Micro-hardness of surface layer of irradiated polypropylene

Mic o-ha dness o su ace laye o i adia ed polyp opylene Da id Manasa Tomas Ba a Uni e si y in Zlin, TGM 5555, 760 01 Zlin, Czech Republic , Ma in O sik, Mi osla Manas, Michal S anek, Lenka Gajzle o a, Ma in Mize a, Libo Gabko and Lenka Hylo a Abs ac . Using high doses o be a adia ion o polyp opylene (PP) and i s in luence on he changes o mic omechanical p ope ies o su ace laye has no been s udied in de ail so a . The specimens o PP we e made by injec ion moulding echnology and i adia ed by high doses o be a adia ion (0, 33, and 66 kGy). The changes in he mic os uc u e and mic omechanical p ope ies o su ace laye we e e alua ed using WAXS and ins umen ed mic oha dness es . The esul s o he measu emen s showed conside able inc ease in mic omechanical p ope ies (inden a ion ha dness, inden a ion elas ic modulus) when high doses o be a adia ion a e used. Keywo ds: polyp opylene (PP), mic oha dness, mic omechanical p ope ies, su ace laye , β-i adia ion, WAXS. 1 In oduc ion Ins umen ed inden a ion has been in use al eady o se e al decades, as a echnique o p obe mechanical p ope ies o small olumes o ma e ials [1] and [2]. In me als, in which he echnique was i s applied, he echnique allows o p obe se e al mac oscopic p ope ies, like ha dness, Young modulus, yield s eng h, s ain ha dening exponen , among o he s [1-6]. I adia ion o a polyme by di e en adia ions leads o se e al physicochemical changes, a ew o which include scissioning and o c osslinking, ca boniza ion, conjuga ion, oxida ion, c ea ion o de ec s, gene a ion o low molecula weigh agmen s and e olu ion o gases. These changes induce conside able modi ica ions in mechanical, elec ical, he mal and op ical p ope ies o polyme s and a e quali a i ely o quan i a i ely based on p ope ies o adia ion and he polyme . Iso ac ic polyp opylene (iPP) is a commodi y polyme wi h he semi-c ys alline s uc u e which is e y complex and depends s ongly on he mal his o y and p ocessing condi ions. Iso ac ic polyp opylene can c ys allize in o 3 phases: α-phase is he mos s able and he mos known. The c ys als a e monoclinic. Be a phase is me as able and he c ys als a e hexagonal -phase is mainly ound in block PP copolyme s and can be gene a ed by addi ion o speci ic nuclea ing agen s. This phase was disco e ed by Padden and Kei h in 1953 and can be imp o ed by c ys alliza ion be ween 130 and 132 °C o by o ien a ion wi h high shea o h ough addi ion o speci ic nuclea ing agen s. P esence o -phase in PP homopolyme gene ally inc eases duc ili y in he inished pa s. Maximum e ec is obse ed a 65 % o be a-phase. Gamma phase - his phase is also me as able wi h iclinic c ys als. This o m is no a Co esponding au ho : dmanas@ .u b.cz In e na ional Con e ence on Inno a i e Ma e ial Science and Technology (IMST 2016) © 2016. The au ho s – Published by A lan is P ess 130 e y amilia bu appea s mainly in low molecula weigh polyp opylene by c ys alliza ion a e y high p essu e and e y low cooling a e [1-7]. 2 Expe imen al 2.1 Ma e ial and me hods Fo his expe imen polyp opylene (homopolyme ) Moplen HP3175 LyondellBasell company was used. Polyp opylene (PP) Moplen HP3175 is sui able o injec ion moulding applica ions and can also be used in echnical compounds as a base esin. I has a high mel low a e and i is supplied in pelle ized o m wi h densi y 0.9 g cm−3, wi h high c ys allini y and high s i ness. Mel low index was measu ed (230 °C/2.16 kg) 40 g/10 min. The ma e ial does no con ain a special c oss-linking agen TAIC— iallylisocyanu a e, which should enable subsequen c oss-linking by ionizing β- adia ion. I adia ion was ca ied ou in he company BGS Be a Gamma Se ice GmbH & Co, KG, Ge many wi h he elec on ays, elec on ene gy 10 MeV, doses minimum o 0, 33 and 66 kGy on ai he ambien empe a u e. The samples we e made using he injec ion molding echnology on he injec ion moulding machine A bu g All ounde 420C. P ocessing empe a u e 190–230 °C, mold empe a u e 40 °C, injec ion p essu e 80 MPa, injec ion a e 50 mm/s. [7-9] 2.2 Mic o-inden a ion es Mic o-inden a ion es was done using a Mic o Combi Tes e , CSM Ins umen s (Swi ze land) acco ding o he CSN EN ISO 14577. Load and unload speed was 1 N/min. A e a holding ime o 90 s a maximum load 0.5 N he specimens we e unloaded. The specimens we e glued on me allic sample holde s. Poisson’s a io (ν) o he polyme was 0.3. The inden a ion ha dness (HIT) was calcula ed as maximum load (Fmax) o he p ojec ed a ea o he ha dness imp ession (Ap acco ding o: [7-10]. p IT A F H max = (1) 2.3 Resul s and discussion The de elopmen o mic omechanical p ope ies o i adia ed polyp opylene was cha ac e ized by he ins umen ed es o mic oha dness (HIT), as can be seen in Fig. 1. The lowes alues (94 MPa) o inden a ion ha dness we e ound on non-i adia ed polyp opylene, while he highes alue o inden a ion ha dness (101 MPa) was measu ed a 66 kGy adia ion dose. The alues (100 MPa) o inden a ion ha dness we e ound on polyp opylene i adia ed wi h adia ion dose o 33 kGy adia ion dose. The inc ease o inden a ion ha dness a 66 kGy adia ion dose was by 7 % compa ed o he non-i adia ed polyp opylene. Simila de elopmen was eco ded o mic os i ness o specimens ep esen ed by he elas ic modulus o inden a ion (EIT) illus a ed in Fig. 2. The esul s o measu emen s show clea ly ha he lowes alues o mic os i ness we e measu ed on he polyp opylene (1.92 GPa) i adia ed wi h adia ion dose o 33 kGy, while he highes alues we e eached in polyp opylene i adia ed by 66 kGy dose (2.03 GPa). Lowe alue (1.93 MPa) o mic os i ness, we e ound on non-i adia ed polyp opylene. A dec ease o mic os i ness (5 %) was eco ded a he adia ion dose o 66 kGy compa ed o he non-i adia ed polyp opylene. In e na ional Con e ence on Inno a i e Ma e ial Science and Technology (IMST 2016) © 2016. The au ho s – Published by A lan is P ess 131 Figu e 1. Inden a ion ha dness s. i adia ion doses. Figu e 2. Inden a ion elas ic modulus EIT. O he impo an ma e ial pa ame e s ob ained du ing he mic o-ha dness es we e elas ic and plas ic de o ma ion wo k. The mechanical wo k W o al induced by he inden a ion is only pa ly consumed as plas ic de o ma ion wo k Wplas . Du ing he emo al o he es o ce he emaining pa is se ee as wo k o he elas ic e e se de o ma ion Welas . The highes alues o plas ic de o ma ion wo k we e ob ained o non-i adia ed polyp opylene. The highes alues o elas ic de o ma ion wo k we e ob ained o polyp opylene i adia ed wi h adia ion dose o 66 kGy. The lowes alues o Wel we e ob ained o polyp opylene i adia ed wi h dose o 33 kGy. The highes alues o plas ic de o ma ion wo k (Wpl) we e ob ained o polyp opylene i adia ed wi h adia ion dose o 66 kGy. The lowes alues o Wpl we e ob ained o polyp opylene i adia ed wi h dose o 0 kGy. Radia ion o specimens caused lowe alues o plas ic de o ma ion wo k which is in Fig. 4. Ve y impo an alues we e ound o inden a ion c eep. Fo ma e ials which c eep as polyme s, a basic calcula ion o ha c eep can be measu e du ing a pause a he maximum o ce. The c eep is he ela i e change o he inden a ion dep h when he es o ce is kep cons an measu ed by ins umen ed es o mic oha dness showed (Fig. 3) ha he lowes c eep alues we e measu ed on non-i adia ed polyp opylene (10.5 %), while he highes c eep alue was ound in polyp opylene i adia ed by 66 kGy dose (11.3 %). The c eep inc ease by 9 % as a esul o adia ion, which ep esen s a conside able dec ease o su ace es ing laye ’s mechanical p ope ies In e na ional Con e ence on Inno a i e Ma e ial Science and Technology (IMST 2016) © 2016. The au ho s – Published by A lan is P ess 132 Figu e 3. Inden a ion c eep CIT. Figu e 4. De o ma ion wo k s. i adia ion dose. Highe adia ion dose does no in luence signi ican ly he mic o-ha dness alue. An inden a ion ha dness inc ease o he su ace laye is caused by i adia ion c oss-linking o he es ed specimen. A close look a he mic o-ha dness esul s e eals ha when he highes adia ion doses a e used, mic o-ha dness dec eases which can be caused by adia ion induced deg ada ion o he ma e ial. 3 Conclusions The expe imen al s udy deals wi h he e ec o modi ica ion o he su ace laye by i adia ion c oss-linking on he p ope ies o he su ace laye o polyp opylene. Polyp opylene was modi ied by be a i adia ion a doses o 0, 33 and 66 kGy. The changes o mic omechanical p ope ies we e ound a he adia ion dose o 66 kGy o inden a ion ha dness (which inc eased by 7%) compa ed o he non-i adia ed polyp opylene. Imp o emen o mechanical p ope ies in mic o and mac o scale o adia ed polyp opylene has a g ea signi icance also o indus y. The modi ied polyp opylene shi s o he g oup o ma e ials which ha e conside ably be e p ope ies. I s mic omechanical p ope ies make polyp opylene ideal o a wide applica ion in he a eas whe e highe esis ance o wea , sc a ch a e equi ed. In e na ional Con e ence on Inno a i e Ma e ial Science and Technology (IMST 2016) © 2016. The au ho s – Published by A lan is P ess 133 Acknowledgmen s This wo k was suppo ed by he Minis y o Educa ion, You h and Spo s o he Czech Republic wi hin he Na ional Sus ainabili y P og amme p ojec No. LO1303 (MSMT-7778/2014) and also by he Eu opean Regional De elopmen Fund unde he p ojec CEBIA-Tech No. CZ.1.05/2.1.00/03.0089 and he in e nal g an o TBU in Zlin No. IGA/FT/2016/010 unded om he esou ces o speci ic uni e si y esea ch and by he Minis y o Educa ion, You h and Spo s o he Czech Republic. Re e ences 1. M. O sik, D. Manas, M. Manas, M. S anek, M. H ibo a, K. Kocman, D. Samek: I adia ed Polyp opylene S udied by Mic oha dness and WAXS, Chemicke lis y, 106 (2012), 507-510. 2. J. Gheysa i e al., The e ec o high-ene gy elec on beam on mechanical and he mal p ope ies o LDPE and HDPE, Eu . Polym. J. 37 (2001) 295-302. 3. Makuuchi, S. 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