Extrudates of Cornstarch with Urea and Glycols: Structure/Mechanical Property Relations

ABSTRACT:The structural and mechanical properties of compression-molded normal and high-amylose maize starches were studied as a function of processing water content and ageing time. Rubbery thermoplastic starches were produced by compression molding of four maize starches with differences in amylose content and amylopectin structure. Glycerol (30% on the basis of dry starch) and water (between 10 and 35% on the basis of total mass) were used as plasticizers. After processing, the amorphous thermoplastic starch materials crystallized during ageing. The semicrystalline materials contained both E-type and V-type, as well as B-type crystallinity. The properties of the thermoplastic starch materials are dependent on water content during processing, starch source, and ageing time. The normal maize starch materials are highly flexible with elongations between 56 and 104%. The elongations of the high-amylose maize starch materials were between 5-35%. The tensile stress and E-modulus of the normal maize starch materials were in the range of 3.9-6.7 and 27-131 MPa, respectively. The tensile stress and E-modulus of the high-amylose maize starch materials increased from approximately 0.5 to 23 and 5 to 700 MPa, respectively, with increasing water content during processing from 10 to 35%. The differences in mechanical properties of the normal and high-amylose materials were explained by differences in the structure of the amylose and amylopectin structure. It was concluded that both lead to differences in the starch network.

Section: Methodsmentioning

confidence: 99%

Structure and properties of compression-molded thermoplastic starch materials from normal and high-amylose maize starches

Soest

Borger

1997

“…The is sometimes mentioned in the literature 15 but ducted exactly 48 h after their preparation. However, as the casting method is not reproducible, calorimetric measurement procedure was similar the glycerol contents of films specially prepared for all samples regardless of composition.…”

Section: Introductionmentioning

confidence: 99%

?Antiplasticization? in starch-glycerol films?

Lourdin¹,

Bizot²,

Colonna³

1997

315

Calorimetric, mechanical, and thermomechanical properties have been measured on starch films with various glycerol/water contents. For calorimetric measurements, a continuous decrease in T g was observed as glycerol increases from 0 to 25%. Mechanical properties exhibit a minimum of elongation at break for glycerol content Ç 12%. In slightly hydrated starch films not containing another plasticizer, a b relaxation is detected by DMTA around 068ЊC. This relaxation is modified by the presence of glycerol, the a relaxation of which appears in the same temperature range. Results are discussed comparing with the well-known antiplasticization effect in synthetic polymers such as PVC and PC. The combination of the plasticizer a mode and the polymer b mode is considered.

“…But even in this case, the mechanical properties of the materials produced are very poor (especially in tensile strength), depending on the kind of plasticizer used. 7 Glycerol is the most effective plasticizer but still cannot prevent the degradation of starch macromolecules during plasticization. It was found that the decomposition depends on the amount of glycerol as well as on the temperature used.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, characterization, and biodegradability of fatty-acid esters of amylose and starch

Aburto

Alric

Thiebaud

et al. 1999

162

A series of starch and amylose esters with different degrees of substitution and side-chain length were prepared and studied. The esters were prepared by acylation of the polysaccharide with the appropriate acid chlorides, such as octanoic, dodecanoic, and octadecanoic. The degrees of substitution were 0.54, 1.8, and 2.7. After preparation, the resulting esters were characterized by elemental analysis, 1 H nuclear magnetic resonance ( 1 H-NMR), Fourier transform infrared (FTIR), differential scanning (DSC), thermogravimetric analysis (TGA), contact angle, and water uptake measurements. Their mechanical properties and, in particular, the tensile strength and elongation at break depend on the side-chain length and on the degree of substitution. The extent of their biodegradability, after exposure to activated sludge, was assessed by weight loss measurements and scanning electron microscopy (SEM). It was found that these new materials are biodegradable, and the biodegradation rate decreases with increasing degree of esterification.