Starch

 Encyclopedia of Polymer Polymer Sceince and Technology c 2005 John Wiley & Sons, Inc. All rights reserved. Copyright 

STARCH Introduction In nature, starch represents a link with the energy of the sun, which is partially captured during photosynthesis. Starch serves as a food reserve for plants and provides a mechanism by which nonphotosynthesizing organisms, such as man, can utilize the energy supplied by the sun. Today, starch is inexpensive and is available annually from corn and other crops, and is produced in excess of current market needs in the United States and Europe (1). Starch is totally biodegradable in a wide variety of environments and could could permit permit the develo developme pment nt of totall totally y degrad degradabl able e produc products ts for specifi specificc market market demands. Degradation or incineration of starch products would recycle atmospheric CO2  trapped by starch-producing plants and would not increase potential global warming (2) (see also E NVIRONMENTALLY  D  D EGRADABLE P LASTICS). For these reasons there has been renewed interest in starch-based plastics in recent years. Earlier studies of starch esters and ethers (3–10) indicated that they had inadequate properties in comparison with cellulose derivatives for most applications. More recently, starch graft copolymers (2), starch plastic composites (11,12), and starch itself (13–17) have been proposed as plastic materials. Starch consists of two major components: amylose, a mostly linear  α -D(1-4)glucan and amylopectin, an α -D-(1-4)-glucan which has α -D(16) linkages at the branch point. The linear amylose molecules of starch have a molecular weight of 0.2–2 million, whereas the branched amylopectin molecules have molecular OLYSACCHARIDES AND C ARBOHY weights as high as 100–400 million (18,19) (see P OLYSACCHARIDES DRATE  P OLYMERS). In nature, starch is found as crystalline beads of about 15–100 µm in diameter, in three crystalline modifications designated A (cereal), B (tuber), and C (smooth pea and various beans), all characterized by double helices: almost perfect left-handed, six-fold structures, as elucidated by X-ray diffraction experiments (18,20,21). Starch beads may also show V crystallinity, characterized by a single helix when starch is in presence of fatty acids (22). Crys Crysta talli lline ne star starch ch bead beadss in plas plasti tics cs can can be used used as Fill Filler erss (qv) (qv) or can can be tran transsformed into thermoplastic starch, which can be processed alone or in combination with specific synthetic polymers. To make starch thermoplastic, its crystalline structure structure has to be destroyed destroyed by pressure, pressure, heat, mechanical mechanical work, work, and Plasticizers (qv) such as water, glycerol, or other polyols. This article reviews the main results obtained in the fields of starch-filled plastics and thermoplastic starch, with particular attention to the concepts of  gelatiniza gelatinization, tion, destructur destructurizati ization, on, extrusion extrusion cooking, cooking, and the complexati complexation on of  1

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amylose by means of polymeric complexing agents with the formation of specifi cific supramolecular structures. The behaviors of products now in the market are considered in terms of processability, physical-chemical and physical-mechanical properties, and biodegradation rates.

Starch-Filled Plastics Starch can be used as a natural filler in traditional plastics (11,23– (11,23 –33) and particularly in polyolefi polyolefins. When blended with starch beads, polyethylene  films  fi lms (34) biodeteriorate on exposure to a soil environment. The microbial consumption of  the starch component, in fact, leads to increased porosity, void formation, and the loss of integrity of the plastic matrix. Generally (32,35 –38), starch is added at fairly low concentrations (6– (6 –15%); the overall disintegration of these materials is achieved by the use of transition-metal compounds, soluble in the thermoplastic matrix, as pro-oxidant additives which catalyze the photo- and thermooxidative process (39– (39–44). Starch-fi Starch-filled polyethylenes containing pro-oxidants are commonly used in agricultur agricultural al mulch mulch film, in bags, bags, and in six-pac six-pack k yoke yoke packag packaging ing.. Commer Commercia ciall prodprod fi rst by Ecostar and Archer Daniels ucts based on this technology have been sold  first Midland Cos. (45,46). In the St. Lawrence Starch (47,48) technology, bought by Ecostar, regular corn starch was treated with a Silane Coupling Agents (qv) to make it compatible with hydrophobic polymers, and dried to less than 1% of water content. It was then mixed with the other additives such as an unsaturated fat or fatty acid autoxidant to form a master batch, which is added to a commodity polymer. The polymer can then be processed by convenient methods, including  film blowing, Injection Molding (qv) and Blow Molding (qv). The temperature had to be kept below 230 ◦ C to prevent decomposition of  the starch, and exposure of the master batch to air had to be minimized to avoid water absorption. Direct addition of starch and autoxidant without the master batch step can also be used; as this requires some specifi speci fic equipment, it is only prac practi tica call for for larg large e volu volume mess (42) (42).. It was clai claime med d that that unde underr appr approp opri riat ate e cond condit itio ions ns,, the disintegration time of a buried carrier bag, containing an Ecostar additive to reach 6% starch, will be reduced from hundreds of years to 3 –6 years (38). However there is no evidence of a compliance of such materials with the norms of biodegradability and compostability already in place at the international level. Moreover, the destabilization of polyethylene induced by the pro-oxidants may signifi significantly affect its in-use performance as a function of time. Within the fi the  field eld of starch-fi starch-filled materials other systems were studied, some of which were completely biodegradable, such as starch/poly( ε-caprolactone) (49), and others others partia partially lly biodeg biodegrad radabl able, e, such such as starch starch/PV /PVC/p C/poly oly ( ε-caprolactone) and its deriva derivativ tives es (50) (50) or starch starch/mo /modi difi fied polyes polyester terss (51). (51). ln all these these cases cases starch granules are used to increase the surface area available for attack by microorganisms.

Thermoplastic Starch Starc Starch h can be gelati gelatiniz nized ed by extrus extrusion ion cookin cooking g techno technolog logy y (52– (52–66). 66). As desc descri ribe bed d by Conw Conway ay in 1971 1971,, extr extrus usio ion n cook cookin ing g and and form formin ing g is char charac acte teri rize zed d by suf  suf ficient cient work work

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and heat being applied to a cereal-based product to cook or gelatinize completely all the ingredients. In general the main components of high pressure cooking extruders are feeders, compression screws, barrels, dies, and heating systems (52). The effects of processing conditions on the gelatinization of starch and on the texture of the extruded product have been studied by several researchers (53 –70). Gelatinized materials with different starch viscosity, water solubility, and water absorption have been prepared by altering the moisture content of the raw product and the temperature or the pressure in the extruder. It has been demonstrated that an extrusion-cooked starch can be solubilized without any formation of maltodextrins, and that the extent of solubilization depends on extrusion temperature, moisture content of the starch before extrusion, and the amylose/amylopectin ratio. Mercier (69) analyzed the properties of different types of starch and considered the influence of the following parameters: moisture content between 10.5 and 28%, barrel temperature between 70 and 250 ◦ C, residence time between 20 s and 2 min, in a twin-screw extruder. Corn starch, after extrusion cooking, gave a solubility lower than 35%, whereas potato starch solubility was up to 80% (Fig. 1). Starch gelatinization   is a dif ficult term to clearly define and it was used in the past to describe loss of crystallinity of starch granules, notwithstanding  the process conditions applied (18), namely, extrusion cooking, spray drying, or heating of diluted starch slurries. The work carried out by Donovan in 1979 (71) and by Colonna and Mercier in 1985 (72) gave, however, a clear explanation of two different conditions for the loss of crystallinity of starch. Colonna reported that all starches exhibit a pure gelatinization phenomenon, which is the disorganization of  the semicrystalline structure of the starch granules during heating in the presence of a water fraction >0.9. For normal genotypes, gelatinization occurs in two stages. The first step, at around 60–70◦ C, corresponds mainly to swelling of the granules, with limited leaching. Loss of birefringence, demonstrating that macromolecules are no longer oriented, occurs prior to any appreciable increase in viscosity. By contrast, differential scanning calorimetry (DSC) permits the determination of  the gelatinization temperature more easily and precisely than microscopy and, additionally, the energy input needed to disorganize the crystalline structure of  the granules. The second step, above 90 ◦ C, implies the complete disappearance of  granular integrity by excessive swelling and solubilization. Nevertheless this last transition is not detectable by DSC. Only at this stage the swollen granules can be destroyed by shear.  As observed by Donovan (71) and Colonna (72), at low water volume fractions (V 1 <  0.45) loss of crystallinity occurred by two (pea and high amylose maize) or three (standard maize) crystalline melting steps, according to the Flory equation (Fig. 2): 1/ T m − 1/ T mo = ( R/ H u )(V u / V 1 )(V 1 − X 1 V 1 ) where R  is the gas constant,  H u   the fusion enthalpy per repeating unit (anhydroglucose), V u / V 1   the ratio of the molar volume of the repeating unit to the molar volume of the diluent (water), T m  (K) the melting point of the crystalline polymer plus diluent, T mo  (K) the true melting point of undiluted polymer crystallites, V 1  the volume fraction of the diluent, and  X 1  the Flory–Huggins interaction parameter. At high water volume fractions, melting of crystallites and swelling  are cooperative processes. According to Colonna, during extrusion cooking and

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Fig. 1.   Effects of extrusion temperature on expansion ( ), breaking strength ( +), viscosity at 50◦ C (), water absorption index ( ), and water-solubility index (x) of extruded products from corn grits. Initial moisture content before extrusion was 18.2% by weight (69).

mainly under the conditions described by Mercier (water volume fraction  < 0.28) (68) starch undergoes a real melting. In the patent literature the term   destructurized starch (73–91) refers to a form of thermoplastic starch described as molecularly dispersed in water (92). Destructurization of starch is defined as melting and disordering of the molecular structure of the starch granules and as a molecular dispersion (75,92). The molecular structure of the starch granules is molten and consequently the granular structure disappears. This is achieved by heating the starch above the glass-transition and the melting temperature of its components until they undergo endothermic

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Fig. 2. Typical DSC curves for pea and maize starch. Water volume fractions (V 1 ): wrinkled pea (A), V 1 = 0.35; smooth pea (B) V 1 = 0.29; high amylose maize (C), V 1 = 0.20; and normal maize (D), V 1 = 0.55. Reprinted from Ref. 72, copyright 1985, with kind permission from Elsevier Science.

transitions. In the melt stage both the crystalline and the granular structure of  the starch are destroyed and the starch –water system forms a single phase in which no structure is discernible microscopically. The disappearance of the molecular structure of the starch granule may be determined using conventional light microscopy techniques (93). If starch is heated above the glass-transition and melting temperatures in presence of plasticizers, the endothermic transition can be replaced by an exothermic transition. Destructurized starch, in simple terms, is a form of thermoplastic starch suitable for applications in the sector of plastics, with minimized defects tied to the granular structure of native starch (17,94,98). Thermoplastic starch alone can be processed as a traditional plastic (69, 92,99); its sensitivity to humidity, however, makes it unsuitable for most of the

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Fig. 3. Some sorption isotherms of water vapor on native potato starch as reported in the literature (100).

applications (Fig. 3). Starch can be also made thermoplastic at water contents lower than 10%, in the presence of high boiling point plasticizers (14,17), to avoid expansion phenomena at the die.  Another term which can be found in the literature is  thermoplastically processable starch (TPS), defined as a thermoplastic starch substantially water-free.

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Table 1. Influence of Starch/EAA Ratio and of Partial Replacement of EAA with PE or PVOH on the Tensile Strength and Elongation of Starch/EAA Films a 

Starch, phr 10 30 40 40 40 40 40 40 a b

EAA, phr

PE, phr

PVOH, phr

Elongation, %

UTS, b MPa

90 70 60 40 25 20 55 40

— — — 20 25 40 — —

— — — — — — 5 20

260 150 92 66 85 34 97 59

23.9 22.2 26.7 23.9 21.7 20.1 32.0 39.7

From Refs. 112 and 118. Ultimate tensile strength.

Thermoplastically processable starch is a modified native starch which is obtained without water, since instead of water, use is made of a plasticizer or additive. The starch is thermoplastically processed together with the additive, and the thermal transition taking place here is exothermic (101 –106). Starch can be destructured in combination with different synthetic polymers to satisfy a broad spectrum of needs for the market. In this case it is possible to reach starch contents higher than 50%. Otey has studied EAA (ethylene –acrylic acid copolymer)/thermoplastic starch composites since 1977 (107 –117) and has demonstrated that the addition of ammonium hydroxide to EAA makes it compatible with starch. Urea, in these formulations, enhances the  film tear propagation resistance and reduces aging phenomena due to segmental motions in amorphous starch (118,119). The  films obtained with a content of plasticized starch of about 50% showed good tensile properties (Table 1) (112). The sensitivity to environmental changes and in particular the susceptibility to tear propagation precluded their use in most packaging applications (118); moreover, EAA is not biodegradable at all. In 1989 studies on EAA –thermoplastic starch films, containing 40% by weight of EAA, processed at water contents lower than 2%, led to improved processability and film properties with elongation at break up to 200% (93). By microscopic analysis it was possible to observe at least three different phases: one consisting of destructured starch, one consisting of the synthetic polymer alone, and a third one described as “interpenetrated,” characterized by a strong interaction between the two components. As a con firmation, phase changes observed by DSC, nuclear magnetic resonance (NMR) (113,117,120 –124), for starch–EAA –PE films showed at least four phases. DSC endotherms and extraction of free starch with hot water demonstrated the existence of a starch phase. DSC showed melting of an EAA phase and a low density polyethylene (LDPE) phase but did not indicate the presence of EAA in amorphous regions of the PE. NMR, X-ray diffraction, and extraction indicated the presence of an insoluble starch –EAA complex (124). It was demonstrated that a portion of the starch forms complexes (122,123) with EAA when EAA is salified by ammonium hydroxide or other salts during  extrusion cooking, providing partial miscibility between the two polymers. Rheological studies were performed on a product consisting of 60% starch and natural additives and 40% of an EAA copolymer, containing 20 mol % of 

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acrylic acid (125). A strong non-Newtonian behavior was shown by the viscosity curves at high shear rates; at intermediate shear rates the material seemed to approach a Newtonian plateau, whereas at low shear rates a viscosity upturn was observed, suggesting the presence of yield stress. Breaking-stretching data for the same material are also reported in the literature, together with those of LDPE (125). Starch/vinyl alcohol copolymer systems (126–131) can generate a wide variety of morphologies and properties, depending on the processing conditions, the starch type, and the copolymer composition. Different microstructures have been observed, from droplet-like to layered, as a function of different hydrophilicity of  the synthetic copolymer. Furthermore, for this type of composite, materials containing starch with an amylose–amylopectin ratio >20/80 wt/wt do not dissolve even with stirring in boiling water. Under these conditions a microdispersion, consisting of microsphere aggregates is produced; individual particle diameters are under 1 µm (Fig. 4). A droplet-like structure is also confirmed by transmission electron microscopic (TEM) analysis of  film slices (127). The droplet size is comparable with that of the microdispersion obtained by boiling. For these products, high melt elasticity is monitored by exit pressure data, whereas its recoverable fraction is almost negligible (low die swell) (129,130). The morphology of materials in film form, containing starch with an amylose – amylopectin ratio lower than 20/80 wt/wt, gradually loses the droplet-like form, generating layered structures (Fig. 5). In this case no microspheres are produced by boiling and the starch component becomes partially soluble. Fourier transform infrared (FTIR) second derivative spectra of materials with droplet-like structure, in the range of starch ring vibrations between 960 and 920 cm − 1 , gives an absorption peak at about 947 cm − 1 (Fig. 6). This peak, observed also when starch is

Fig. 4. Droplet-like structure of thermoplastic corn starch/EVOH blend in film from, after disagregation in boiling water (129).

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Fig. 5. Layered structure of thermoplastic waxy maize/EVOH film after 3 days of soil burial test (129).

Fig. 6. FTIR second derivative spectrum of corn starch: a, cystalline; b, gelatinized; c, blended with EVOH (129).

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STARCH Table 2. Insoluble Residue of Starch/EVOH 1:1 Films after Disagregation in Boiling Water as a Function of Starch Composition a 

Insoluble residue, b %

 Amylose content, % 5 10 15 20 25 28 70 a

From Ref. 129. starch plus EVOH

b Dry

58.3 67.5 75.3 92.1 97.5 96.8 97.1 =

100%.

complexed with butanol, is attributed (21) to ring vibrations, which result when amylose assumes a conformation known as the V form (a left-handed single helix). Therefore, the absorption at 947 cm − 1 does not correspond to crystalline or gelatinized amylose, but to a complexed one (V-type complex), as in the presence of  low molecular weight molecules such as butanol and fatty acid (21,129). Starchbased materials with an amylose content close to zero, even in the presence of  vinyl alcohol copolymers, do not show any peak at 947 cm − 1 , demonstrating that vinyl alcohol copolymers, as well as butanol, leave the amylopectin conformation unchanged. On the other hand, the V complex formed by starch, having an amylose – amylopectin ratio higher than 20 wt%, with ethylene–vinyl alcohol (EVOH) copolymers makes even amylopectin insoluble in boiling water (Table 2). The experimental evidence was accounted for by a model considering large invididual amylopectin molecules interconnected at several points per molecule as a result of hydrogen bonds and entanglements by chains of amylose –vinyl alcohol copolymer V  complexes (129). The biodegradation rate of starch in these materials is inversely proportional to the content of amylose–vinyl alcohol complex. Furthermore FTIR second derivative spectra show the 947 cm − 1 peak increasing with biodegradation, which means a delayed microbial attack of complexed amylose relative to amylopectin (129). In addition, water permeability of starch/EVOH  films is a function of the V-type complex and can range from about 2.46 –1 g · cm/m2 · day 820–334 g · 30  µ m/m2 · 24h (130) (see B ARRIER P OLYMERS for units).  A general study of shear flow characteristics was performed on a material containing about 60% of starch and natural additives and 40% of ethylene–vinyl alcohol copolymer 40/60 mol/mol (131). A strong pseudoplastic behavior at high shear stresses as well as yield stress at lower ones was detected (Fig. 7). The nonlinear Bingham fluid model (132) well described its viscous behavior over a wide range of shear rates. High levels of melt elasticity were detected from steady shearing tests, whereas its recoverable fraction was almost negligible, at least for a reasonable time scale. The peculiar viscous and elastic behavior has been explained on the basis of the droplet-like morphology generated by the ability of  starch to form V complexes in the presence of EVOH. Notwithstanding the peculiar rheological behavior shown by starch/EVOH systems, traditional processing  techniques such as film blowing can be easily applied.

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Fig. 7. Shear stress ( , ) and normal stress difference (N11 /ex) ( , ) versus wall shear rate of a thermoplastic starch/EVOH blend at 140 (open circles/squares) and 150 ◦ C (filled circles/squares) (131).

The products based on starch/EVOH show mechanical properties good enough to meet the needs of speci fic industrial applications (133). Their moldability is comparable with that of traditional plastics such as polystyrene (PS) and acrylonitrile–butadiene–styrene copolymer (ABS). Nevertheless, they continue to be highly sensitive to low humidities, especially when in film form, with evident embrittlement. In terms of biodegradation, 10 months of aerobic biological treatment, performed by a high sensitivity respirometric test, provoked the degradation of more than 90% wt/wt of a product constituted by 60% of maize starch and natural additives and by 40% of EVOH copolymer at 40% mol/mol of ethylene. Furthermore, it has also been demonstrated that the synthetic component was degraded to about 80% wt/wt, notwithstanding interrupting the test when CO 2  evolution was still relevant (127,128). A material with the same composition, containing  an EVOH copolymer, characterized by a lower ethylene content (29% instead of  40% mol/mol) and, therefore, by a reduced ability to generate interpenetrated structures, showed, in the Sturm test, an initial biodegradation rate signi ficantly higher (127). The semicontinuous activated sludge (SCAS) test and biodegradation in lake water of a product constituted of 70% maize starch and natural additives and 30% EVOH support the hypothesis of substantially different biodegradation mechanisms for the two components (128): (1) the natural component, even if significantly shielded by the interpenetrated structure, appeared to be initially hydrolyzed by extracellular enzymes;

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Other evidences for disappearance of ethylene–vinyl alcohol copolymers have been produced to a limited extent by Roemesser (134) and Kaplan and co-workers (135). The presence of starch improves the biodegradation rate of these synthetic polymers; a fundamental role is also played by size and distribution of ethylene blocks. The degradation rate is too slow to consider these materials as compostable (128). Specific types of plasticizers were selected in order to avoid migration phenomena and physical aging (133). The possibility of speeding up the biodegradation process was considered by modifying the ethylene–vinyl alcohol copolymer by introducing carbonyl groups, making it more sensitive to photodegradation (136). The transparency of the material was also improved by adding additives such as boric acid, borax, and other saline compounds (137). Surface treatment by wax lamination or coextrusion was also considered (138). With this kind of material it is possible to obtain finished parts by film blowing, injection molding, blow molding, thermoforming, etc. It is also possible to make foamed parts (139), particularly by an expansion process based on injection molding technology. The technology consists of a breathable mold connected with a vacuum pump, applied to an ordinary injection molding madrine (140). Cushioning characteristics of these materials are close to expanded polystyrene (EPS-55) (Fig. 8); moreover, the foam density is of 0.040 g/mL. Starch can also be destructured in the presence of more hydrophobic polymers such as aliphatic polyesters (141). It is known that aliphatic polyesters with low melting points are dif ficult to process by conventional techniques for thermoplastic materials, such as film blowing and blow molding. With reference particularly to poly(ε-caprolactone) and its copolymers, films produced thereby are tacky as extruded, and rigid, and have low melt strength over 130 ◦ C; moreover, because of the slow crystallization rate of such polymers, the crystallization process proceeds for a long time after production of the  finished articles with an undesirable change of properties with time. Novamont’s Mater-Bi starch-based technology implies processing conditions able to almost completely destroy the crystallinity of amylose and amylopectin, in the presence of macromolecules which are able to form a complex with amylose such as specific polyesters. They can be of natural or synthetic origin and are biodegradable. The complex formed by amylose with the complexing agent is generally crystalline, and it is characterized by a single helix of amylose formed around the complexing agent. Unlike amylose, amylopectin does not interact with the complexing agent and remains in its amorphous state. The speci fication of  the starch, ie, the ratio between amylose and amylopectin, the nature of the additives, the processing conditions, and the nature of the complexing agents, allows engineering of various supramolecular structures with very different properties. The scheme of a “droplet-like”   and a “layered”   structure which can be produced as a result of Mater-Bi technology is reported in Figures 9 and 10. The droplet-like structure (Fig. 9) is constituted by a core of an almost amorphous

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Fig. 8. Dynamic cushioning properties of Mater-Bi molded foams. , Mater-Bi molded foam; , EPS-55. Reprinted from Ref. 140, copyright 1994, with kind permission from Elsevier Science.

Fig. 9. Mater-Bi technology: droplet-like structure. Green, amylopectin; red, amylose; blue, complexing agent.

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Fig. 10. Mater-Bi technology: layered structure. Green, amylopectin; red, amylose; blue, complexing agent.

amylopectin molecule screened by complexed amylose molecules which render amylopectin insoluble (142–144). The layered structure is constituted by submicronic layers of amylopectin molecules intercalated by layers of complexing agent; such layers are compatibilized by complexed amylose (Fig. 10). The two structures and the many others derived from them explain the wide range of mechanical, physical-chemical, and rheological properties and the different biodegradation rates of Mater-Bi products. Blending of starch with aliphatic polyesters improves their processability and biodegradability. Particularly suitable polyesters are poly(ε caprolactone) and its copolymers, or polymers of higher melting point formed by the reaction of  1,4-butandiol with succinic acid or with sebacic acid, azelaic acid, or poly(lactic acid), poly(hydroxyalkanoates), and aliphatic–aromatic polyesters. The compatibilization between starch and aliphatic polyesters can be promoted either by the processing conditions and or by the presence of compatibilizers between starch and aliphatic polyesters such as amylose/EVOH V-type complexes (129) and starch-grafted polyesters. Chain extenders like diisocyanates, epoxides, etc. are preferred. These types of materials are characterized by excellent compostability and mechanical properties and reduced sensitivity to water. Thermoplastic starch can also be blended with polyolefins (145). In this case, about 50% of thermoplastically processable starch is mixed with 40% of polyethylene and 10% of ethyl acrylate–maleic anhydride copolymer. During this mixing  process an esterification reaction takes place between the maleic anhydride groups in the copolymer and the free hydroxyl groups in starch. Other studies have been performed on polyamide/high amylose (75,146,147) and acrylic copolymers/high amylose starch systems (75,147,148). The problem of partial biodegradability and a too high sensitivity to humidity persists. Starch/cellulose derivative systems are also reported in other publications (137,141,149,150), particularly, cellulose acetate and butyrate/starch blends in presence of glycerol and epoxidized soybean oil (149). The combination of starch with a water-soluble polymer such as poly(vinyl alcohol) (PVOH) and/or polyalkylene glycols has been widely considered since 1970 (151). More recently, the thermoplastic starch/PVOH system has been mainly studied for producing starch-based loose fillers as a substitute for expanded polystyrene (152–158). As an example, Altieri and Lacourse developed a technology based on hydroxy propylated high amylose starch containing small amounts of 

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PVOH for improving foam resiliency and density (152 –156). In this case loose fill was produced directly by a twin-screw extruder. More advanced processes and alloys have been developed which have resulted in foams with lower foam densities (8–6 kg/m3 ) and better performance (159 –161).

Starch-Based Materials on the Market The market of destructurized and complexed starch-based bioplastics accounts for about 25,000 ton/year, 75% of which is for packaging applications, including soluble foams for industrial packaging and films for bags and sacks. The market share of these products accounts for about 75–80% of the global market of bioplastics (162). Leading producers with well-established products in the market are Novamont, National Starch, main Novamont partner and licensee in the sector of  loose-fills and of foamed sheets, and,  finally, Biotec with a capacity of about 2000 ton/year. Following the recent start-up of its third line dedicated to the production of Mater-Bi film grades in Terni, Novamont’s internal production capacity is of  20,000 ton/year. The total capacity, including the network of licensees in the sector of loose fills, is about 35,000 ton/year. The technology for the production of starchbased loose fills is licensed together with National Starch and Chemical Co. The wide patent portfolio of Novamont covers the technologies of complexed starch developed by Novamont and of destructurized starch developed by Warner Lambert and acquired by Novamont in 1997 after the exit of Warner Lambert from the market in 1993. Moreover, on August 2001 Novamont acquired the  film technology of Biotec which included an exclusive license of the Biotec ’s patents on TPS in the sector of  film (162). In recent years companies such as Earthshell, Apack, and Avebe dedicated significant efforts to the development of food containers through the  “baking technology.” Market tests are in place in the United States and Europe to check their performances (163). Moreover, very recently in the Netherlands, Rodemburg built up a plant for the transformation of potato wastes generated by the industry of  fried potatoes in a granulate to be used for the injection molding of slow release devices. The claimed capacity is 40,000 ton/year. The price of starch-based bioplastics ranges from 1.25 to 4 Euro/kg, with possibilities to compete even with traditional materials in some limited areas (163). The properties achieved by starch-based bioplastics in certain applications and the commitment of the companies today dealing with this family of bioplastics give more confidence in the future possibilities of this market sector. Bioplastics from renewable origin, either biodegradable or nonbiodegradable, still constitute a niche market which requires high efforts in the areas of material and application development; the technical and economical breakthroughs achieved in the last three years, however, open new possibilities for such products in the mass markets. Novamont today boasts a diversified portfolio of industrial tailor-made materials for a wide range of applications, which explains its position as market leader (162).

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 After more than 12 years of research and development, Mater-Bi products are able to fulfil specific in-use performances in different application sectors, and offer original solutions both from the technical and the environmental point of view. Under the Mater-Bi trademark today, Novamont produces a wide range of  materials, divided into five families, according to the processing technologies: film, extrusion/thermoforming, injection molding, foaming, and tires technology. MaterBi products are mainly used in specific applications where biodegradability is required; examples include composting bags and sacks, fast food tableware (cups, cutlery, plates, straws, etc), packaging (soluble and insoluble foams for industrial packaging), film wrapping, laminated paper, food containers, agricultural film products (mulch film, nursery pots, plant labels, slow release devices, etc.), and hygiene (diaper backsheet, cotton swabs). New sectors are also growing outside biodegradability, driven by the unique technical performance of some Mater-Bi products versus traditional materials, as in the case of breathable films with silky hand for diapers, chewable items for pets, or biofillers for tires. The new tire Biotred GT3, launched by Goodyear in 2001 and recently adopted by BMW and Ford, is an example of the high tech performances reached by Mater-Bi products (164). Mater-Bi starch-based materials are characterized by the following  properties: (1) complete biodegradability and compostability according to existing standards (Fig. 11) (165–167) (2) significant reduction of environmental impact, particularly with respect to CO2   emissions and energy consumption, in comparison with traditional materials in specific uses (168,169) (3) in-use performances similar to traditional plastics (4) processability similar or improved in comparison with traditional plastic materials (162).

Fig. 11. Aerobic biodegradation of Mater-Agro under controlled composting conditions (EN13432), in comparison with pure cellulose (test performed by OWS, Belgium). , positive control; , Mater-Bi.

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Table 3. Some Physical Properties of Mater-Bi Grades for Film, in Comparison with Traditional Plastics Test

Procedure

MFI Strength at break Elongation at break  Young ’s modulus Tear strength Primer Propagation

ASTM D1338 ASTM D882 ASTM D882 ASTM D882 ASTM D1938

Unit

Mater-Bi

LDPE

g/10 min MPa c % MPac

2–8a 24–30 200–1000 100–400

0.1–22b 8–10 150–600 100–200

N/mmd N/mmd

30–90 30–90

60 60

a

150◦ C, 5kg. 2.16 kg. c To convert MPa to psi, multiply by 145. d To convert N/mm to ppi, divide by 0.175. b 190◦ C,

Other properties of Mater-Bi  films of the last generation can be summarized as follows: (1) soft, silky handle (2) wide range of permeability to water vapor from 0.75 to 3 g  · cm/m2 · day (250 to 1000 g · 30µm/m2 · 24h) (3) wide range of mechanical properties from soft and tough materials to rigid ones, with no significant aging after one year of storage, (163) (Table 3 and 4) (4) antistatic behavior (5) colorability with food contact approved pigments (6) compostability in a wide range of composting conditions: from home composting and static windrows to rotary fermenting reactors They are biodegradable and compostable according to the present European standards and are certified by AIB Vincotte in Belgium, by DINCERTCO in Germany, and by IIP in Italy, according to CEN EN13432, DIN 54900, and Table 4. Some Physical Properties of Mater-Bi Grades for Injection Molding, in Comparison with Traditional Plastics Test

Procedure

MFI Strength at break Elongation at break  Young ’s modulus IZOD (notched impact)

ASTM D1238 ASTM D638 ASTM D638 ASTM D638 ASTM D256

a

170◦ C, 5 kg. b 23◦ C, 2.16 kg. c 200◦ C, 5 kg. d To convert MPa to psi, multiply by 145.  e To convert kJ/m 2 to ftlbf/in 2 , divide by 2.1.

Unit

Mater-Bi a

PPb

PSc

g/10 min MPa d % MPa kJ/m2 e

20–10 20–30 20–500 200–2000 1–80

0.3–40 23 400–900 1400–1800 3–10

1.2–25 30–60 1–4.5 3000–3500 2–3

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UNI 10785 standards, respectively (see D EGRADABLE POLYMERS AND PLASTICS IN L ANDFILL S ITES).  After the acquisition of Enpac in 1998 and the subsequent agreement with Novamont, National Starch is licensing two technologies for the production of  loose fills: one from hydroxypropilated high amylose starch and a second from almost unmodified starch. The loose fills’ densities range from 6 to 10 kg/m 3 . The main licensees are Unisource, American Excelsior, Storopack, and Flow Pack in the United States. Biotec, the German company which acquired in 1994 the patents of Fluntera, was acquired by EKI (Essem Kashoggi Industries) in 1998. Biotec, after the sale of  the film business to Novamont in 2000 is concentrated on foodserviceware products and on pharmaceutical products.

Conclusions Starch-based bioplastics constitute a new generation of materials able to significantly reduce the environmental impact in terms of energy consumption and green-house effect in specific applications, to perform as traditional plastics when in use, and to completely biodegrade within a composting cycle through the action of living organisms when engineered to be biodegradable. They offer a possible alternative to traditional materials when recycling is inpractical or not economical, or when environmental impact has to be minimized.  After more than 12 years of research and development, starch-based materials have begun to fulfil specific in-use performances in different application sectors. They are able to offer original solutions both from the technical and the environmental point of view. Today some of the bioplastics available in the market are used in speci fic applications where biodegradability is required, such as the sectors of composting  (bags and sacks), fast food tableware (cups, cutlery, plates, straws etc), packaging  (soluble foams for industrial packaging, film wrapping, laminated paper, food containers), agriculture (mulch film, nursery pots, plant labels), hygiene (diaper back sheet, cotton swabs) and slow release devices in agricultural and pharmaceutical sectors. Moreover, new sectors are growing outside biodegradability, driven by improved technical performances versus traditional materials, as in the case of  biofillers for tires and chewable items for pets. The price of bioplastics from renewable origin is decreasing and ranges from 1.25 to 4 Euro/kg, with possibilities to compete even with traditional materials in some limited areas. The world market for biodegradable plastics is still small, but it has grown significantly in the last few years, reaching about 33000 ton/year in the year 2000; products totally or partially from renewable resources represent nearly 85 –90% of this market (170).

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158. Int. Pat. Appl. WO 92/08759 (July 29, 1992), J. R. Anfinsen and R. R. Garrison (to DuPoint, US). 159. Eur. Pat. Appl. 0 667 369 (Aug. 16, 1995), C. Bastioli, V. Bellotti, G. Del Tredici, and  A. Rallis (to Novamont Spa, Italy). 160. Eur. Pat. 0 696 611 (Feb. 14, 1996), C. Bastioli V. Bellotti, G. Del Tredici, A. Montino, and R. Ponti (to Novamont Spa Italy). 161. Eur. Pat. Appl. 0 696 612 (Feb. 14, 1996), C. Bastioli V. Bellotti, G. Del Tredici, and A. Rallis (to Novamont Spa, Italy). 162. C. Bastioli and S. Facco, in Biodegradabile Plastics 2001 Conference, Frankfurt, Germany, Nov. 26–27, 2001. 163. C. Bastioli, in Global Status of the Production of Biobased Materials, Actin Conference, Birmingham, U.K., 2001. 164.  Automotive News Eur. 15 (Oct. 22, 2001). 165. Prufung der Kompostierbarkeit von Kunstoffen, DIN V 54900-2, 1998. 166. Requirements for Packaging Recoverable through Composting and Biodegradation — Test Scheme and Evaluation Criteria for the Final Acceptance of Packaging, EN 13432. 167. Compostabilita’ dei Materiali Plastici—Requisiti e Metodi di Prova, UNI10785, Jan. 1999. 168. Life Cycle Assessment of Mater-Bi Bags for the Collection of Compostable Waste, Composto, Switzerland, 1998. 169. Life Cycle Assessment of Mater-Bi and EPS Loose-Fills, Composto, Switzerland, 2000. 170. Actual Situation and Prospects of EU Industry using Renewable Raw Materials, E.1, 2002. Edited by DG Enterprise.

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