Preparation and characterization of polyethylene/thermoplastic starch blends

Danas se kao ambalažni materijali uglavnom koriste sintetski polimerni materijali dobiveni iz nafte. Masovno iskorištavanje nafnih sirovina uzrokuje globalne klimatske promjene i osim toga, njihove raspoložive količine su ograničene, a dobiveni sintetski polimerni materijali nerazgradivi zbog čega dolazi do gomilanja ambalažne „plastike“ u okolišu. Iz tih je razloga tema brojnih znanstvenih radova razvoj biorazgradivih polimernih materijala iz obnovljivih izvora. Njihova primjena je, u odnosu na sintetske polimerne materijale, ograničena zbog lošijih svojstava i otežane prerade. Da bi se smanjila primjena sintetskih polimernih materijala, a u isto vrijeme zadržala kvaliteta i niska cijena ambalaže, kao dobro rješenje nameće se miješanje sintetskih i biorazgradivih polimera. Biorazgradivi polimerni materijal pripremljen i karakteriziran u ovom radu dobiven je miješanjem polietilena niske gustoće (PE-LD) i plastificiranog pšeničnog škroba, tj. termoplastičnog škroba (TPS). TPS je plastificiran s 40 mas. % glicerola u jednopužnom ekstruderu, a u Brabender gnjetilici priređene su mješavine PE-LD/TPS sa masenim udjelom TPS-a u rasponu od 10 mas. % do 50 mas. %. Toplinska svojstva dobivenih mješavina određena su tehnikom diferencijalne pretražne kalorimetrije (DSC) i termogravimetrijske analize (TGA). Struktura TPS-a i prirodnog škroba uspoređena je kombiniranom tehnikom infracrvene spektroskopije s Fourierovim transformacijama i prigušene totalne refleksije, FTIR-ATR spektroskopijom. Mehanička svojstva mješavina određena su rasteznim ispitivanjem, a barijerna svojstva mjerenjem debljine njihova filma, propusnosti vodene pare, te apsorpcije vode. Miješanje TPS-a sa PE-LD-om rezultiralo je puno boljim toplinskim, mehaničkim i barijernim svojstvima, odnosno primjenskim svojstvima u odnosu na čisti TPS. Obratno, dodatkom TPS-a u PE-LD matricu narušavaju se mehanička svojstva PE-LD-a ali dobivene PE-LD/TPS mješavine imaju prihvatljiva svojstva, unutar granica primjene, što ukazuje na mogućnost daljnjeg razvoja i poboljšanja analiziranih mješavina. Također, ugradnja TPS-a u PE-LD matricu potiče biorazgradnju PE-LD/TPS mješavina pa je na taj način moguće dobiti visoko funkcionalni ambalažni materijal koji bi pridonio očuvanju okoliša i ljudskog zdravlja.Synthetic polymers, gotten from crude oil, are the most commonly used packaging materials today. A development of biomaterials from renewable sources has gained considerable momentum in recent times due to global climate change issues linked to mass-scale exploitation of petroleum-based feedstock whose volumes are limited. Synthetic polymer materials are non-biodegradable so there is also problem of accumulation of polymer packaging waste in the environment. The use of biodegradable polymers compared to synthetic polymeric materials is restricted due to their inferior properties and difficult way of processing. In order to reduce the amount of application of synthetic polymers, and maintain the quality and low cost packaging, blending synthetic and biodegradable polymers present itself as a good solution. In this study we have prepared biodegradable polymeric materials, by mixing low density polyethylene (LDPE) and plasticized wheat starch, i.e. thermoplastic starch (TPS), and characterised it with a number of techniques. TPS is prepared by coating with wheat starch 40 wt. % glycerol in single screw extruders. LDPE/TPS blends varied from 10% to 50 wt. % by weight of TPS were prepared in a Brabender mixer. The thermal properties of the composites are determined by the technique of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The structure of TPS and natural starch was compared by combined infrared spectroscopy technique with Fourier transforms and attenuated total reflection, FTIR-ATR spectroscopy. The mechanical properties of the composites are determined by tensile test and barrier properties by measuring the thickness of their film, water vapor permeability and water absorption. Mixing of TPS with LDPE has resulted in much better thermal, mechanical and barrier properties, i.e. application properties compared to TPS. Conversely, the mechanical properties of LDPE are disrupted by adding TPS to the LDPE matrix, but the LDPE/TPS blends have acceptable properties within the limits of application, indicating the possibility of further development and improvement of the analyzed blends. Also, incorporating TPS into a LDPE matrix encourages the biodegradation of LDPE/TPS blends, so it is possible to obtain high functional packaging material that would contribute to the preservation of the environment and human health