. Modified LDHs based nano­

composite shows better mechanical properties com­

pared to unmodified LDH added nanocomposites due to the better dispersion of modified LDHs in the PU matrix.

References

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Instytut Inżynierii

Materiałów Polimerowych i Barwników

Oddział Zamiejscowy Elastomerów i Technologii Gumy 05-820 Piastów, ul. Harcerska 30

tel. (022) 723-60-25, fax: (022) 723-71-96 www.impib.pl

Akredytowane przez PCA

LABORATORIUM BADAWCZE „Labgum"

Laboratorium jest wyspecjalizowane w badaniach wyrobów gumowych, m.in. różnego rodzaju elementów, uszczelnień, granulatu gumowego oraz surowców i mieszanek przeznaczonych do ich produkcji.

Posiada nowoczesną aparaturę badawczą, ma wdrożony system jakości zgodny z wymaganiami PN-EN ISO/IEC 17025:2005 i akredytację od 1998 r.

Laboratorium posiada

Certyfikat Akredytacji PCA Nr AB 147

w zakresie badań fizyko-chemicznych i mechanicznych gumy i wyrobów gumowych

Certyfikat KIWA - N.V. Certification and Inspection 0902111520JSHKIWA

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Z-ca Kierownika Laboratorium i Kierownik Zespołu Badania Właściwości Chemicznych:

dr inż. Małgorzata Piaskiewicz, tel. wew. 161, m.piaskiewicz@ipgum.pl, m.piaskiewicz@impib.pl Kierownik Zespołu Badania Właściwości Fizycznych:

mgr inż. Michał Lewandowski: tel. wew. 182, m.lewandowski@ipgum.pl, m.lewandowski@impib.pl

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