**3.3 Biodegradable polymers**

Due to increasing environmental awareness and the environmental legislations, scientists around the world have made strong efforts to develop methods using natural polymers as an alternative to the petroleum synthetic polymers for industrial and consumer applications. (Liu et al., 2009).

Biodegradable polymers represent a promising solution to the environmental problem of plastic waste disposal. Among the candidate polymers, starch, a low-cost natural polymer, can be processed as a thermoplastic (Rosa et al., 2008).

Starch is being researched both for the production of biodegradable packagings with the use of extrusion blow molding machine, where bags are made even for the formation of edible films to coat industrialized foods or fruits.

The shelf-life of foods is governed by their numerous interactions with their surroundings and can be extended by using protective films. The deterioration of packaged foodstuffs largely depends on the transfers that may occur between the internal environment of the packaged food and the external environment. Edible films can be used to reduce water vapor, oxygen, lipid, and flavor migration between components of multicomponent food products, and between food and the surroundings. Many proteins and polysaccharides have good filmforming properties and can be used in the preparation of edible films (Torres, 1994).

For packagings, which will be used for food transporting, such as bags and boxes, plasticized starches that are commonly called thermoplastic starches (TPS) are used (Stepto, 2003 ).

TPS can be processed through traditional processing conditions (extrusion, blow molding and injection molding increase the properties of the blends and the content of TPS in TPS/PE blends (Rodriguez-Gonzalez et al., 2003).

Carvalho et al. (2005) used carboxylic acids to decrease the viscosity of TPS by controlling the macromolecules of starch. After melt processing in the presence of glycerol, water and carboxylic acids, both the molar masses and viscosity of TPS are decreased. In their previous work (Yu, Wang & Ma, 2005) citric acid (CA) is also used as an additive to modify TPS during melt processing. CA can effectively restrain starch re-crystallization, except for increasing the fluidity of TPS. But the mechanical properties of TPS are decreased, especially the tensile strength (below 4 MPa).

Chaudhary et al. (2008) obtained thermoplastic resin with a mixture of different concentrations of unmodified starches with 0%, 28%, 50% and 80% amylose; 80% amylose hydroxypropylated starch using extrusion process with several variations of screw speed, die pressure, motor torque, mean residence time and specific mechanical energy.

Pea starch-based composites reinforced with citric acid-modified pea starch (CAPS) and citric acid-modified rice starch (CARS), respectively, were prepared through screw extrusion to obtain biodegradable polysaccharide (CA-modified granular starch/TPS) composites to be used with a potential replacement for edible films, food packaging, biodegradable packaging, etc. The CARS/TPS composites exhibited better storage modulus, tensile strength, elongation at break and water vapor barrier than CAPS/TPS composites because of the smaller size of granular CARS (Ma et al., 2009).

Due to increasing environmental awareness and the environmental legislations, scientists around the world have made strong efforts to develop methods using natural polymers as an alternative to the petroleum synthetic polymers for industrial and consumer applications.

Biodegradable polymers represent a promising solution to the environmental problem of plastic waste disposal. Among the candidate polymers, starch, a low-cost natural polymer,

Starch is being researched both for the production of biodegradable packagings with the use of extrusion blow molding machine, where bags are made even for the formation of edible

The shelf-life of foods is governed by their numerous interactions with their surroundings and can be extended by using protective films. The deterioration of packaged foodstuffs largely depends on the transfers that may occur between the internal environment of the packaged food and the external environment. Edible films can be used to reduce water vapor, oxygen, lipid, and flavor migration between components of multicomponent food products, and between food and the surroundings. Many proteins and polysaccharides have good film-

For packagings, which will be used for food transporting, such as bags and boxes, plasticized starches that are commonly called thermoplastic starches (TPS) are used (Stepto,

TPS can be processed through traditional processing conditions (extrusion, blow molding and injection molding increase the properties of the blends and the content of TPS in

Carvalho et al. (2005) used carboxylic acids to decrease the viscosity of TPS by controlling the macromolecules of starch. After melt processing in the presence of glycerol, water and carboxylic acids, both the molar masses and viscosity of TPS are decreased. In their previous work (Yu, Wang & Ma, 2005) citric acid (CA) is also used as an additive to modify TPS during melt processing. CA can effectively restrain starch re-crystallization, except for increasing the fluidity of TPS. But the mechanical properties of TPS are decreased, especially

Chaudhary et al. (2008) obtained thermoplastic resin with a mixture of different concentrations of unmodified starches with 0%, 28%, 50% and 80% amylose; 80% amylose hydroxypropylated starch using extrusion process with several variations of screw speed,

Pea starch-based composites reinforced with citric acid-modified pea starch (CAPS) and citric acid-modified rice starch (CARS), respectively, were prepared through screw extrusion to obtain biodegradable polysaccharide (CA-modified granular starch/TPS) composites to be used with a potential replacement for edible films, food packaging, biodegradable packaging, etc. The CARS/TPS composites exhibited better storage modulus, tensile strength, elongation at break and water vapor barrier than CAPS/TPS composites because

die pressure, motor torque, mean residence time and specific mechanical energy.

forming properties and can be used in the preparation of edible films (Torres, 1994).

**3.3 Biodegradable polymers** 

can be processed as a thermoplastic (Rosa et al., 2008).

films to coat industrialized foods or fruits.

TPS/PE blends (Rodriguez-Gonzalez et al., 2003).

of the smaller size of granular CARS (Ma et al., 2009).

the tensile strength (below 4 MPa).

(Liu et al., 2009).

2003 ).

Flores et al. (2010) used a mixture of experimental design to study the physical and microbiological properties of tapioca starch-based glycerol edible films with the addition of xanthan gum (XG) and potassium sorbate (PS) and obtained through extrusion technology. The results showed that PS presence decreased the ultimate tensile strength and elastic modulus and increased strain at break. XG produced a reinforcing effect on the films and also enhanced solubility in water and decreased moisture content.

Guan & Hanna (2006) have extruded biodegradable composite foams based on starch acetate and poly (tetraethylene adipate-co-terephthalate) (EBC). It was reported that low EBC contents in the blends favored the miscibility of the two polymers, as characterized by an increase of the glass transition temperature of starch acetate, a decrease in the melting point temperature of starch and EBC in a differential scanning calorimetry (SEM) analysis and the formation of a homogeneous morphology observed with SEM. Large amounts of EBC decreased the miscibility of these two polymers.

Multifunctional epoxy-based copolymers can be used as chain-extender (CE) to increase the molecular weight and create branching in polylactides (PLA). Li & Huneault (2011) studied the effect of a multifunctional epoxy-acrylic-styrene copolymer on the properties of PLA/Thermoplastic Starch (PLA/TPS) blends that were prepared by twin-screw extrusion. The plasticizers were mixed together in the first half of the extruder to complete starch gelatinization. Water was removed by devolatilization at midex-truder and the PLA matrix was mixed with the water-free TPS in the latter portion of the compounding process. The standard blends comprised 27% TPS in the PLA matrix. The TPS phase itself comprised 36% plasticizer in the form of glycerol or sorbitol. The blends were injection molded into standard test bars and their tensile properties were measured. It was found that the combination of interfacial modification and chain-extension strategies led to greatly improved ductility. The viscosity of the PLA/TPS blends was also dramatically increased by adding a small amount of epoxy-based chain extender. This is of great interest for polymer processing techniques (such as foaming or film blowing) that require high melt strength.

Nabar et al. (2006) produced the cylindrical starch foam shapes on a small scale (∼11-12 kg/hr) Werner Pfleiderer ZSK-30 twin-screw extrusion (TSE) process using water, which functions as a plasticizer as well as a blowing agent. The properties of the starch foams depend on the type of starch used (hydroxypropylated high amylose corn starch, 70% amylose), the amount of water and additives (poly(hydroxyamino ether)) (PHAE) used, and extrusion conditions such as temperature and the screw configuration.


Table 3 summarizes some other works with biopolymers using starch as base.

Physical and/or Chemical Modifications of Starch by Thermoplastic Extrusion 51

The thermoplastic extrusion process is capable of causing changes in starch, making it present a large variety of applications both in the food industry and in other industries; and, as a matter of fact, the use of starches in packagings has increased due to the easy process in

Abu-Hardan, M.; Hill, S.E. & Farhat, I. ( 2011). Starch conversion and expansion behaviour

Alves, R.M.L.; Grossmann, M.V.E. & Silva, R.S.S.F. (1999). Gelling properties of extruded

Bello-Pérez, L.A.; González-Soto, R.A. ; Sánchez-Rivero, M.M. ; Gutiérrez-Meraz, F. &

Brandelero, R. P. H.; Yamashita, F.; Grossmann, M.V.E. (2010). The effect of surfactant

Carvalho, A. J. F.; Zambon, M. D.; da Silva Curvelo, A. A. & Gandini, A. (2005).

Céspedes, M.A.L. ; Martínez-Bustos, F. & Chang, Y.K. (2010). The effect of extruded orange

Chang, Y. & Lii, C. (1992).Preparation of starch phosphates by extrusion. *Journal of Food* 

Chang, Y. K. (1989). *Efeito da concentração de ácido, umidade e temperatura na hidrólise de amido* 

Charboniere, R.; Duprat, F. & Guilbot, A. (1973).Change in various starch by cooking-

Chaudhary, A.L.; Miler, M.; Torley, P.J.; Sopade, P.A. & Halley, P.J. (2008). Amylose content

Chaunier, L.; Valle, G. D.; & Lourdin, D. (2007). Relationships between texture, mechanical properties and structure of cornflakes. *Food Research International*, Vol. 40, 493–503. Chiang, B-Y. & Johnson, J.A. (1977). Gelatinization of starch in extruded products. *Cereal* 

Cho, K.Y. & Rizvi, S.S.H. (2010). New generation of healthy snack food by supercritical fluid extrusion. *Journal of Food Processing and Preservation*, Vol. 34, No.2, 192-218.

of wheat starch cooked with either; palm, soybean or sunflower oils in a co-rotating intermeshing twin-screw extruder. *International Journal of Food Science and* 

Vargas-Torres, A. ( 2006). Extrusion of starches from non-conventional sources for

Tween 80 on the hydrophilicity, water vapor permeation, and the mechanical properties of cassava starch and poly (butylenes adipatecoterephthalate) (PBAT)

Thermoplastic starch modification during melt processing: Hydrolysis catalyzed by

pulp on enzymatic hydrolysis of starch and glucose retardation index . *Food and* 

*de mandioca por extrusão termoplástica, visando a produção de álcool*. Tese de

extrusion processing, part II, physical structure of extruded products. *Cereal Science* 

and chemical modification effects on the extrusion of thermoplastic starch from

modifying and promoting interactions between starch and other polymers.

yam (*Dioscorea alata*) starch. *Food Chemistry*, Vol. 67, 123-127.

resistant starch production *Agrociencia*, Vol. 40, No. 4, 441-448.

blend films. *Carbohydrate Polymers*, Vol. 82, 1102–1109.

carboxylic acids. *Carbohydrate Polymers*, Vol. *62*, 387–390.

*Bioprocess Technology*, Vol. 3, No.5, 684-692.

maize. *Carbohydrate Polymers*, Vol. 74, 907–913.

*Science,* Vol. 57, No.1, 203-5.

Doutorado, FEA, UNICAMP.

*Chemistry*, Vol.54, No.3, 436-443.

*Today*, Vol.18, No.9, 286.

*Technology*, Vol. 46, No.2, 268-274.

**4. Conclusion** 

**5. References** 


Table 3. Biodegradable polimers obtained with thermoplastic extrusion
