Effect of multiple mechanical recycling process on properties of polypropylene

Polimerni materijali prisutni su u svim sferama ljudskoga života. Njihovom upotrebnom nastaju i velike količine polimernog otpada koji je potrebno odgovarajuće zbrinuti kako ne bi predstavljao opasnost za ljude i okoliš. Mehaničko recikliranje pokazalo se kao učinkovit postupak prerade termoplastičnih polimernih materijala kojim je omogućeno njihovo ponovno korištenje u različite svrhe. Iako termoplasti teoretski imaju praktično neograničenu mogućnost višestrukog recikliranja bez gubitka svojstava, zbog nečistoća koje se mogu naći u polimernom materijalu potencijalno ipak može doći do negativnog utjecaja na svojstva. U ovom radu, upravo zbog prethodno navedenog, praćen je utjecaj višestrukih ciklusa mehaničkog recikliranja na svojstva polipropilena (PP). Uzorci čija su se svojstva pratila pripremljeni su miješanjem čistog PP, industrijski recikliranog PP, željezovog(III) oksida te metaliziranog PP dobivenog od ambalažnog otpada. Nakon pripreme smjesa provedena su četiri ciklusa mehaničkog recikliranja ekstudiranjem. U svrhu praćenja utjecaja višestrukih ciklusa mehaničkog recikliranja na svojstva provedena je karakterizacija različitim metodama. Diferencijalnom pretražnom kalorimetrijom (DSC) određene su temperature taljenja (Tm) i kristalizacije (Tc) te toplinski tokovi uslijed endotermnih (ΔHm) i egzotermnih (ΔHc) promjena. Na temelju određenog, izračunat je i stupanj kristalnosti (Xc). Skenirajućim elektronskim mikroskopom praćene su promjene u morfologiji i sastavu ispitivanih uzoraka. Nadalje, određen je maseni protok taljevine (MFR), a na kraju je uslijedilo ispitivanje mehaničkih svojstava uzoraka pomoću mehaničke kidalice. Svojstva su se pratila nakon svakog ciklusa recikliranja. Rezultati istraživanja pokazali su da višestruko mehaničko recikliranje nema značajnog negativnog utjecaja na kemijsku strukturu i svojstva PP koja bi onemogućila njegovu primjenu tj. mehaničko recikliranje pokazalo se kao učinkovita metoda oporabe PP.Polymeric materials are present in all spheres of human life. Their use generates large amounts of polymer waste, which must be properly managed to prevent it from posing a hazard to humans and the environment. Mechanical recycling has proven to be an effective way to process thermoplastic polymer materials, allowing their reuse for various purposes. Although thermoplastics theoretically have a virtually unlimited potential for multiple recycling cycles without loss of properties, impurities that may be present in the polymer material can potentially have a negative impact on properties. In this study, the effect of multiple cycles of mechanical recycling on the properties of polypropylene (PP) was investigated for this very reason. The samples whose properties were studied were prepared by mixing pure PP, industrially recycled PP, iron(III) oxide and metallized PP from packaging waste. After the mixtures were prepared, four cycles of mechanical recycling by extrusion were performed. In order to monitor the effects of multiple cycles of mechanical recycling on the properties, characterization was performed using different methods. Differential scanning calorimetry (DSC) was used to determine the melting temperature (Tm) and crystallization temperature (Tc), as well as the heat flows due to endothermic (ΔHm) and exothermic (ΔHc) changes. The degree of crystallinity (Xc) was also calculated based on the data. Changes in the morphology and composition of the tested samples were observed by scanning electron microscopy. In addition, the melt flow rate (MFR) was determined and finally the mechanical properties of the samples were tested using a universal testing machine. The properties were monitored after each recycling cycle. The research results showed that multiple mechanical recycling cycles did not have significant negative effects on the chemical structure and properties of PP that would hinder its application. Mechanical recycling has been shown to be an effective method for the recovery of PP