ABSTRACT:The gelatinization and extrusion processes of corn starch were studied. Differential scanning calorimetry was used to determine the gelatinization temperature as a function of the water content. Plasticized corn starch was processed in single-and twin-screw extruders to produce thermoplastic materials. The mechanical properties of the films obtained in the twin-screw extruder with the addition of different quantities of water were evaluated. Dynamic mechanical analysis applied to thermoplastic starch samples obtained with 33% (w/w) total plasticizers showed two transitions, attributed to the presence of two phases in the starch-glycerol-water system.

Resumo: Os processos de gelatinização e de extrusão de amido de milho foram estudados. Calorimetria diferencial de varredura e miscroscopia óptica foram utilizadas na determinação da temperatura de gelatinização, T(G), em função do grau de umidade. Misturado a plastificantes, o amido foi processado em extrusoras monoe dupla-rosca para obtenção de termoplásticos. As propriedades mecânicas dos filmes obtidos por processamento em extrusora dupla-rosca foram investigadas. A análise termo-dinâmico-mecânica do filme de amido termoplástico com 33% (p/p) de plastificantes revela a presença de duas transições distintas, atribuídas às transições das duas macromoléculas constituintes do amido. Palavras-chave:Gelatinização, amidos termoplásticos, extrusão, propriedades físicas. Investigation of corn starch gelatinization and extrusion processesAbstract: The gelatinization and extrusion processes of corn starch were studied. Differential scanning calorimetry and optical microscopy were used to determine the gelatinization temperature, as a function of the water content. Plasticized corn starch was processed in single-and twin-screw extruders to produce thermoplastic materials. The mechanical properties of the films obtained in the twin-screw extruder were evaluated. The thermo-dynamical-mechanical analysis of the thermoplastic starch with 33% (w/w) plasticizers showed two transitions, attributed to the starch constituents.Keywords: Gelatinization, thermoplastic starch, extrusion, physical properties. IntroduçãoOs artefatos plásticos convencionais produzidos a partir de polímeros sintéticos são inertes ao ataque imediato de microorganismos. Embora esta propriedade faça com que esses materiais apresentem um tempo longo de vida útil, por outro lado, ocasionam sérios problemas ambientais após o seu descarte, devido ao grande tempo necessário para a sua degradação [1,2] . A adição de um substrato biodegradável a uma matriz polimérica sintética induz a digestão de tal aditivo por microorganismos, o que favorece o esfarelamento da matriz polimérica sintética [3] . A introdução de amido a matrizes poliméricas sintéti-cas, realizada inicialmente em meados dos anos 70, tem-se mostrado uma alternativa viável para a obtenção de plásticos mais facilmente biodegradáveis [4] .Atualmente, há o interesse no desenvolvimento de materiais termoplásticos compostos essencialmente de amido [5,6] . O conhecimento de algumas propriedades características do amido e de seu comportamento durante o processamento têm-se mostrado de muita importância para o desenvolvimento de amidos termoplásticos [7][8][9][10] . Ao contrário dos polímeros sintéticos, o amido é obtido a partir de fontes renováveis, sendo biossintetizado e estocado pelas plantas na forma de grânulos de tamanhos variáveis, que dependem da fonte [4] . O amido é constituído de duas macromoléculas principais: a amilopectina, que é uma molécula ramificada, e a amilose, que é uma molécu-la essencialmente linear. Ambas possuem massa molar elevada [11][12][13] .Os grânulos de amido apresentam birr...

Viscosity measurements were carried out on corn starch (CS) and CSsodium alginate (SA) suspensions at low levels of SA [1 to 10% (w/w)], as a function of temperature. The addition of SA caused the granular CS gelatinization process to occur at a lower onset temperature. CS and CS-SA mixtures were extruded in single-and twin-screw extruders, with 15% glycerol and different water contents. Processing of plasticized CS-SA mixtures required lower temperatures, which is consistent with the viscosity results. Homogeneous and flexible extrudates were obtained by processing in a twin-screw extruder. Samples in the composition range between 0 and 10% (w/w) SA were examined using tensile tests as a function of water content. Mechanical properties were dependent on the water content and on the SA composition. A significant increase in the Young's modulus value was observed for the blend containing 1% SA. Dynamic mechanical analysis was carried out for CS and CS-SA blends. Two transitions were detected in the temperature range -80 to 150°C. Scanning electron microscopy was used to examine the morphology of the extruded samples. The surfaces of the films were homogeneous, which demonstrated that the CS granules in all samples were characteristically destructured under the conditions used in processing.

Summary: Novel maleated starches (MSt) were prepared by chemical modification of cornstarch with maleic anhydride (MA), using an internal mixer as a reactor. Benzoyl peroxide (BPO) was chosen as initiator. Physico‐chemical parameters were given by the process, recorded at different MA contents, under the same reaction conditions. Processing was carried out at 50 °C, 30 rpm for 8 min. Torque developed during processing was given by the digital display of the rheometer, and the total specific mechanical energy (SME) input was estimated. FTIR measurements confirmed the successful incorporation of MA into the starch backbone. X‐ray diffractograms obtained for the products revealed disruption of the crystalline structure of native starch. The results indicated that the MA content had a significant effect on the characteristics of the resulting modified starches.