research article effect of different nucleating agents...

Research ArticleEffect of Different Nucleating Agents on the Crystallization ofZiegler-Natta Isotactic Polypropylene

Felipe Avalos-Belmontes1 Luis Francisco Ramos-deValle2

Adriana Berenice Espinoza-Martiacutenez2 Juan Guillermo Martiacutenez-Colunga2

Eduardo Ramiacuterez-Vargas2 Saul Saacutenchez-Valdeacutes2 Jose Carlos Ortiacutez-Cisneros1

Esperanza Elizabeth Martiacutenez-Segovia2 and Flora Itzel Beltraacuten-Ramiacuterez2

1Facultad de Ciencias Quımicas Universidad Autonoma de Coahuila (UAdeC) Boulevard V Carranza and Gonzalez-Lobo25000 Saltillo COAH Mexico2Centro de Investigacion en Quımica Aplicada (CIQA) Boulevard Enrique Reyna No 140 25294 Saltillo COAH Mexico

Correspondence should be addressed to Felipe Avalos-Belmontes favalosuadecedumxand Luis Francisco Ramos-deValle luisramosciqaedumx

Received 26 January 2016 Revised 6 May 2016 Accepted 17 May 2016

Academic Editor Marta Fernandez-Garcıa

Copyright copy 2016 Felipe Avalos-Belmontes et alThis is an open access article distributed under theCreativeCommonsAttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

Ziegler-Natta isotactic polypropylene (iPP) wasmelt mixed with four different nucleating agents (carbon nanotubes (CNT) carbonnanofibers (CNF) lithium benzoate (LiBe) and a sorbitol derivative (Millad)) in order to study their effect on the crystallization ofiPP It was found that the four different nucleating agents promote the alpha crystalline form At 001 wt the carbon nanoparticlesproduced the higher crystallization temperature ldquo119879

119888rdquo (sim119∘C) whereas at 010 wt LiBe and Millad produced a markedly higher

119879119888(sim125∘C) 119879

119888of pure iPP was 111∘C With 01 wt nucleating agent at 120∘C the crystallization half-life time of PP when using

LiBe or Millad was 15 times faster than for pure PP whereas when using carbon nanoparticles it was 20ndash25 times faster At 135∘Cwith 001 wt nucleating agent the isothermal crystallization process of iPP was completed after 25min as well as with MilladWith LiBe it was completed after just 15min and with any of the carbon nanoparticles it was practically over after only a coupleof minutes

1 Introduction

Isotactic polypropylene is an important polyolefin used in theglobalmarket due to the combination of very good propertiesand low cost However because of polypropylene being asemicrystalline polymer many of its properties depend on itscrystalline characteristics which can bemodified bymeans ofdifferent methods and techniquesThe addition of nucleatingagents for example will induce a more uniform crystal sizeand crystal structure This in turn will induce a highercrystallization temperature which eventually will result inshorter molding cycles Improvements in the mechanicaland thermal properties include increased modulus withoutsacrificing impact strength increased thermal stability [12] and increased clarity for special visual effects whenconcerning the optical properties [3]

Polypropylene with its relatively slow crystallization rateand crystal size from 50 to 150 120583m and depending on the par-ticular characteristics of the polymer and thermal treatmenthas a typical white appearance But by decreasing the crystalsize below the wavelength of visible light polypropylenebecomes quite transparent [1 4 5] When the nucleatingagent reduces the crystal size of the polypropylene to suchan extent the agent is also known as a clarifier Clarifiedpolypropylene presents higher clarity and improved polymerstrength This makes the polymer a promising substituteof polystyrene in some applications Currently clarifiedpolypropylene finds application in housewares containersblow molded bottles medical syringes and vials thermo-formed containers and extruded and blown films [6]

In addition to the above-mentioned effects the contentof alpha beta and gamma crystalline forms can also be

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2016 Article ID 9839201 9 pageshttpdxdoiorg10115520169839201

2 International Journal of Polymer Science

Table 1 Comparison of size and surface area of the four different nucleating agents

CNT CNF LiBe Millad119871 (120583m) 10 20 mdash mdash119863 (120583m) 0050 0120 100 150120588 (120583g120583m3) 21 times 106 21 times 106 11 times 106 11 times 106

ApproximatelyVol of 1 particle (120583m3) 002 023 524 1767Wt of 1 particle (120583g) 412minus8 4750minus8 576minus4 1940minus4

Number of particles in 100mg 243+12 2110+12 174+8 051+8

Surface area of 1 particle (120583m2) 160 75 314 707Surface area in 100mg (120583m2) 381+12 159+12 545+10 364+10

Ratio of surface areaslowast 100 40 15 1lowastRatio of surface areas of the different nucleating agents to Millad when having 100mg of each taking the surface area of 100 mg of Millad as 1 For example100mg of CNT will have 100 times the surface area of 100mg of MilladCNT and CNF were considered as cylinders and LiBe and Millad as spheres for the calculation of volume weight and surface areamdash at any wt there will always be between 30 and 100 times more surface area in carbon nanoparticles than in LiBe or Millad

altered by selecting the appropriate nucleating agent [7 8]In the last 10 years carbon nanostructures such as carbonnanotubes (CNT) and carbon nanofibers (CNF) have beenused as effective nucleating agents for polypropylene [9 10]Some authors have reported that the addition of nanotubesfrom 01 to 5wt increased the crystallization temperatureof PP composites with respect to the pure PP and enhancedthe mechanical electrical and thermal properties [11 12]

This paper examines the nucleating ability of very smallamounts of CNT CNF dimethylbenzylidene sorbitol (Mil-lad) and lithium benzoate (LiBe) for the crystallization of anisotactic Ziegler-Natta polypropylene

2 Experimental

21 Materials The isotactic polypropylene (iPP) used inthis study was a Ziegler-Natta polypropylene from IndelproMexico with an average molecular weight (MW) of 300000molecular weight distribution (MWD) of 34 and melt flowindex (MFI) (at 230∘C with 216 kg) of 11 g10min ThisiPP presented a crystallization temperature (119879

119888) and melting

temperature (119879119898) of 111 and 160∘C respectively

Chemicals used as nucleating agents were multiwalledcarbon nanotubes (CNT) from NanoLab USA carbonnanofibers (CNF) Pyrograf III from Applied SciencesUSA lithium benzoate (LiBe) with a melting point ofsim370∘C fromMicronisers Ltd Australia and 1324-bis(34-dimethylbenzylidene sorbitol) Millad 3988 (Millad) with amelting point of sim250∘C fromMilliken USA

ConsideringCNTandCNFwith a rod-like form andLiBeand Millad with a quasi-spherical form Table 1 presents acomparison of their approximate size and geometric charac-teristics

22 Preparation of Composites iPP composites with 01 wtof each nucleating agent were prepared in a 250 cm3 capacitymixing chamber with roller type rotors coupled to a Braben-der torque rheometerThe composites were prepared viamelt

mixing for a period of 12min at 170∘C and 50 rpm rotorspeed

These composites with 01 wt of nucleating agent werethen used as master batches and diluted for the preparationof the 0001 001 005 and 008wt of nucleating agent

23 Characterization

231 Differential Scanning Calorimetry (DSC) DSC mea-surements were performed on a Perkin Elmer DSC 7 Pyrisunder a nitrogen flow Weight of each sample was always10 plusmn 1mg

The effect of the different nucleating agents on the rateof crystallization and on the nucleating efficiency of the dif-ferent nucleating agents was studied via dynamic conditionswhereas the effect of the different nucleating agents on thekinetic characteristics of the process of crystallization wasstudied via isothermal conditions

232 Dynamic Crystallization The crystallization tempera-ture (119879

119888) was calculated as follow samples were first heated

from room temperature to 200∘C at 10∘Cmin and held therefor 3min to erase any thermal history The samples werethen cooled down to 50∘C at minus10∘Cmin From this coolingprocess the temperature at the maximum peak was taken as119879119888

233 Isothermal Crystallization These were carried out atvarious isothermal temperatures ranging from 115 to 127∘CAll samples were first heated to 200∘C at 10∘Cmin andheld there for 3min to erase the previous thermal historySubsequently they were cooled at minus50∘Cmin to the desiredisothermal temperature and held at that temperature untilcomplete crystallization

234 PolarizingOpticalMicroscopy (POM) Crystallinemor-phology of iPP and its composites was investigated througha Mettler Toledo FP900 coupled to a Zeiss contrast phasemicroscope Additionally a Samsung video camera modelSCC-131A was attached to the microscope The amplification

International Journal of Polymer Science 3

Inte

nsity

5 10 15 20 25 30 35

CNTZN-iPP

2120579

(110) 120572(040) 120572

(130) 120572

Xc = 4347

(a)

Inte

nsity

5 10 15 20 25 30 35

CNFZN-iPP

2120579

Xc = 4351

(b)

Inte

nsity

5 10 15 20 25 30 35

LiBeZN-iPP

2120579

Xc = 4347

(c)

Inte

nsity

Millad

5 10 15 20 25 30 352120579

ZN-iPP

Xc = 4860

(d)

Figure 1 WAXD diffractograms of iPP composites at 01 wt of nucleating agent

used was 10x times 20x The experiments were performedusing isothermal crystallization Samples were heated to200∘C at a heating rate of 10∘Cmin and held there for 3minutes to remove thermal history and then cooled downto 135∘C at minus20∘Cmin The samples were then held at 135∘Cfor 30min All experiments were run in air atmosphere Thetime at which each sample reached 119879

119888 was designated as

time zero (1199050) In each case a photograph was taken at time

zero thereafter a new photograph was taken either every30 sec 15 sec or more often depending on how fast thecrystallization occurred

235Wide Angle X-Ray Diffraction (WAXD) The crystallinestructure of all samples was assessed using X-ray diffractionanalysis In this case the composites with 01 wt of additivewere selected to determine the crystal type induced by theaddition of the different nucleating agentsThe XRD analyseswere carried out in a Siemens D5000 diffractometer from 5

to 35 in 2120579 Disc shaped samples of 25mm in diameter and1mm thick were analyzed

3 Results and Discussion

31 Crystalline Structure of iPP Composites To study theeffect of the different nucleating agents on the polymorphismof iPP all samples were examined by means of WAXD It wasreasoned that if therewas any formation of beta crystals by theincorporation of the nucleating agents this phenomenonwillbe more evident at the highest concentrationThus the X-rayanalysis was carried out on the composites with 01 wt ofnucleating agent Figure 1 shows the WAXD patterns of pureiPP and iPPwith nucleating agents It can be observed that thefour composites display the same characteristic diffractingpeaks corresponding to the planes (110) (040) and (130) ofthe 120572-form whereas the peak corresponding to the plane(300) characteristic of the 120573 form (at around the 160∘ on the


110

112

114

116

118

120

122

124

126

Concentration (wt)

MilladLiBe

CNFCNT

000 002 004 006 008 010

Crys

talli

zatio

n te

mpTc

(∘C)

Figure 2 Variation of the crystallization temperature (119879119888) of iPP

with the nucleating agents concentration (0001 001 005 and010 wt)

2120579 range) is absentThis confirms thatMillad LiBe CNF andCNT are 120572-nucleating agents for iPP

In this respect it has been reported that Millad and CNTare not able to induce the 120573 form [13ndash15] while there is noreported data for the CNF and LiBe Furthermore it can beobserved in Figure 1 that there was an increase of the (040)plane at the expense of the (110) plane The LiBe nucleatingagent induces the greatest displacement to the alpha formwhile Millad exerts an effect comparable to that of the carbonnanoparticles

In this respect the crystallinity degree (119883119888) of the com-

posites was also determined from the X-ray diffractogramsThis crystalline content was obtained from the total areaunder the diffractograms after subtracting the area corre-sponding to the amorphous phase [16]

The 119883119888 values are included inside the WAXD plots

of Figure 1 Note that these crystalline degrees (119883119888) were

obtained on samples with 01 wt of nucleating agent For thepure polymer the crystalline content was found to be 420and in general terms it can be said that the incorporationof the studied nucleating agents slightly increased the 119883

119888

of the carbon nanoparticles composites (by sim15 percentagepoint ie 420 to 435) whereas it markedly increased the119883119888 of the LiBe and Millad composites (by sim70 percentage

points ie 420 to 490)

32 Nonisothermal Crystallization Behavior of iPP Compos-ites Table 2 presents the particular crystallization temper-atures of the iPP composites with the different nucleatingagents

Additionally Figure 2 presents the effect of the differentnucleating agents on 119879

119888 as a function of concentration

in nonisothermal experiments CNT and CNF showed astrong nucleating effect at very low concentrations (0001

Table 2 Crystallization temperature (∘C) of the iPP composites asa function of the nucleating agent concentration

Nucleating agentconcentration wt Millad LiBe CNF CNT

0001 111 111 117 1166001 110 116 119 1185005 111 123 1195 120010 124 125 120 1205

and 001 wt) increasing the crystallization temperature upto 119-120∘C but this effect leveled off that is the carbonnanoparticles reached their saturation point and119879

119888remained

at ca 120∘C even at the highest concentration (010 wt)LiBe on the other hand started to have an effect on the

crystallization temperature at a slightly higher concentrationand thereafter even surpassed the effect of the carbonnanoparticles reaching a crystallization temperature above124∘C at 010 wt [17] Finally Millad showed no effect atthe low concentrations but showed an excellent effect onincreasing119879

119888at the highest concentration (010wt) equaling

the effect of LiBePolypropylene is known to present polymorphism which

depends on the catalysts and polymerization conditions usedduring its synthesis Its chain structure can contain randomlydistributed stereo andor regio defects In this sence van derMeer et al [18] found that the crystal growth rate decreaseslinearly with the fraction of defects but it is more affected bythe presence of regio defects than stereo defects

While studying the crystallinity and mechanical prop-erties of metallocene catalyzed polypropylene De Rosa etal [19] found that the presence of rr defects affects itspolymorphism and mechanical properties inducing the for-mation of gamma type crystals The authors found thatwhen the concentration of rr defects is low (3-4) thepolymer presents a melting temperature above 130∘C andmechanically the polymer behaves as a stiff thermoplasticmaterial But if the concentration of rr defects is greater (4ndash6) the melting temperature lies between 115 and 120∘C andthe polymer behaves as a flexible thermoplastic material

On the other hand Krache et al [7] studied the effect ofnucleating agents on the polymorphism of metallocene andZiegler-Natta polypropylenes and found that the formationof beta type crystals depends on the type and concentrationof nucleating agent as well as on the cooling rate As aresult the decreased tacticity of metallocene polypropylenein combination with the effect of nucleating agents rendersa more complex morphology than that in the Ziegler-Nattapolypropylene In the metallocene samples the stereo defectsare randomly distributed and therefore are more likely to beincorporated within crystals

This explains why 119879119888of Ziegler-Natta iPP composites

is higher than that of metallocene iPP composites reportedelsewhere [5] On the other hand Beck [20] found thatthe type of structure of the nucleating agent determines itseffectiveness In this sense it is known that some nucleatingagents of PP act via epitaxial interactions such as benzoic


Table 3 Nucleating efficiency [] of the four different nucleatingagents on iPP composites as a function of concentration


0001 1 1 246 209001 2 15 307 283005 10 40 326 338008 26 49 346 351010 45 52 357 363

acid and its salts [21] The more ordered structure of Ziegler-Natta iPP as compared to that of metallocene iPP favorsthe crystallographic interactions with nucleating agents asobserved in the 119879

119888results presented herewith particularly

with those agents that have similar unit cell structure to thatof PP as LiBe [22] The carbon nanoparticles due to theirvery high surface area reach the saturation point very rapidlythe great number of nuclei sites overcomes the differencein the crystallizable block segments of the polymer Thiswould explain why at very low concentrations the carbonnanoparticles perform better in Ziegler-Natta iPP than inmetallocene iPP In this case due to the small numberof nuclei particles the effect of the crystallizable polymersegments length is dominant

33 Nucleating Efficiency in terms of 119879119888 There are two

ways of assessing the nucleating efficiency of additives forpolypropylene depending on the way the crystallizationtakes place One is when the crystallization is carried outunder dynamic conditions where the measured parameteris the crystallization temperature and the simplest way isto establish an arbitrary scale [20] or use Fillonrsquos method[23]This method defines the ideal situation of self-nucleatedpolypropylene and takes the crystallization temperature ofthe self-nucleated PP (119879

1198882max

) as the upper limit (100) whichin this case was taken as 138∘C [13 24 25] However thecrystallization temperature of the pure polymer (119879

1198881

) is thelower limit (0) and in this case it was taken as 110∘C Thusthe nucleating efficiency is given by

NE = 100 lowast119879119888NAminus 1198791198881

1198791198882maxminus 1198791198881

(1)

where 119879119888NA

is the measured crystallization temperature with aparticular nucleating agent

Self-nucleation studies for polypropylene [13 24 25] givevalues for 119879

1198882max

(the upper limit) between 137 and 140∘C fora Ziegler-Natta iPP that is approximately 25 to 28 degreesabove the crystallization temperature of the pure polymer Inthe present study119879

1198882max

of iPPwas taken as 138∘CThis value isan average of 28 degrees above the crystallization temperatureof the pure polymer (119879

1198881

= 110∘C)Following (1) the efficiency of the nucleating agents is

presented in Table 3

0

10

20

30

40

50

60

Nuc

leat

ing

effici

ency

()

Concentration (wt)000 002 004 006 008 010

MilladLiBe

CNFCNT

Figure 3 Variation of the nucleating efficiency of the differentnucleating agents with their concentration (0001 001 005 and010 wt)

The resulting nucleating efficiencies are not especiallyhigh Higher results have been reported [25ndash27] but whathas to be kept in mind is that the highest nucleating agentconcentration used was 01 wt which is lower than thatreported in many similar studies especially for Millad andLiBe [28 29]

However it is worth to emphasize the good nucleatingefficiency of Millad and LiBe when used at a concentrationof 01 wt as shown in Table 3 and Figure 3

What is clear from Figure 3 is that the carbon nanopar-ticles apparently tend to reach their saturation point at verylow concentrations 001ndash005wt where their NE reachesa maximum of ca 30ndash35 Millad and LiBe on the otherhand seem to be very poor nucleating agents at the lowconcentrations studied but easily surpass the NE of thecarbon nanoparticles at concentrations above 010 wt At010 wt Millad and LiBe do not even seem to be near theirsaturation point

The above mentioned could be because at any weightconcentration the number of carbon nanoparticles surpassesthe number of Millad or LiBe particles by approximately 6orders of magnitude (Table 1) That is at the low concentra-tions used in this study the number of Millad or LiBe nucleiis still very small compared to the number of CNT or CNFnuclei And it is until the Millad or LiBe nuclei populationincreases when these start to show the strong nucleatingeffect The small number of Millad or LiBe particles at thelower concentrations gives rise to the large spherulite sizesobserved in Figure 5

The crystallization kinetics of the PP compositions stud-ied was carried out based on the Avrami model This theoryhas been often used to analyze the crystallization of PP [19ndash21] This model does not account for the secondary crystal-lization but it has been found that secondary crystallizationis not relevant in PP [8]


00

02

04

06

08

10

Relat

ive c

rysta

llini

ty (

)

Time (min)

PPCNTCNF

LiBeMillad

00 05 10 15 20 25 30 35 40

(a)

CNTCNFLiBe

MilladPP

2

2 3 4

1

1

0

0

minus1

minus1

minus2

minus2

minus3

minus3

minus4

minus5

minus6

ln (time)

ln(1

[minusln

minus120572

)](b)

Figure 4 (a) Variation of the relative crystallinity versus time of pure PP and PP with 01 wt nucleating agent (b) Avrami plots of pure PPand PP with 01 wt nucleating agent at 120∘C

To study the isothermal crystallization the followingequation derived from the Avrami model was used

120572 = 1 minus exp (minus119870119905119899)

1 minus 120572 = exp (minus119870119905119899)

ln (1 minus 120572) = minus119870119905119899 997888rarr

minus ln (1 minus 120572) = 119870119905119899

ln [minus ln (1 minus 120572)] = 119899 sdot ln (119870119905)

ln [minusln (1 minus 120572)] = 119899 sdot ln (119905) + 119899 sdot ln (119870)

(2)

where 120572 is the weight fraction that has passed from theamorphous to the crystalline state as a function of the time119905 119870 is the Avrami constant and 119899 is the Avrami exponent119870 and 119899 are used to interpret the nucleation mechanism andthe overall crystallization rate of the polymer 119870 and 119899 areobtained from a plot of ln[minus ln(1 minus 120572)] versus ln(119905) Figures4(a) and 4(b) show the Avrami plots for the PP compositionsstudied

Values of 119870 119899 and 11990512

are presented in Table 4 Thefractional 119899 values are accounted for in the Avrami theoryby assuming some overlapping of primary nucleation andgrowth [22] 119899 values obtained are between 20 and 30 forall the PP compositions studied

The effect of the nucleating agents is clearly seen inthe development of the crystallization rate (Table 4) Thecrystallization ratemdashmeasured by the half-life time of crys-tallization which was determined experimentallymdashfor thegiven temperature of 120∘C indicates an increase in thevelocity of crystallization induced by the nucleating agent

Table 4 Crystallization temperature 119879119888 Avramirsquos constant 119870

Avramirsquos exponent 119899 and crystallization half-life time 11990512

forPP at different temperatures In all cases the nucleating agentconcentration was 01 wt

Sample 119879119888[∘C] 119899 119870 119905

12[min]

PP

1150 258 017 171170 271 0052 321200 261 0002 821220 249 00018 105

PP-CNT

1150 284 7411 0171200 274 3719 0321250 248 6002 0591270 258 0606 082

PP-CNF

1150 310 13432 0181200 298 480 0411250 252 37 0871270 265 179 139

PP-LiBe

1200 276 1382 0521220 267 474 0811250 274 067 1491270 258 008 234

PP-Millad

1180 347 1945 0401200 250 914 0521250 193 115 2521270 205 005 480

(Table 4) With CNT and CNF it increases by a factor of 20ndash25 compared to the pure PP and with either LiBe or Milladit increases by a factor of 15


MilladBlank LiBe CNT CNF0min

5min

10min

15min

20min

25min

Figure 5 Crystallization process and crystal size of pure iPP and nucleated iPP composites at 135∘C with 001 wt of nucleating agent

The spherulitic growth rate and number of nuclei arereflected in the Avrami constant 119870 In this case the higher119870 values indicate a higher number of nuclei for the PPcompositions with carbon nanoparticles [2]

34 Spherulite Growth of iPP in Composites during Isother-mal Crystallization After assessing the different nucleatingagents by their influence on the crystallization temperaturenucleating efficiency and crystallization half-life time their


effect on the crystal size and crystallization rate of iPP is nowexamined In this case the nucleating agent concentrationwas 001 wt

Results show that in the case of the PP composites themain difference in nucleating activity is as follows (1) At010 wt the nucleating effect of Millad and LiBe is superiorto that of both CNF and CNT (2) But at 001 wt thenucleating effect of carbon nanoparticles is superior to thatof Millad or LiBe

The analysis of spherulitic growth under optical micros-copy was carried out at 135∘C This temperature was chosensimply because at lower temperatures the observed changesoccurred very rapid

Figure 5 shows the photographs of pure polypropyleneand composites during isothermal crystallization at 135∘C

It can be observed in Figure 5 that after 5min thecrystal concentration in the carbon nanoparticles compositesappears higher than for the LiBe composite For the Milladcomposite on the other hand there is no nucleating effect atall and the crystal size remains approximately the same as thatof the pure polymer

Looking at the photographs it can be assumed that thecrystallization process of the pure polymer is completed after25min and the same can be said of the Millad composite

The crystallization process of the LiBe composite on theother hand is completed around 10ndash15 minutes Thereafterthe two remaining photographs at 20 and 25min look verysimilar

On the contrary the crystallization process for the carbonnanoparticles composites is practically over after only acouple of minutes The process is so fast that five minutesappear too long to differentiate the process

But considering the effects of the studied nucleatingagents on the crystallization temperature the nucleatingefficiency and the crystallization half-life time it can clearlybe assumed that at this low concentration of 001 wtthe carbon nanoparticles are right at their saturation pointwhereas LiBe and Millad are far below this point

It has been reported [30] that PPCNT nanocompositeswith CNT contents above those studied here (025 and05 wt) have higher nucleation density (number of nucleiin the polymer mass that give rise to crystals) than the purePP and that not every nanotube can act as a nucleating siteduring crystallization The authors commented that it seemsthat a minimum size of nanotube stack is needed to providenuclei for crystal formation In our case nanocompositescontaining lower CNT and CNF contents (001 wt) showedsimilar nucleation densities It appears then that as shownin our crystallization temperature nucleating efficiency andcrystallization half-life time results the carbon nanoparticlesreach their saturation point at very low concentration

4 Conclusions

The effect of different nucleating agents (carbon nanotubescarbon nanofibers lithium benzoate and a sorbitol deriva-tive) on the crystallization of Ziegler-Natta iPP was studied

It was found that the four different nucleating agentspromote the alpha crystalline form

At the lower concentrations studied (0001ndash001 wt) thecarbon nanoparticles produced the higher 119879

119888 whereas at the

highest concentration (01 wt) lithium benzoate and thesorbitol derivative produced a markedly higher 119879

119888

With 01 wt nucleating agent at 120∘C the crystalliza-tion half-life time of PP when using LiBe or Millad was 15times faster than for pure PP whereas when using carbonnanoparticles it was 20ndash25 times faster

At 135∘C with 001 wt of nucleating agent the crystal-lization process of the Millad composite as well as the purepolymer is completed after 25min But the crystallizationprocess of the LiBe composite is completed after only 15minand that of the carbon nanoparticles composites is practicallyover after only a couple of minutes

The carbon nanoparticles reach their saturation pointat very low concentration namely 001ndash005wt whereasthe LiBe and Millad did not even appear to have reachedtheir saturation point at the highest concentration studied(01 wt)

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

Two of the authors (Esperanza Elizabeth Martınez-Segoviaand Flora Itzel Beltran-Ramırez) thankCONACYT for grant-ing them scholarships to carry their PhD studies Alsothe authors gratefully acknowledge the financial supportof CONACYT through Projects nos CB-222805 and LN-232753 Finally the authors wish to thankM SanchezAdameFrancisco Zendejo Rodrigo Cedillo Conc Gonzalez JesusRodrıguez Luis E Reyes Alejandro Espinoza E Hurtado-Suarez and D Alvarado for their technical and informaticssupport

References

[1] J H Botkin N Dunski andDMaeder ImprovingMolding Pro-ductivity and EnhancingMEchanical Properties of Polypropylenewith Nucleating Agents Ciba Speciality Chemicals 2002

[2] K Mai K Wang Z Han and H Zeng ldquoStudy on the thermalstability of heterogeneous nucleation effect of polypropylenenucleated by different nucleating agentsrdquo Journal of AppliedPolymer Science vol 83 no 8 pp 1643ndash1650 2002

[3] A Menyhard M Gahleitner J Varga et al ldquoThe influenceof nucleus density on optical properties in nucleated isotacticpolypropylenerdquo European Polymer Journal vol 45 no 11 pp3138ndash3148 2009

[4] S Nagasawa A Fujimori T Masuko andM Iguchi ldquoCrystalli-sation of polypropylene containing nucleatorsrdquoPolymer vol 46no 14 pp 5241ndash5250 2005

[5] M Schmidt J J Wittmann R Kress et al ldquoCrystal structure ofa highly efficient clarifying agent for isotactic polypropylenerdquoCrystal Growth and Design vol 12 no 5 pp 2543ndash2551 2012

[6] D Vanzin and J Cooke ldquoA novel clarifyingnucleating agentsystem for polyolefinsrdquo in Proceedings of the Annual Technical


Conference of the Society of Plastics Engineers (ANTEC rsquo91) vol49 pp 1934ndash1941 Montreal Canada May 1991

[7] R Krache R Benavente J M Lopez-Majada J M PerenaM L Cerrada and E Perez ldquoCompetition between 120572 120573and 120574 polymorphs in a 120573-nucleated metallocenic isotacticpolypropylenerdquo Macromolecules vol 40 no 19 pp 6871ndash68782007

[8] C Mathieu AThierry J CWittmann and B Lotz ldquoSpecificityand versatility of nucleating agents toward isotactic polypropy-lene crystal phasesrdquo Journal of Polymer Science Part B PolymerPhysics vol 40 no 22 pp 2504ndash2515 2002

[9] K Song Y Zhang JMeng et al ldquoStructural polymer-based car-bon nanotube composite fibers understanding the processing-structure-performance relationshiprdquoMaterials vol 6 no 6 pp2543ndash2577 2013

[10] D Xu and Z Wang ldquoRole of multi-wall carbon nanotube net-work in composites to crystallization of isotactic polypropylenematrixrdquo Polymer vol 49 no 1 pp 330ndash338 2008

[11] C Min X Shen Z Shi L Chen and Z Xu ldquoThe electri-cal properties and conducting mechanisms of carbon nan-otubepolymer nanocomposites a reviewrdquo PolymermdashPlasticsTechnology and Engineering vol 49 no 12 pp 1172ndash1181 2010

[12] S P Bao and S C Tjong ldquoMechanical behaviors of polypropy-lenecarbon nanotube nanocomposites the effects of loadingrate and temperaturerdquoMaterials Science and Engineering A vol485 no 1-2 pp 508ndash516 2008

[13] C Marco G Ellis M A Gomez and J M Arribas ldquoCompara-tive study of the nucleation activity of third-generation sorbitol-based nucleating agents for isotactic polypropylenerdquo Journal ofApplied Polymer Science vol 84 no 13 pp 2440ndash2450 2002

[14] Y Mubarak P J Martin and E Harkin-Jones ldquoEffect ofnucleating agents and pigments on crystallisation morphologyand mechanical properties of polypropylenerdquo Plastics Rubberand Composites Processing and Applications vol 29 no 7 pp307ndash315 2000

[15] M-K Seo J-R Lee and S-J Park ldquoCrystallization kinetics andinterfacial behaviors of polypropylene composites reinforcedwith multi-walled carbon nanotubesrdquo Materials Science andEngineering A vol 404 no 1-2 pp 79ndash84 2005

[16] N S Murthy and H Minor ldquoGeneral procedure for evaluatingamorphous scattering and crystallinity from X-ray diffractionscans of semicrystalline polymersrdquo Polymer vol 31 no 6 pp996ndash1002 1990

[17] S Reyes-de Vaaben A Aguilar F Avalos and L F Ramos-deValle ldquoCarbon nanoparticles as effective nucleating agents forpolypropylenerdquo Journal of Thermal Analysis and Calorimetryvol 93 no 3 pp 947ndash952 2008

[18] D W van der Meer J Varga and G J Vancso ldquoThe influenceof chain defects on the crystallisation behaviour of isotacticpolypropylenerdquo eXPRESS Polymer Letters vol 9 no 3 pp 233ndash254 2015

[19] C De Rosa F Auriemma A Di Capua et al ldquoStructure-property correlations in polypropylene from metallocene cat-alysts stereodefective regioregular isotactic polypropylenerdquoJournal of the American Chemical Society vol 126 no 51 pp17040ndash17049 2004

[20] H N Beck ldquoHeterogeneous nucleating agents for polypropy-lene crystallizationrdquo Journal of Applied Polymer Science vol 11no 5 pp 673ndash685 1967

[21] W Stocker S N Magonov H-J Cantow J C Wittmann andB Lotz ldquoContact faces of epitaxially crystallized 120572- and 120574-phase

isotactic polypropylene observed by atomic force microscopyrdquoMacromolecules vol 26 no 22 pp 5915ndash5923 1993

[22] M M Stasova ldquoStructure of the tetragonal modification ofammonium nitraterdquo Kristallografya (Crystallography Reports)vol 4 pp 242ndash243 1959

[23] B Fillon A Thierry B Lotz and J C Wittmann ldquoEfficiencyscale for polymer nucleating agentsrdquo Journal of Thermal Analy-sis vol 42 no 4 pp 721ndash731 1994

[24] J Varga I Mudra and G W Ehrenstein ldquoCrystallizationand melting of 120573-nucleated isotactic polypropylenerdquo Journal ofThermal Analysis and Calorimetry vol 56 no 3 pp 1047ndash10571999

[25] J Kang H Peng B Wang et al ldquoInvestigation on the self-nucleation behavior of controlled-rheology polypropylenerdquoJournal of Macromolecular Science Part B Physics vol 54 no2 pp 127ndash142 2015

[26] M Naffakh Z Martın N Fanegas C Marco M A Gomezand I Jimenez ldquoInfluence of inorganic fullerene-like WS2nanoparticles on the thermal behavior of isotactic polypropy-lenerdquo Journal of Polymer Science Part B Polymer Physics vol45 no 16 pp 2309ndash2321 2007

[27] A Menyhard and J Varga ldquoThe effect of compatibilizers onthe crystallisation melting and polymorphic composition of120573-nucleated isotactic polypropylene and polyamide 6 blendsrdquoEuropean Polymer Journal vol 42 no 12 pp 3257ndash3268 2006

[28] Y-F Zhang ldquoComparison of nucleation effects of organic phos-phorous and sorbitol derivative nucleating agents in isotacticpolypropylenerdquo Journal of Macromolecular Science Part BPhysics vol 47 no 6 pp 1188ndash1196 2008

[29] Y Jin A Hiltner and E Baer ldquoEffect of a sorbitol nucleatingagent on fractionated crystallization of polypropylene dropletsrdquoJournal of Polymer Science Part B Polymer Physics vol 45 no14 pp 1788ndash1797 2007

[30] M Razavi-Nouri M Ghorbanzadeh-Ahangari A Fereidoonand M Jahanshahi ldquoEffect of carbon nanotubes content oncrystallization kinetics and morphology of polypropylenerdquoPolymer Testing vol 28 no 1 pp 46ndash52 2009

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Table 1 Comparison of size and surface area of the four different nucleating agents

CNT CNF LiBe Millad119871 (120583m) 10 20 mdash mdash119863 (120583m) 0050 0120 100 150120588 (120583g120583m3) 21 times 106 21 times 106 11 times 106 11 times 106

ApproximatelyVol of 1 particle (120583m3) 002 023 524 1767Wt of 1 particle (120583g) 412minus8 4750minus8 576minus4 1940minus4

Number of particles in 100mg 243+12 2110+12 174+8 051+8

Surface area of 1 particle (120583m2) 160 75 314 707Surface area in 100mg (120583m2) 381+12 159+12 545+10 364+10

Ratio of surface areaslowast 100 40 15 1lowastRatio of surface areas of the different nucleating agents to Millad when having 100mg of each taking the surface area of 100 mg of Millad as 1 For example100mg of CNT will have 100 times the surface area of 100mg of MilladCNT and CNF were considered as cylinders and LiBe and Millad as spheres for the calculation of volume weight and surface areamdash at any wt there will always be between 30 and 100 times more surface area in carbon nanoparticles than in LiBe or Millad

altered by selecting the appropriate nucleating agent [7 8]In the last 10 years carbon nanostructures such as carbonnanotubes (CNT) and carbon nanofibers (CNF) have beenused as effective nucleating agents for polypropylene [9 10]Some authors have reported that the addition of nanotubesfrom 01 to 5wt increased the crystallization temperatureof PP composites with respect to the pure PP and enhancedthe mechanical electrical and thermal properties [11 12]

This paper examines the nucleating ability of very smallamounts of CNT CNF dimethylbenzylidene sorbitol (Mil-lad) and lithium benzoate (LiBe) for the crystallization of anisotactic Ziegler-Natta polypropylene

2 Experimental

21 Materials The isotactic polypropylene (iPP) used inthis study was a Ziegler-Natta polypropylene from IndelproMexico with an average molecular weight (MW) of 300000molecular weight distribution (MWD) of 34 and melt flowindex (MFI) (at 230∘C with 216 kg) of 11 g10min ThisiPP presented a crystallization temperature (119879

119888) and melting

temperature (119879119898) of 111 and 160∘C respectively

Chemicals used as nucleating agents were multiwalledcarbon nanotubes (CNT) from NanoLab USA carbonnanofibers (CNF) Pyrograf III from Applied SciencesUSA lithium benzoate (LiBe) with a melting point ofsim370∘C fromMicronisers Ltd Australia and 1324-bis(34-dimethylbenzylidene sorbitol) Millad 3988 (Millad) with amelting point of sim250∘C fromMilliken USA

ConsideringCNTandCNFwith a rod-like form andLiBeand Millad with a quasi-spherical form Table 1 presents acomparison of their approximate size and geometric charac-teristics

22 Preparation of Composites iPP composites with 01 wtof each nucleating agent were prepared in a 250 cm3 capacitymixing chamber with roller type rotors coupled to a Braben-der torque rheometerThe composites were prepared viamelt

mixing for a period of 12min at 170∘C and 50 rpm rotorspeed

These composites with 01 wt of nucleating agent werethen used as master batches and diluted for the preparationof the 0001 001 005 and 008wt of nucleating agent

23 Characterization

231 Differential Scanning Calorimetry (DSC) DSC mea-surements were performed on a Perkin Elmer DSC 7 Pyrisunder a nitrogen flow Weight of each sample was always10 plusmn 1mg

The effect of the different nucleating agents on the rateof crystallization and on the nucleating efficiency of the dif-ferent nucleating agents was studied via dynamic conditionswhereas the effect of the different nucleating agents on thekinetic characteristics of the process of crystallization wasstudied via isothermal conditions

232 Dynamic Crystallization The crystallization tempera-ture (119879

119888) was calculated as follow samples were first heated

from room temperature to 200∘C at 10∘Cmin and held therefor 3min to erase any thermal history The samples werethen cooled down to 50∘C at minus10∘Cmin From this coolingprocess the temperature at the maximum peak was taken as119879119888

233 Isothermal Crystallization These were carried out atvarious isothermal temperatures ranging from 115 to 127∘CAll samples were first heated to 200∘C at 10∘Cmin andheld there for 3min to erase the previous thermal historySubsequently they were cooled at minus50∘Cmin to the desiredisothermal temperature and held at that temperature untilcomplete crystallization

234 PolarizingOpticalMicroscopy (POM) Crystallinemor-phology of iPP and its composites was investigated througha Mettler Toledo FP900 coupled to a Zeiss contrast phasemicroscope Additionally a Samsung video camera modelSCC-131A was attached to the microscope The amplification


Inte

nsity

5 10 15 20 25 30 35

CNTZN-iPP

2120579

(110) 120572(040) 120572

(130) 120572

Xc = 4347

(a)

Inte

nsity

5 10 15 20 25 30 35

CNFZN-iPP

2120579

Xc = 4351

(b)

Inte

nsity

5 10 15 20 25 30 35

LiBeZN-iPP

2120579

Xc = 4347

(c)

Inte

nsity

Millad

5 10 15 20 25 30 352120579

ZN-iPP

Xc = 4860

(d)











110

112

114

116

118

120

122

124

126

Concentration (wt)

MilladLiBe

CNFCNT

000 002 004 006 008 010

Crys

talli

zatio

n te

mpTc

(∘C)










119888









0001 111 111 117 1166001 110 116 119 1185005 111 123 1195 120010 124 125 120 1205


119888remained













0001 1 1 246 209001 2 15 307 283005 10 40 326 338008 26 49 346 351010 45 52 357 363






1198882max


1198881



1198791198882maxminus 1198791198881

(1)

where 119879119888NA



1198882max


1198882max


1198881



0

10

20

30

40

50

60

Nuc

leat

ing

effici

ency

()


MilladLiBe

CNFCNT








00

02

04

06

08

10

Relat

ive c

rysta

llini

ty (

)

Time (min)

PPCNTCNF

LiBeMillad

00 05 10 15 20 25 30 35 40

(a)

CNTCNFLiBe

MilladPP

2

2 3 4

1

1

0

0

minus1

minus1

minus2

minus2

minus3

minus3

minus4

minus5

minus6

ln (time)

ln(1

[minusln

minus120572

)](b)



120572 = 1 minus exp (minus119870119905119899)

1 minus 120572 = exp (minus119870119905119899)


minus ln (1 minus 120572) = 119870119905119899



(2)


Values of 119870 119899 and 11990512






Sample 119879119888[∘C] 119899 119870 119905

12[min]

PP

1150 258 017 171170 271 0052 321200 261 0002 821220 249 00018 105

PP-CNT

1150 284 7411 0171200 274 3719 0321250 248 6002 0591270 258 0606 082

PP-CNF

1150 310 13432 0181200 298 480 0411250 252 37 0871270 265 179 139

PP-LiBe

1200 276 1382 0521220 267 474 0811250 274 067 1491270 258 008 234

PP-Millad

1180 347 1945 0401200 250 914 0521250 193 115 2521270 205 005 480




5min

10min

15min

20min

25min















4 Conclusions






119888




Competing Interests


Acknowledgments


References









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Inte

nsity

5 10 15 20 25 30 35

CNTZN-iPP

2120579

(110) 120572(040) 120572

(130) 120572

Xc = 4347

(a)

Inte

nsity

5 10 15 20 25 30 35

CNFZN-iPP

2120579

Xc = 4351

(b)

Inte

nsity

5 10 15 20 25 30 35

LiBeZN-iPP

2120579

Xc = 4347

(c)

Inte

nsity

Millad

5 10 15 20 25 30 352120579

ZN-iPP

Xc = 4860

(d)











110

112

114

116

118

120

122

124

126

Concentration (wt)

MilladLiBe

CNFCNT

000 002 004 006 008 010

Crys

talli

zatio

n te

mpTc

(∘C)










119888









0001 111 111 117 1166001 110 116 119 1185005 111 123 1195 120010 124 125 120 1205


119888remained













0001 1 1 246 209001 2 15 307 283005 10 40 326 338008 26 49 346 351010 45 52 357 363






1198882max


1198881



1198791198882maxminus 1198791198881

(1)

where 119879119888NA



1198882max


1198882max


1198881



0

10

20

30

40

50

60

Nuc

leat

ing

effici

ency

()


MilladLiBe

CNFCNT








00

02

04

06

08

10

Relat

ive c

rysta

llini

ty (

)

Time (min)

PPCNTCNF

LiBeMillad

00 05 10 15 20 25 30 35 40

(a)

CNTCNFLiBe

MilladPP

2

2 3 4

1

1

0

0

minus1

minus1

minus2

minus2

minus3

minus3

minus4

minus5

minus6

ln (time)

ln(1

[minusln

minus120572

)](b)



120572 = 1 minus exp (minus119870119905119899)

1 minus 120572 = exp (minus119870119905119899)


minus ln (1 minus 120572) = 119870119905119899



(2)


Values of 119870 119899 and 11990512






Sample 119879119888[∘C] 119899 119870 119905

12[min]

PP

1150 258 017 171170 271 0052 321200 261 0002 821220 249 00018 105

PP-CNT

1150 284 7411 0171200 274 3719 0321250 248 6002 0591270 258 0606 082

PP-CNF

1150 310 13432 0181200 298 480 0411250 252 37 0871270 265 179 139

PP-LiBe

1200 276 1382 0521220 267 474 0811250 274 067 1491270 258 008 234

PP-Millad

1180 347 1945 0401200 250 914 0521250 193 115 2521270 205 005 480




5min

10min

15min

20min

25min















4 Conclusions






119888




Competing Interests


Acknowledgments


References









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




110

112

114

116

118

120

122

124

126

Concentration (wt)

MilladLiBe

CNFCNT

000 002 004 006 008 010

Crys

talli

zatio

n te

mpTc

(∘C)










119888









0001 111 111 117 1166001 110 116 119 1185005 111 123 1195 120010 124 125 120 1205


119888remained













0001 1 1 246 209001 2 15 307 283005 10 40 326 338008 26 49 346 351010 45 52 357 363






1198882max


1198881



1198791198882maxminus 1198791198881

(1)

where 119879119888NA



1198882max


1198882max


1198881



0

10

20

30

40

50

60

Nuc

leat

ing

effici

ency

()


MilladLiBe

CNFCNT








00

02

04

06

08

10

Relat

ive c

rysta

llini

ty (

)

Time (min)

PPCNTCNF

LiBeMillad

00 05 10 15 20 25 30 35 40

(a)

CNTCNFLiBe

MilladPP

2

2 3 4

1

1

0

0

minus1

minus1

minus2

minus2

minus3

minus3

minus4

minus5

minus6

ln (time)

ln(1

[minusln

minus120572

)](b)



120572 = 1 minus exp (minus119870119905119899)

1 minus 120572 = exp (minus119870119905119899)


minus ln (1 minus 120572) = 119870119905119899



(2)


Values of 119870 119899 and 11990512






Sample 119879119888[∘C] 119899 119870 119905

12[min]

PP

1150 258 017 171170 271 0052 321200 261 0002 821220 249 00018 105

PP-CNT

1150 284 7411 0171200 274 3719 0321250 248 6002 0591270 258 0606 082

PP-CNF

1150 310 13432 0181200 298 480 0411250 252 37 0871270 265 179 139

PP-LiBe

1200 276 1382 0521220 267 474 0811250 274 067 1491270 258 008 234

PP-Millad

1180 347 1945 0401200 250 914 0521250 193 115 2521270 205 005 480




5min

10min

15min

20min

25min















4 Conclusions






119888




Competing Interests


Acknowledgments


References









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






0001 1 1 246 209001 2 15 307 283005 10 40 326 338008 26 49 346 351010 45 52 357 363






1198882max


1198881



1198791198882maxminus 1198791198881

(1)

where 119879119888NA



1198882max


1198882max


1198881



0

10

20

30

40

50

60

Nuc

leat

ing

effici

ency

()


MilladLiBe

CNFCNT








00

02

04

06

08

10

Relat

ive c

rysta

llini

ty (

)

Time (min)

PPCNTCNF

LiBeMillad

00 05 10 15 20 25 30 35 40

(a)

CNTCNFLiBe

MilladPP

2

2 3 4

1

1

0

0

minus1

minus1

minus2

minus2

minus3

minus3

minus4

minus5

minus6

ln (time)

ln(1

[minusln

minus120572

)](b)



120572 = 1 minus exp (minus119870119905119899)

1 minus 120572 = exp (minus119870119905119899)


minus ln (1 minus 120572) = 119870119905119899



(2)


Values of 119870 119899 and 11990512






Sample 119879119888[∘C] 119899 119870 119905

12[min]

PP

1150 258 017 171170 271 0052 321200 261 0002 821220 249 00018 105

PP-CNT

1150 284 7411 0171200 274 3719 0321250 248 6002 0591270 258 0606 082

PP-CNF

1150 310 13432 0181200 298 480 0411250 252 37 0871270 265 179 139

PP-LiBe

1200 276 1382 0521220 267 474 0811250 274 067 1491270 258 008 234

PP-Millad

1180 347 1945 0401200 250 914 0521250 193 115 2521270 205 005 480




5min

10min

15min

20min

25min















4 Conclusions






119888




Competing Interests


Acknowledgments


References









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




00

02

04

06

08

10

Relat

ive c

rysta

llini

ty (

)

Time (min)

PPCNTCNF

LiBeMillad

00 05 10 15 20 25 30 35 40

(a)

CNTCNFLiBe

MilladPP

2

2 3 4

1

1

0

0

minus1

minus1

minus2

minus2

minus3

minus3

minus4

minus5

minus6

ln (time)

ln(1

[minusln

minus120572

)](b)



120572 = 1 minus exp (minus119870119905119899)

1 minus 120572 = exp (minus119870119905119899)


minus ln (1 minus 120572) = 119870119905119899



(2)


Values of 119870 119899 and 11990512






Sample 119879119888[∘C] 119899 119870 119905

12[min]

PP

1150 258 017 171170 271 0052 321200 261 0002 821220 249 00018 105

PP-CNT

1150 284 7411 0171200 274 3719 0321250 248 6002 0591270 258 0606 082

PP-CNF

1150 310 13432 0181200 298 480 0411250 252 37 0871270 265 179 139

PP-LiBe

1200 276 1382 0521220 267 474 0811250 274 067 1491270 258 008 234

PP-Millad

1180 347 1945 0401200 250 914 0521250 193 115 2521270 205 005 480




5min

10min

15min

20min

25min















4 Conclusions






119888




Competing Interests


Acknowledgments


References









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





5min

10min

15min

20min

25min















4 Conclusions






119888




Competing Interests


Acknowledgments


References









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials














4 Conclusions






119888




Competing Interests


Acknowledgments


References









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article effect of different nucleating agents...

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