Awasthi, S K

Bajpai, R

IACS Institutional Repository

Iiicliciii J. Phys. 77A(3), 233-236 (2003)$^  \  U P  A \Studies on microhardness, compatibility and thermal stability of poly(ethylmethacrylate) (PEMA) and poly(ethyleneoxide) (PEO)polyble^dsS K Awaslhi and Bajpai*Department of Post-Graduate Studies and Research in Physics, Rani Diirgawati University, Jabalpur 482 (KH, Madhya Pradesh, IndiaE'liiail ; ska l()(X)C«^ re#ffinail comR eceived  29  O ctohei 2()()I. a ccep ted  IH N ovem ber 2002Abstract . Microhardness study on polyblends of poly(ethylmethacrylaie) (PEMA) and poly(cihylcneoxidc) (PFiO) is carried out by Vtcker’s microhardness testing Thermal stability of this blend is investigated by Thermograviinetric analysis (TGA) and Dilterential iluTinal analysis (DI A). The decrease in the value of surface inicrohardiiess with increasing content of I^ HO in the blend reveals plasticization elicct The variation in thermal stability with increasing content of PEO is observed by TGA The variation in compatibility and crystallinity ol blend with increasing content of PEO is observed by DTA. Attempts have been made to correlate the results of microhardness and IGA-DTAKeywords : Polyblend, microhardness, TGA. DTA, thermal stability, plasticization, compatibility, crystallinity PACS Nos, 6I .41.+C, 62 20FC, 81 40 Gh. 81 4().Lm1. In troductionPolymers arc widely used in industry largely owing to their valuable mechanical properties. In recent years, attention has been focused on mixtures o f polymers i.e. polymer blends. Polymer blends are formed by mixing two or more polymers in common solvent. Polymer blends have better mechanical properties than their constituent polymers. By correctly choosing the polymers having different mechanical properties and chemical structures, one can obtain required SCI ot valuable properties.Now a days, lot o f attention has been devoted to the characterization o f  these po lym er b lends [1~5]. The characterization o f polym er blend means investigation of mutual compatibility o f constituent polymers, variation of ^1‘sicibility w ith  vary ing  com position  o f  constituen t polymers, structural changes induced by blending, variationmechanical properties, variation in thermal stability, in crystallinity etc,Corresponding AuthorThe blend system  presented here, com prises o f a amorphous polymer PEMA and a crystallizablc polymer PEG. 'Hic blend system with one of the components as crystallizablc, has interesting behaviour. The addition o f an amorphous polymer to a crystallizablc polymer can have rem arkab le effect on m isic ib ilily , p la s tic iza tio n  and crystallization behaviour of such polymer blends | 2 |.T hcrm ograv im clric  analysis (TG A ) is a v ersa tile  technique to study thermal degradation of polymers [6 ]. Knowledge gained from studies of polymer degradation may lead to more useful and stable polymers. TGA is a continuous process that involves the measurement of sample weight as the reaction  tem peratu re  is changed  by m eans o f a program m ed rate of heating 17], To study the therm al stability of PEMA : PEO blends, TGA has been utilized.Differential thermal analysis (DTA) is an important technique for understanding the structure, organization and properties o f polymer blends. DTA has been used for the© 2003 lACS234 S K Awasthi and R Rajpaideterm ination  of com patib ility  and incom patib ility  of polym er blends [8 -10], In general, com patible system  exhibits single glass transition temperature (7^) that falls between the 7^’s of the blend constituents. Compatibility is a representation o f how close a blend can approach the ultimate state of mixing. 7'hc lack o f compatibility leads to phase separation of* the components and ultimately poor mechanical properties. DTA curves have been also used to detect change in crystallinity of blends |111. DTA involves measurement of temperature difference (A7 ) between a sample and an inert reference material as the two arc being heated or cooled at a known (linear) rate 111 j. In the present investigation. DTA has been used to detect the change in compatibility and variation in cry.stallinity o f PEM A : PEO polyblend with varying composition o f PEO.M icrohardness testing has proved to be very popular for studying mechanical properties of polymers because o f its simplicity and non-dcstructivc nature ( 1 2 1 . In the present study. V icker’s microhardness testing has been used to detect the plasticization effect on PEM A : PEO blend and to study the effect o f load and com position ratio o f the two polymers on V icker’s m icrohardness number.2. Experimental details2.1. Materials :For the preparation of the blends, the commercially available polymers PEM A (Aldrich. USA) and PEO (BDH, UK) were used. P olym er g ranules w ere supplied by M /s Redox, Jabalpur. PEM A with very high m olecular weight grade and PEO having m olecular weight o f 30()0(K) were quoted by the manufacturer.2.2. Preparation of polyblend :The solution cast technique was utilized to prepare the blends o f the two polym ers PEM A and PEO, 'Fhc known amounts o f two polym ers were dissolved in benzene at 40 °C with constant stirring. A known quantity o f this hom ogeneous solution was poured in glass mould kept inside the oven whose temperature was controlled automatically. The solution was then allowed to evaporate at a drying tem perature of 40  °C for four hours. This yielded blend specim ens in the form of pellets o f size 6  cm^ and 0.4 cm thickness.2.3. Characterization and testing :Microhardness :The V ickcr’s hardness num ber {Hy) was determined with m h p l6 0  m icrohardness tester w ith a V icker’s diam ond pyramidal indentcr. having a square base and 136® pyramidal angle attached to an Carl Zeiss NU2 universal research microscope. Hy was calculated using the relation :„  I .8 5 4 X L , , ,---- kg /  m m ^.where L is the load in kg and d  is diagonal of indentation in mm. The load ranging from 10 to 100 g was apphe^ j gently at a steady rate. The time o f application of load was 30 seconds in each case. Several indentations were obtained at each load and the average hardness num ber was calculatedTGA and DTA :TGA and DTA studies o f the sam ples have been carried <hii with M ettler T oledo Instrum ent, Sw itzerland at RSi( N agpur U niversity, N agpur. The instrum ent here has a thcrmoanalyser which simultaneously record temperature and sample weight loss along with DTA curves. Simullancmr TGA and DTA patterns o f pure PEM A and polymer blend having 5 wt^> o f PEO, 25 wt% of PEO and 50 wF/r of ppo have been obtained.3. Re.sults and discussionTlie variation o f Hy with load ranging from 10 to 100  ^ i both the pure PEM A  and PEO  po lyb lend  samples \s illustrated in Mgurc I. It is evident from this figure thai ihi Hy value increases with load upto 40 and 50 g lor pure PEM A and PEM A : PEO poly blends respectively Beyond these loads. Hy tends to saturate. Further, the figure reveaK tha t the  m ic ro h a rd n ess  o f  sp ec im en s decreases wnii increasing content o f PEO in the polybicnd.10 ..Load in gFigure 1. Variation of H y with load for pure PEMA and PEMA polyblends.PhOThe increase in Hy with increasing load can be explained on the basis o f the strain hardening phenom enon [3 , 1 3 , 141. On applying load, the polym er is subjected to some strain h ard en in g . F in a lly , w hen  Hy v a lu e  ten d s  to become co n s tan t, the p o ly m er is c o m p le te ly  strain-hardened. The rate o f strain^hardening is greater at low load.s and decreases at higher loads. A lso it is evident that rate of strain- hardening decreases with increasing content o f PEO. decrease in the value o f  Hy with increasing content ot PEO suggests that PEO  acts as a plasticizer or softner for PEMAStudies on microhardness, compatibility and thermal stability etc 235The addition o f PEO leads to the reduction o f steric hindcrcnce between PEMA chain ntolecules, thus resulting in the decrease in the value of H yTGA-DTA traces for pure PEMA and the polyblend samples arc given in Figures 2-5. In the case of pure PEMA (Figure 2), thermal degradation starts at about 167°C andB.aIFigure 2. TGA-DTA pattern for pure PEMA..sFigure 3. TGA-DTA pattern for specimen having 5 weight % of PEO.“Itmt 5.2% weight loss occurs at 208“C. While in the case polyblend having 5 wt% of PEO (Figure 3), thermal <lcgradation begins little earlier around 153*C and only about ‘1.5% weight loss occurs at 175*C. For polyblend with 25 '*'1% of PEO (Figure 4), first decompottition begins at highest ‘^ ’nperature of id>out 205*C while little higher weight loss of about 8% takes place at about 237“C. The first ®ootnposition data for polyblend having 50 wt% of PEO(Figure 5) is almost similar to that of polyblend with 5 wt% of PEO sample, although here the % weight loss is about 5% which is slightly higher.*C \OX/ o t a V,, 0  0-oY.0 4.-0 t-tOA -1 0-«qoM ____ M _inla53H gi^S . TGA-DTA pattern for specimen having 50 weight % of PEO.The second decomposition in pure PEMA begins at about 338^C and almost complete decomposition (weight loss is about 89%) takes place at 387®C. For polyblend having 5 wt% of PEO, second decomposition begins at lower temperature of about 227®C; however, with lesser weight loss of about 65% takes place around 2S2°C. In the case of sample with 25 wt% of PEO, the second decomposition starts at higher temperature of about 282°C and about 72% weight loss occurs at 391 “C. For sample with 50 wt% o f PEO, second  decomposition initiates at lowest temperature of about 222°C while lowest weight loss of about 20% takes place up to 253°C.The samples with 5 wt% of PEO and that with 50 wt% of PEO, exhibits third decomposition also. In 5 wl% of PEO sample, it begins around 279*0 and about 59% weight loss occurs at 361“C place, while for sample with 50 wl% of PEO, third decomposition starts at higher temperature of 298°C and ends around 387*0 with about 53% weight loss.The decomposition data obtained from the TGA patterns reveal that thermal stability of polyblend samples depend upon the concentraton of PEO. Increased thermal stability is seen for blend specimens upto 25 wt% of PEO. For the blend having 50 wt% of PEO, thermal stability decreases. It is also evident from the TGA pattern of pure PEMA that thermal stability is somewhat more than that of polyblend samples having 5 and 50 wt% of PEO. The polyblends with 5 and 50 wt% of PEO show third decomposition, although there first and second decompositions begin at lower temperatures but the weight loss associated with first and second decompositions is lower than the pure PEMA. Although the polyblenid samples having 5 and 50 wt% of PEO thermally degrade at lower temperatures but there decomposition phenomenon is expanded over wide range of temperature in comparison to that of pure PEMA which exhibits sharper decomposition pattern.236 S K Awasthi and R BajpaiThe DTA patlerns for various blend specimens with 5, 25 and 50 wt% of PEO give the values of 7 , as 1 lO^C, I20“C, I30°C respectively. An increase in Tg with increasing crystallinity has been reported in the literature [ 15-17J. Thus, the crystallinity of PEMA : PEO polyblend increases with increasing concentration of PEO in polyblend. It is also evident from the DTA patterns that there is a single value of Tg. thus the constituents PEMA and PEO form compatible blends in the studied weight proportions of the two polymers. Also the occurrence o f single Tg indicates the phase homogeneity and existence of single phase in the blend system.4. ConclusionThe microhardness and TGA-DTA studies provide effective tools for the characterization of PEMA : PEO polyblend.The increasing content of PEO in PEM A: PEO polyblend decreases the microhardness with added advantage o f  crystallizability and increased thermal stability. Increased crystallinity and better thermal stability with lower values of microhardness have been seen for polyblcnds having higher content of PEO. Thus PEM A: PEO forms compatible blend with a single phase system.AcknowMgmentAuthors arc thankful to R egional Sophisticated  Instrumentation Centre (RSfC), Nagpur University, Nagpur for providing TGA-DTA facilities.Referenceit[1 ]  S Cim m inQ, E  Martuscelli, C  Silvestre. M Canetti, C  Je i ,|.and A  Seves J  Polyni Sci. 2 7  1781 (1989) **''[2) S H  A h n , J H  A n , D  S Le e  and S C  K im  J. Polym. St i B3( k i ,(1993) 'P i  R  Bajpai, P Agrawal and S C  Daft / . P o/ym n  T e m i;  i j  m.(1994)[4] R  Bajpai, R Paliwal and S C  D a li J .  Polym. M nta  J3 i|(.j(1996)[5] J Slraka, P .Schmidt, J  D yba l, B  .Schneider and J  Spevacck Po/v,,,,., 36 114 7  (199.S)[6] P  P  Lizyin o l and .Sabu Thoma.s Polymer DeKnidaium und .Siahi,,. 4 1 .59 (1993)[71 N o rb e rt M  B ik a le s  (e d .)  C ln ira c te r iz a lio n  o\ Pohniei. Encyvlopedm Reprint.^ (N e w  Y o rk  : Wiley-tnlerscicncc) p 2v  (1 9 7 1 )|8| D  S Hubbell and .S L  Cooper J. Appl. Polym. 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Studies on Microhardness, Compatibility and Thermal Stability of Poly(ethylmethacrylate) (PEMA) and Poly(ethyleneoxide) (PEO) Polyblends

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Studies on Microhardness, Compatibility and Thermal Stability of Poly(ethylmethacrylate) (PEMA) and Poly(ethyleneoxide) (PEO) Polyblends

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