Biodegradable and functionally superior starch–polyester nanocomposites from reactive extrusion

Abstract

Biodegradable starch-polyester polymer composites are useful in many applications ranging from numerous packaging end-uses to tissue engineering. However the amount of starch that can form composites with polyesters without significant property deterioration is typically less than 25% because of thermodynamic immiscibility between the two polymers. We have developed a reactive extrusion process in which high amounts of starch (approx. 40 wt%) can be blended with a biodegradable polyester (polycaprolactone, PCL) resulting in tough nanocomposite blends with elongational properties approaching that of 100% PCL. We hypothesize that starch was oxidized and then crosslinked with PCL in the presence of an oxidizing/ crosslinking agent and modified montmorillonite (MMT) organoclay, thus compatibilizing the two polymers. Starch, PCL, plasticizer, MMT organoclay, oxidizing/crosslinking agent and catalysts were extruded in a co-rotating twinscrew extruder and injection molded at 120°C. Elongational properties of reactively extruded starch-PCL nanocomposite blends approached that of 100% PCL at 3 and 6 wt% organoclay. Strength and modulus remained the same as starch-PCL composites prepared from simple physical mixing without any crosslinking. X-ray diffraction results showed mainly intercalated flocculated behavior of clay at 1,3,6, and 9wt% organoclay. Scanning electron microscopy (SEM) showed that there was improved starch-PCL interfacial adhesion in reactively extruded blends with crosslinking than in starch-PCL composites without crosslinking. Dynamic mechanical analysis showed changes in primary ␣-transition temperatures for both the starch and PCL fractions, reflecting crosslinking changes in the nanocomposite blends at different organoclay contents. Also starch-polytetramethylene adipate-co-terephthalate (PAT) blends prepared by the above reactive extrusion process showed the same trend of elongational properties approaching that of 100% PAT. The reactive extrusion concept can be extended to other starch-PCL like polymer blends with polymers like polyvinyl alcohol on one side and polybutylene succinate, polyhydroxy butyrate-valerate and polylactic acid on the other to create cheap, novel and compatible biodegradable polymer blends with increased toughness.

Bionanocomposites: A New Concept of Ecological, Bioinspired, and Functional Hybrid Materials

“…[19][20][21] Neutral polysaccharides, such as starch derived from corn, wheat, rice or potato, and cellulose and its derivatives, are the main biopolymers employed in the development of green nanocomposites. [23][24][25][32][33][34] These materials generally incorporate natural or synthetic clay minerals as inorganic nanofillers as well as organically modified clay minerals, giving intercalation or exfoliation compounds. Montmorillonite and cloisite are the usual silicates used in these studies, acting as nanocharges that can produce a reinforcing effect in the biopolymer matrix, thereby resulting in improved mechanical properties.…”

An Introduction to Bio‐nanohybrid Materials

“…Organoclays show a better affinity towards non-polar species, which in this way may be assembled to the internal and the external surfaces of the modified clay mineral. Various authors have reported the preparation of bio-nanohybrid materials based on organoclays [137][138][139][140][141][142][143][144]. As this topic is specifically treated in Chapter 8, we will refer to it briefly here with some examples.…”

A high-resolution solid-state NMR study on starch–clay nanocomposites and the effect of aging on clay dispersion

“…[1][2][3] Thermoplastic starch has been produced using conventional thermal extrusion methods at suitable temperatures using added plasticizers (usually water and glycerol), and, in many cases, other polymer additives to modify the properties of starch-based materials. [4][5][6][7][8][9][10][11][12][13] Polymer-clay nanocomposites have attracted a great deal of interest by researchers in academia and industry, because significant improvements in many aspects of material performance can be obtained when using a very low dosing amount of such layered nanoparticles. [14][15][16][17][18][19] The property improvements of these doped materials compared with pure polymers or conventional micro-or macrocomposites are due to the significantly strengthened interfacial interactions between polymer chains and nanoparticles (layer thickness of the order of 1 nm, diameter of 30-1000 nm) when these particles are well dispersed in the polymer matrix.…”