The effect of accelerated aging on the mechanical properties of PMMA denture base materials modified with itaconates

Abstract

This study evaluated the effect of accelerated aging on tensile strength, elongation at break, hardness and Charpy impact strength in commercial PMMA denture base material modified with di-methyl itaconate (DMI) and di-n-butyl itaconate (DBI). The samples were prepared by modifying commercial formulation by addition of itaconates in the amounts of 2.5, 5, 7.5 and 10 % by weight. After polymerization samples were characterized by FT-IR and DSC analysis while residual monomer content was determined by HPLC-UV. Accelerated ageing was performed at 70°C in water for periods of 7, 15 and 30 days. Tensile measurements were performed using an Instron testing machine while the hardness of the polymerized samples was measured by the Shore D method. The addition of itaconate significantly reduces the residual MMA. Even at the small amounts of added itaconates (2.5%) the residual MMA content was reduced by 50%. The increase of itaconate content in the system leads to the decrease of residual MMA. It has been found that the addition of di-n-alkyl itaconates decreases the tensile strength, hardness and Charpy impact strength and increases elongation at break. Samples modified with DMI had higher values of tensile strength, hardness and Charpy impact strength compared to the ones modified with DBI. This is explained by the fact that DBI has longer side chain compared to DMI. After accelerated aging during a 30 days period the tensile strength decreased for all the investigated samples. The addition of DMI had no effect on the material aging and the values for the tensile strength of all of the investigated samples decreased around 20%, while for the samples modified with DBI, the increase of the amount of DBI in the polymerized material leads to the higher decrease of the tensile strength after the complete accelerated aging period of 30 days, although after the first seven days of the accelerated aging the values of hardness have increased for all of the investigated samples. Such behavior is explained as a result of the polymer chain relaxation. The values of Charpy impact strength decreased after accelerated aging. The amount of added DMI had no affect on the decrease of Charpy impact strength after accelerated aging, the decrease was similar as for pure PMMA. The decrease of Charpy impact strength increased with increase of the amount of added DBI.

Itakonati, estri itakonske kiseline, zbog svoje niske toksičnosti i mogućnosti da se dobiju iz nepetrohemijskih izvora veoma su pogodni materijali za biomedicinsku primenu. Zbog svoje strukturne sličnosti sa metakrilatima oni predstavljaju najvažniji materijal za zamenu metakrilatnih polimera. U ovom radu su sintetisani novi dentalni materijali tako što je komercijalni dentalni materijal modifikovan di-n-metil-itakonatom (DMI) (PMMA/PDMI) ili di-n-butil-itakonatom (DBI) (PMMA/PDBI), a dobijeni proizvodi okarakterisani su infracrvenom spektroskopijom (FT-IR), tečnom hromatografijom (HPLC-UV) i diferencijalnom skenirajućom kalorimetrijom (DSC). Pod istim eksperimentalnim uslovima sintetisan je i referentni uzorak poli(metil-metakrilata) (PMMA). Glavni cilj rada je bio da se ispita kako uvođenje male količine itakonata u smešu za polimerizovanje metal metakrilata (MMA) utiče na mehanička svojstva ovako dobijenih dentalnih materijala i to u dužem vremenskom periodu. Zato je ispitan uticaj ubrzanog starenja na mehanička svojstva sintetisanih materijala. Ubrzano starenje je izvedeno u destilovanoj vodi na temperaturi od 70°C u trajanju od 30 dana. Uzorcima su ispitana mehanička svojstva - zatezna čvrstoća, relativna deformacija pri kidanju, tvrdoća i žilavost. Rezultati su pokazali da sa porastom udela DMI i DBI u materijalu ispitivani parametri opadaju kako pre tako i nakon starenja, što je izraženije kod uzoraka PMMA/PDBI. Receptura za bazu zubnih proteza modifikovana sa 2,5 mas% DMI-a pokazala je najbolje rezultate. Ova receptura ima za 50% manju količinu zaostalog MMA u odnosu na referentni uzorak (komercijalni PMMA materijal za bazu proteze), a istovremeno poseduje slične vrednosti zatezne čvrstoće, relativne deformacije pri kidanju i žilavosti, i povećanu tvrdoću u odnosu na referentni uzorak.