Research Article Study of Natural and Accelerated ...

Research ArticleStudy of Natural and Accelerated Weathering onMechanical Properties of Antioxidants Modified Low DensityPolyethylene Films for Greenhouse

Othman Al Othman12 Shan Faiz1 and Muhammad Abduh Tuasikal1

1 Chemical Engineering Department King Saud University PO Box 800 Riyadh 11421 Saudi Arabia2Deanship of Graduate Studies The Saudi Electronic University Riyadh Saudi Arabia

Correspondence should be addressed to Shan Faiz sfaizksuedusa

Received 16 March 2014 Revised 15 July 2014 Accepted 29 July 2014 Published 20 August 2014

Academic Editor Geoffrey R Mitchell

Copyright copy 2014 Othman Al Othman et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Natural and accelerated weatherings were studied to inspect the effect of antioxidants to protect low-density polyethylene (LDPE)films for commercial application as greenhouse covering materials in Saudi Arabia In this investigation six different formulationsof LDPE film with incorporation of antioxidants were prepared and compared with neat LDPE The samples were extruded andblown into a film using twin-screw extruder and film blowing machine The LDPE films were exposed for outdoor weathering inRiyadh during the period of 90 days (mid of June to mid of September) while the accelerated tests were performed by Weather-Ometer The film having 02 wt Alkanox-240 (AN-02) stabilizers showed the highest tensile strength among all samples duringnatural and 100-hour accelerated weathering (109MPa and 218MPa resp) The best elongation at break was witnessed in 02Good-rite antioxidants which were 64 in natural weathering however 05 Good-rite antioxidants showed 232 in acceleratedweathering The film having 05 wt Good-rite 3114 (GR-05) antioxidant could withstand 70 days during natural exposure beforethe tensile strength values were reduced to 23rd of the initial The present study suggested that the addition of antioxidants Good-rite Anox and Alkanox can improve the mechanical strength filmrsquos life effectiveness and stability and they are suitable to beincorporated in LDPE for commercial greenhouse films

1 Introduction

Greenhouses are known to provide most suitable conditionsfor production as the crops are being controlled and lookedafter under suitably controlled environment that is bymaintaining basic requirements for agriculture for examplewater fertilizers seeds and plant protection chemicals Itis known that greenhouses are covered with transparentmaterial that transmits visible light (400ndash700 nm) which isthe major source of energy for photosynthesis [1] In thelast decades the increased research towards greenhouses hassignificantly increased the involvement of plastics for use as acover material [2]

Low-density poly ethylene (LDPE) being of light weighttransparent economical and of robust mechanical strengthhas dominated the use of plastic films as greenhouse coveringmaterials However the greenhouse materials are subjected

to numerous environmental factors that lead to chemicalandor physical degradation It is well depicted in literaturethat degradation of LDPE is enhanced byUV radiationwhichtransfers its energy to polymer molecules causing them to beenergized and subject to oxidation [3]

Researchers have aimed to enhance the stability of LDPEfilms to make it more effective for greenhouse cover anda number of antioxidants and UV stabilizers have beenreported in the literature [4ndash6] Mashael [7] studied theeffect of talc (10) with PP and reported enhanced stressat break elongation at break and Youngrsquos modulus Xueet al [8] developed aspen fiber-polypropylene compositesand studied mechanical properties at 4∘C and 40∘C Theyreported increase in tensile moduli flexural moduli andflexural strength as the wood fiber content increased inthe composites The tensile strength decreased as the fibercontent increased

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2014 Article ID 543930 5 pageshttpdxdoiorg1011552014543930

2 International Journal of Polymer Science

Table 1 Formulations of LDPE resin with additives percentages andfilms codes

Type of additives Code wtGood-rite 3114 antioxidant GR-02 02

GR-05 05GR-20 20

Anox 20 AN-02 02Alkanox 240 AL-02 02AnoxAlkanox ANAL-0101 0101

The effects of natural and accelerated weathering onpolyethylene-based films containing commercially availablepink yellow and white organic pigments and a UV absorberof the benzophenone type were investigated by Michalkovaet al [9] They concluded that all films experienced increasein viscosity and decrease in tensile strength and elongationat break in natural weathering Ojeda et al [10] comparedHDPE LLDPE (linear low-density polyethylene) and iso-tactic polypropylene (PP) containing antioxidant They leftthe samples in natural weathering for a year to observethe structural changes and its impact on the thermal andmechanical propertiesThey found that HDPELLDPE blendand PP degraded faster than HDPE and LLDPE individuallyand concluded that presence of tertiary carbon atoms was themain cause for this result

In the present study we used Good-rite 3114 antioxi-dant Anox 20 and Alkanox 240 at various concentrationsand blends to investigate their behavior on the mechanicalproperties of LDPE films under natural and acceleratedweathering

2 Materials

Low-density polyethylene (LDPE HP0322N) film blowinggrade was supplied by SABIC Saudi Arabia with density0922 gcm3 and melt flow index 031 g10min It containsno slip and antiblock additives HP0322N offers outstandingtoughness and good optical properties and is suitable tobe processed via extrusion and conventional blown filmtechnique

In this investigation LDPE filmswith six different antiox-idants were prepared using film blowing and their behaviorwas compared with neat LDPE The formulations are givenin Table 1

21 Preparation of LDPE Films The LDPE pellets wereextruded using twin-screw extruder and then blown into afilm using film blowing machine LDPE pellets with additiveblends were first melt-mixed in a twin-screw corotatingextruder (Farrel Limited FTX 20 US)The conditions were asfollows Barrel zone temperatures were 180∘C 190∘C 200∘C210∘C 220∘C and 230∘C extruder speed was set at 14 rpmand melt pressure was 22 bar

The materials were fed into the extruder from hopperwhich runs into the barrel containing the rotating screwThis screw mixes compresses and moves the polymer as itchanges from solid granules to a viscous melt The screw

Table 2 The conditions of Weather-Ometer chamber

Condition ValueBlack panel temperature 75∘CChamber temperature 58∘CRelative humidity 5Irradiance 340 nm 06Wm2

diameter is 26mm with LD ratio of 35 The extrudate wascooled in a water bath at about 20∘C pelletized and was leftair-dried over 24 hours In the next step the material was fedin the film blowing machine

The film blowing extrusion process began with plasticsin pellet form being dropped into the extruder from thehopper The extruder conveys the plastics forward using arotating screw The screw melts the plastic pellets by bothfriction heating and outside heaters around the barrel Oncethematerial is molten it is fed upwards through a circular dieto form a hollow plastic tube filled with a desired amount ofair

The plastic tube was continuously brought upward fromthe tensile force (pull) of nip rollers above the die The niprollers are twowheels like steam rollers which are several feetabove the dieThe nip rollers are pressured together to form apinch-off on the bubble keeping a constant air volume belowand flattening the plastic out In film blowing machine barreltemperatures were 200∘C 180∘C and 150∘C winder speedwas 270 rpm and extruder speed was set at 450 rpm

22 Weathering of LDPE Films

221 NaturalWeathering Test TheLDPE films were exposedto outdoor weathering on the roof of the college of engineer-ing King Saud University Riyadh Saudi Arabia (46∘ 471015840 Elongitude and 24∘ 391015840N latitude) The LDPE films wereexposed to natural weathering The sample sizes were 6 cm times11 cm and were assembled on a steel cage at a 35∘ angle facingthe south (Figure 1)

This natural weatheringwas carried out during the periodof summer season for 90 days from mid of June to mid ofSeptember 2012 The temperature during the day and nightranged between 30 and 45∘C and between 25 and 31∘Crespectively The wind speed was around 20 to 30 kmhourand humidity was around 10 to 15 [11]

222 Accelerated Weathering Test With outdoor weatheringtest accelerated weathering test for 0 75 and 100 hours wascarried out using accelerated weathering apparatus (AtlasCi5000 Xenon Weather-Ometer USA) LDPE films withgood mechanical behavior (size 7 cm times 15 cm) were clampedin aluminum rack The conditions in the chamber are tabu-lated in Table 2

3 Characterizations

31 Mechanical Properties The tensile properties were mea-sured through the conventional uniaxial tension test ona Hounsfield H100 KS series tensile testing machine The

International Journal of Polymer Science 3

Before weathering After weathering After weathering

Figure 1 Natural (outdoor) weathering of LDPE films

dumbbell-shaped specimens ASTM D638 of all materialswere tested at room temperature at crosshead speed of50mmminThe samples were held between two clampsTheupper clamp was connected to a cross-head which movesupwards at a preprogrammed rate to apply tension to thesample The values were taken from the mean of 3 runs forall cases

4 Results and Discussion

41 Preweathering Characterization of LDPE Films NeatLDPE (40 120583m) showed the highest elongation at break at246 as shown in Figure 2(a) The elongations at break ofother two films AN-02 and AL-02 (with same thicknessof 40 120583m) containing different additives are lower than neatLDPE For additive filled LDPE elongation at break wasabout 215 for the blends ANAL-0101 (film thickness70 120583m) The comparison between neat LDPE and antioxi-dants incorporated films is represented in Figure 2(b) NeatLDPE film supersedes the rest with a value of 38MPa Amongthe rest AN-02 showed tensile strength of 33MPa and GR-02 of 30MPa which suggests that they are good coveringmaterials The elastic moduli for various antioxidants areshown in Figure 2(c) AN-02 showed the best modulus(426MPa) followed by GR-02 with a value of 301MPaAll other samples had considerably high values with theexception of GR-05

Table 3 Tensile strength of LDPE films under natural and acceler-ated weathering

SampleTensile strength (MPa)

Accelerated weathering Natural weathering0 h 75 h 100 h 0 day 90 days

Neat LDPE 383 196 153 383 103GR-02 297 231 209 297 63GR-05 162 127 98 162 87GR-20 271 84 53 271 76AN-02 337 253 218 337 109AL-02 263 205 130 263 27

42 Postweathering Characterization of LDPE Films Table 3tabulated the tensile strength change during accelerated andnatural weathering respectively The increase in weatheringtime in both cases showed reduction in the tensile strengthThe least decrease in tensile strength was obtained in AN-02in 90 days natural weathering whose strength was reducedfrom 337 to 109MPa Similar sample showed the best resultfor the 100 h accelerated weathering

The elongation at break of postweathered samples ismen-tioned in Table 4 GR-02 showed the maximum elongationand its value was raised to 232 from the original 898


0

50

100

150

200

250

Elon

gatio

n (

)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(a)

0

10

20

30

40

Tens

ile st

reng

th (M

Pa)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(b)

50

150

250

350

450

Elas

tic m

odul

us (M

Pa)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(c)

Figure 2 Elongation at break (a) tensile strength (b) and elastic modulus (c) for LDPE films

Except forGR-02 no other formulation showed considerablerise in this regard

Table 5 illustrates elastic modulus of plastic films undernatural and accelerated weathering This table exhibits fineresults with reduction in elastic modulus GR-05 showedthe best trend and even after weathering it shows a rise inthe elastic modulus thus providing better stability to thematrix under harsh conditions The elastic modulus wasincreased from 918MPa to 963MPa (natural weathering)and to 1389Mpa (accelerated weathering) This intensifiedthe fact that incorporation of 05 Good-rite antioxidantprovides better stability than other formulations This resultis supported with 119905

23discussed in the next section

It can be seen from Figure 3 that the weathering periodfor the reduction to 23rd of the initial value of tensilestrength 119905

23 of tested films under accelerated condition

is approximately 2 days whereas for natural weathering ittook around 17 days This result means that the acceleratedtest method is about 9 times faster than natural exposure inRiyadh (JunendashSeptember)

LDPE films with 02 Anox antioxidant take about 20days to reach 23rd of the initial value of tensile strengthunder natural weathering while this filmwithout antioxidantrequires about 17 days For LDPE film containing 05Good-rite antioxidant 119905

23of the weathered film exposed to natural

weather is approximately 70 days So the usage life of AN-02and GR-05 films is approximately 12 and 41 times greaterthan the life of neat LDPE film respectively

Table 4 Elongation at break of LDPE films under natural andaccelerated weathering

SampleElongation at break ()


Neat LDPE 2460 1812 916 3057 63GR-02 898 1716 2320 3639 178GR-05 1206 1249 1380 918 640GR-20 1014 608 369 2580 388AN-02 1164 1712 972 4256 163AL-02 1694 1198 834 2419 160ANAL-0101 2150 3624 4180 2113 129

Good-rite antioxidants were used at different concen-trations At 20 wt its 119905

23under natural weathering is 18

days while this film without antioxidant takes about 17 daysIt means that 20 wt of Good-rite antioxidant is about 11times faster than films without antioxidant The results alsoshow that GR-05 is more effective in durability than 02 wtand 20wt This weight that is 05 enhances stability(41 times faster) whereas the other two weights do notThe threshold of Good-rite antioxidant that provides goodeffectiveness is probably 05 wt


Table 5 Elastic modulus of LDPE films under natural and acceler-ated weathering

SampleElastic modulus (MPa)



0

10

20

30

40

50

60

70

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

Natural weatheringAccelerated weathering

Num

ber o

f day

s

01

01

Figure 3 Comparison of 11990523

by natural and accelerated weatheringfor LDPE films

5 Conclusion

Theweathering behavior of films of low-density polyethyleneblends containing three different antioxidants and theirblends was analyzed by subjecting the films to both naturaland artificial weathering exposureThefilmwithAnox (02)showed the maximum tensile strength and elastic modulusamong all formulations in preweathering conditions Inpostweathering results AN-02 showed better stability thanall other films for both natural and outdoor exposure Thereduction of tensile strength to 23rd of the initial valuewas best obtained for GR-05 which was 70 days for naturalexposure The elastic modulus after natural and acceleratedweathering showed that GR-05 provided great stability tothe polymer matrixThe results showed that incorporation ofGoodrite antioxidant with 05 content and Anox with 02enhanced the mechanical properties of LDPE and they arebest suited to be used as greenhouse covering

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors acknowledge the College of EngineeringResearch Center and Deanship of Scientific Research at KingSaud University in Riyadh for the financial support to carryout the research work reported in this paper

References

[1] D Briassoulis D Waaijenberg J Gratraud and B von EslnerldquoMechanical properties of covering materials for greenhousespart 1 general overviewrdquo Journal of Agricultural EngineeringResearch vol 67 no 2 pp 81ndash96 1997

[2] N T Dintcheva F P La Mantia D Acierno et al ldquoChar-acterization and reprocessing of greenhouse filmsrdquo PolymerDegradation and Stability vol 72 no 1 pp 141ndash146 2001

[3] D Briassoulis and E Schettini ldquoAnalysis and design of low-density polyethylene greenhouse filmsrdquo Biosystems Engineeringvol 84 no 3 pp 303ndash314 2003

[4] P A Dilara and D Briassoulis ldquoDegradation and stabilizationof low-density polyethylene films used as greenhouse coveringmaterialsrdquo Journal of Agricultural Engineering Research vol 76no 4 pp 309ndash321 2000

[5] S Bualek K Suchiva S Boonariya and B Ratana-ArakulldquoAging of low density polyethylene films for agricultural use inThailandrdquo Journal of the Science Society of Thailand vol 17 pp103ndash122 1991

[6] A A Basfar K M Idriss Ali and S M Mofti ldquoUV stability andradiation-crosslinking of linear low density polyethylene andlow density polyethylene for greenhouse applicationsrdquo PolymerDegradation and Stability vol 82 no 2 pp 229ndash234 2003

[7] AS Mashael ldquoStudy of the effect of weathering in natural envi-ronment on polypropylene and its composites morphologicaland mechanical propertiesrdquo International Journal of Chemistryvol 3 pp 129ndash141 2011

[8] Y Xue D R Veazie C Glinsey M F Horstemeyer andR M Rowell ldquoEnvironmental effects on the mechanical andthermomechanical properties of aspen fiber-polypropylenecompositesrdquo Composites Part B Engineering vol 38 no 2 pp152ndash158 2007

[9] D Michalkova J Pospısil I Fortelny et al ldquoRestabiliza-tion of the aging resistance of compatibilized blends of pre-aged low density polyethylene and high-impact polystyrene(LDPEHIPS)rdquo Polymer Degradation and Stability vol 94 no9 pp 1486ndash1493 2009

[10] T Ojeda A Freitas K Birck et al ldquoDegradability of linearpolyolefins under natural weatheringrdquo Polymer Degradationand Stability vol 96 no 4 pp 703ndash707 2011

[11] httpwwwpmegovsaenccasp

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 Formulations of LDPE resin with additives percentages andfilms codes

Type of additives Code wtGood-rite 3114 antioxidant GR-02 02

GR-05 05GR-20 20

Anox 20 AN-02 02Alkanox 240 AL-02 02AnoxAlkanox ANAL-0101 0101

The effects of natural and accelerated weathering onpolyethylene-based films containing commercially availablepink yellow and white organic pigments and a UV absorberof the benzophenone type were investigated by Michalkovaet al [9] They concluded that all films experienced increasein viscosity and decrease in tensile strength and elongationat break in natural weathering Ojeda et al [10] comparedHDPE LLDPE (linear low-density polyethylene) and iso-tactic polypropylene (PP) containing antioxidant They leftthe samples in natural weathering for a year to observethe structural changes and its impact on the thermal andmechanical propertiesThey found that HDPELLDPE blendand PP degraded faster than HDPE and LLDPE individuallyand concluded that presence of tertiary carbon atoms was themain cause for this result

In the present study we used Good-rite 3114 antioxi-dant Anox 20 and Alkanox 240 at various concentrationsand blends to investigate their behavior on the mechanicalproperties of LDPE films under natural and acceleratedweathering

2 Materials

Low-density polyethylene (LDPE HP0322N) film blowinggrade was supplied by SABIC Saudi Arabia with density0922 gcm3 and melt flow index 031 g10min It containsno slip and antiblock additives HP0322N offers outstandingtoughness and good optical properties and is suitable tobe processed via extrusion and conventional blown filmtechnique

In this investigation LDPE filmswith six different antiox-idants were prepared using film blowing and their behaviorwas compared with neat LDPE The formulations are givenin Table 1

21 Preparation of LDPE Films The LDPE pellets wereextruded using twin-screw extruder and then blown into afilm using film blowing machine LDPE pellets with additiveblends were first melt-mixed in a twin-screw corotatingextruder (Farrel Limited FTX 20 US)The conditions were asfollows Barrel zone temperatures were 180∘C 190∘C 200∘C210∘C 220∘C and 230∘C extruder speed was set at 14 rpmand melt pressure was 22 bar

The materials were fed into the extruder from hopperwhich runs into the barrel containing the rotating screwThis screw mixes compresses and moves the polymer as itchanges from solid granules to a viscous melt The screw

Table 2 The conditions of Weather-Ometer chamber

Condition ValueBlack panel temperature 75∘CChamber temperature 58∘CRelative humidity 5Irradiance 340 nm 06Wm2

diameter is 26mm with LD ratio of 35 The extrudate wascooled in a water bath at about 20∘C pelletized and was leftair-dried over 24 hours In the next step the material was fedin the film blowing machine

The film blowing extrusion process began with plasticsin pellet form being dropped into the extruder from thehopper The extruder conveys the plastics forward using arotating screw The screw melts the plastic pellets by bothfriction heating and outside heaters around the barrel Oncethematerial is molten it is fed upwards through a circular dieto form a hollow plastic tube filled with a desired amount ofair

The plastic tube was continuously brought upward fromthe tensile force (pull) of nip rollers above the die The niprollers are twowheels like steam rollers which are several feetabove the dieThe nip rollers are pressured together to form apinch-off on the bubble keeping a constant air volume belowand flattening the plastic out In film blowing machine barreltemperatures were 200∘C 180∘C and 150∘C winder speedwas 270 rpm and extruder speed was set at 450 rpm

22 Weathering of LDPE Films

221 NaturalWeathering Test TheLDPE films were exposedto outdoor weathering on the roof of the college of engineer-ing King Saud University Riyadh Saudi Arabia (46∘ 471015840 Elongitude and 24∘ 391015840N latitude) The LDPE films wereexposed to natural weathering The sample sizes were 6 cm times11 cm and were assembled on a steel cage at a 35∘ angle facingthe south (Figure 1)

This natural weatheringwas carried out during the periodof summer season for 90 days from mid of June to mid ofSeptember 2012 The temperature during the day and nightranged between 30 and 45∘C and between 25 and 31∘Crespectively The wind speed was around 20 to 30 kmhourand humidity was around 10 to 15 [11]

222 Accelerated Weathering Test With outdoor weatheringtest accelerated weathering test for 0 75 and 100 hours wascarried out using accelerated weathering apparatus (AtlasCi5000 Xenon Weather-Ometer USA) LDPE films withgood mechanical behavior (size 7 cm times 15 cm) were clampedin aluminum rack The conditions in the chamber are tabu-lated in Table 2

3 Characterizations

31 Mechanical Properties The tensile properties were mea-sured through the conventional uniaxial tension test ona Hounsfield H100 KS series tensile testing machine The














0

50

100

150

200

250

Elon

gatio

n (

)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(a)

0

10

20

30

40

Tens

ile st

reng

th (M

Pa)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(b)

50

150

250

350

450

Elas

tic m

odul

us (M

Pa)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(c)























0

10

20

30

40

50

60

70

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-


Num

ber o

f day

s

01

01



5 Conclusion




Acknowledgments


References



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















0

50

100

150

200

250

Elon

gatio

n (

)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(a)

0

10

20

30

40

Tens

ile st

reng

th (M

Pa)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(b)

50

150

250

350

450

Elas

tic m

odul

us (M

Pa)

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-

01

01

(c)























0

10

20

30

40

50

60

70

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-


Num

ber o

f day

s

01

01



5 Conclusion




Acknowledgments


References



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








0

10

20

30

40

50

60

70

Nea

tLD

PE

GR-

02

GR-

05

GR-

20

AN

-02

AL-

02

AN

AL-


Num

ber o

f day

s

01

01



5 Conclusion




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 Study of Natural and Accelerated ...

Documents

Transcript of Research Article Study of Natural and Accelerated ...