1. INTRODUCTION
Plastic packaging materials perform an important role in the food industry due to their toughness, light weight and flexibility that ceramic and metals cannot meet (1). Nevertheless, the environmental effect caused by traditional plastics materials mainly associated with the waste-disposal problems due to their low biodegradability and the impediment of recover all the plastic used to be recycled (2) , has promoted to develop environmentally-friendly commodities (3), (4). Nowadays, the industry is looking forward to introduce biodegradable polymers in the market, aiming to replace the oil-based materials, and contributing with solutions to the environmental problems (5).
Biodegradable polymers are defined as polymers which can be transformed in dioxide carbon, water , methane and other low molecular-weight products after crossing a degradation process, which takes place through the presence of living organisms (bacteria, fungi , yeast, algae, insects, etc.) (6) at specific conditions of light, temperature, oxygen (aerobic or anaerobic conditions), etc.(7) (8), (9). Nonetheless, the influence of polymer chemical structure and its origin are remarkable at the degradation process too (3). The time that the biodegradation needs to take place ranges between few weeks to several months, depending on the environmental conditions and the inherent polymer molecular structure (6).When these kind of polymers are degraded , the production of harmful substances is reduced because the residues can be incorporated at the geochemical natural cycle (10),(9).
Bio-based and biodegradable polymers have an extensive range of applications such as pharmaceutical, biomedical, horticulture, agriculture, consumer electronics, automotive, textiles and packing, the latter being perhaps one of the most common application (11). To date, many biodegradable polymers are available namely, poly(lactic acid) or polylactides (PLA), polycaprolactone (PCL), poly(butylene adipate terephthalate) (PBAT), polyhydroxybutyrate (PHB), polyhydroxyalkanoates (PHAs), polyesteramide (PEA) (12),(4). Nonetheless, in some cases its high cost of production prevents them from being considered as substitutes for traditional polymers (13). An attractive alternative is the development of biomaterials from natural, low cost materials because of their extensive availability and renewable character. In this sense, starch-based materials constitute an interesting approach to obtain environmental-friendly materials with potential massive use (13).
Starch is a polysaccharide coming from tubers, roots and cereals, which has an important role as food ingredient but it is starting to be used at industry, i.e. paper and board sector, industrial binder sector, pharmaceutical sector and textile industry (14) . Native starches experiment high degradation rates, though there are shortcomings associated to its poor mechanical properties and processability problems (15) (16) (17). Therefore, some methods to fulfill all industry´s requirements have been studied in order to improve functional properties e.g. modification (i.e. physical, chemical, enzymatic and genetical modifications) (18), plasticization and starch blends with biodegradable polymers, which seems to be the most promising innovation in order to enhance mechanical and thermal properties (19) (17). Besides, different types of nanoreinforcements like nanofibers, nanocrystals and starch nanocrystals are also been investigated during the last decade (20).
Referring to packaging films , it is know that they have to show specific characteristics of strength, rigidity and permeability, which can’t be reached by a material composed entirely of starch , in spite of that the starch blends with biodegradable polymers allows the material to achieve the requirements mentioned above (21).In general terms the blending of biodegradable polymers allows to reduce the cost of the materials and take control of the properties and rate of biodegradability desire at the final product (22). Therefore, the aim of this review is to summarize succinctly the current state of art of the topics related to starch blends with biodegradable polymers in packaging materials.
2. TYPES OF BIODEGRADABLE POLYMERS
The biodegradable polymers are classified in two important groups according to their origin: biologically derived or natural polymers and synthetics polymers(23). Natural biopolymers come from living organisms , meaning that they are available in large quantities from renewable sources , on the other hand the synthetic polymers are man-made which means they are produced by non renewable sources like petroleum, coal or natural gas (24),(3). However, there is not a clear cut line separating these groups, e.g. poly (glycol acid) can be obtained by synthetic process produced from oil-derived starting materials or by fermentation process due to live organisms (25) . This paper will consider “synthetic” as man-made.
2.1 Natural polymers
2.1.1 Biodegradable polymers obtained by through fermentation
Mainly these group is related with polyesters and neutral polysaccharides produced by microorganisms when they have the access to a feed reserve of carbon and energy source (6). Nowadays the market presents an important advanced in the research of polyhydroxyalkanoates (PHAs) , that is a group of hydroxybutyric acid and hydroxyvaleric acid. (PHA)s are high molecular weight and the main chain can presents n-alkyl substitutions. In general terms these polymers has a slow rate of biodegradability (on the order of years) ,are biocompatible and thermoplastics (25).
The most studied compounds of this group is poly(3-hydroxyburtyrate) (PHB), obtained as a result of fermentation by the bacterium Alcaligenes eutrophus, and also poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV ) (3).
The latest research of PHB production, opens the possibility to obtained it from water hyacinth which is one of the most notorious aquatic weeds. One of the most important advantages of this compound is its heat tolerance with a melting point around 175°C , which allows application in packaging films (26).
2.1.2 Biodegradable polymers from chemically modified natural products
In this group highlights the polysaccharides, polymers formed by many sugar units (glucose and fructose) ; the join of these monomers results in the formation of polymeric material (25). In this group we can find the cellulose and the starch , which have been the most studied materials because of their potential of replace the oil based- polymers at in large scale and low cost (27).
Starch is a cheap abundant material, nevertheless ,the main problem associated with starch is their poor mechanical properties and water solubility, that is why some developments proposed techniques like plasticization, or blends in order to produce competitive commercial commodities (28).
Cellulose is a consistent material that comes from vegetable sources, in comparison with starch , it is relative resistance to biodegradation, however cellulose can be degraded at aerobic or anaerobic conditions (6).
2.2 Synthetic polymers
These group contemplate materials that come from petroleum sources nevertheless after a process of polymerization their become in a biodegradable polymers following the EN 13432 rule for the biodegradability(29) These type of biopolymers in general are biologically inert and present predictable properties. Furthermore, they can be produce in mass (23), (2).
Polyesters are the most representative polymers of this group; in turn they can be classified in aliphatic and aromatics. Corresponding to the aliphatic polyesters group can be mentioned for example poly(caprolactone) (PCL), poly(lactic acid) (PLA), poly(butylenes succinate) (PBS), poly(butylenes succinate adipate) (PBSA), poly(glycolic acid) (PGA), and poly(vinilalcohol) (PVA), the main problem associated with them is their melting point around 60°C , which excluded them for some applications (29). Aromatic polyesters include polyesters containing aromatic rings or cyclic ether moieties (30).
PLA is one of the most studied compounds because of its high biodegradability, biocompatibility , good processability and relatively low cost (31). Industrially, companies like Chronopol ,Feberweb , Cargill Dow LLC and Mitsui Chemicals, produces and commercialists PLA (6). The synthesis of this polymers occurs at many step but mainly consists in the production of lactic acid by bacterial fermentation and the follows the polymerization(26). In order to improve the properties of PLA it has been blend with several hydriphhilic polymers, i.e. poly(ε-caprolactone) (PCL), poly(vinyl alcohol) (PVA), poly(ethylene glycol) (PEG), pluronic [triblockcopolymersof PEG and poly(propylene oxide), hyaluronicacid, and poly(vinyl acetate) (PVAc) (32).
PCL is obtained by chemical synthesis from crude oil, commercially has been used extendly in packaing industry for make compostable bags, nonetheless a material based only in PCL is not economically rentable, this is why nowadays PCL is mixed with an amount of natural biopolymers (6).
PVA has excellent gas barrier properties, high strength , tear , adhesive, flexibility , water absortion, and boding characteristics (33). Industrially is used in manufacturing of biodegradable films and in the production of adhesives or paper coatings (6).
REFER
3. STARCH BLENDINGS
Starch is usually plasticized before the blending process (34), (28). By plasticization a thermoplastic starch (TPS) can be obtained , which is principally characterized by the destructurization of the semi-crystalline structure of native starch(35). Depending on the nature of the plasticizer added to the starch, the final properties of the thermoplastic starch (TPS) can differ. In general terms plasticizers produce an increase of the flexibility and fluidity by reducing the strong molecular chain interactions; additionally, there is an increase of permeability against moisture, also a reduction of density and viscosity on account of increasing both free volume and chain movements (36) (37) (38). Although not all of these properties can be necessarily obtained at the same time and unfortunately TPS still remains being a very hydrophilic material (28).
Blending TPS with biodegradable polymers is one of the most promising advancements for possible applications in food packaging (39). In general terms, blending aims to reduce the production cost, improve the barrier properties, mechanical properties, dimensional stability, decrease the hydrophilic character of starch, and increases the biodegradability(34), (28). When macromolecules (e.g. PVA, PLA, PCL, PHB, PBSA, etc) are blended with TPS or native starch, they form a complex with amylase giving as a result a starch blend; it is important to state that amylopectin doesn’t not interact, remaining in its amorphous state (40).
3.1 Starch/PVA
Gelatinization is a common method to blend starch with PVA; other methods might not be useful due to the close gap between the thermo-degradation temperature and the melting temperature (38). One important fact is the compatibility they share (because both components are polyols), it enables them to form a continuous phase at blending(39). Referring to the biodegradability, starch and PVA are biodegradables in several microbial environments, nevertheless the biodegradability of PVA depends on its degree of hydrolysis and its molecular weight. (39),(41).
The presence of PVA in the blend, increase mechanical strength, water resistance, weatherability, (38). In this blend, both PVA and starch can be plasticized into a thermoplastic material, commonly using the casting method (42) and glycerol in aqueous medium as a plasticizer.
3.2 Starch/PLA
Owing to the low miscibility between TPS and PLA, the addition of some substances is required, i.e. compatibilizers, amphiphilic molecules, or coupling agents accompanied of good melt-blending techniques (34). Poly(hydroxyester ether), methylenediphenyl diisocyanate (MDI), PLA-graft-(maleic anhydride), PLA-graft-(acrylic acid)10 and PLA-graft-starch and poly(vinyl alcohol) have been used as a compatibilizers in this blend (43). Wang et al. (9) mentioned that there is not a major change at transition temperature (Tg) with the addition of starch at PLA, and both the tensile strength and elongation of the blend decrease (9).
3.3 Starch/PCL
PCL is a hydrophobic biodegradable polyester, hence at the blending stage, between it and the starch, an undesirable phase separation is occurs (44). In order to increase the compatibility between both composites, the addition of an interfacial agent or compatibilizer is necessary. Sugih et al. (44) assessed the behavior of two interfacial agents, PCL-g-glycidyl methacrylate (PCL-g-GMA) and PCL-g-diethyl maleate (PCL-g-DEM) in PCL/starch blend, meanwhile Singh et al. (45) mention the introduction of poly(ethylene glycol) (PEG) into PCL to improve interfacial properties.
Benefits obtained in this blend are evident; adding PCL allows to overcome the weakness of pure TPS and starch, also the reduction of the crystallinity of PCL favored the enzymatic degradation at the same time (46), (47).
3.4 Starch/PHB-HV
Reis et al. (48) assesses blends of polyhydroxybutyrate-hydroxyvalerate (PHB-HV) with maize starch at different contents prepared by casting, but the blends showed a lack of interfacial adhesion between starch and PHB-HV, and heterogeneous dispersion of starch granules over the PHB-HV matrix. This shortcoming could be reduced by precoating the starch with poly(ethylene oxide) (PEO), improving the adhesion between PEO –PHBV(9).
3.5 Starch/PBSA
The addition of starch to PBS helps to improve its flexibility and reduces its biodegradation time; this way is possible to expand its applications in packaging and flushable hygiene products (9), (49).
3.6 Ternary Blends
Liao and Wu (32), studied ternary blends between PCL, PLA and starch (with acrylic acid grafted PLA70PCL30 as compatibilizer) to overcome the shortcomings of brittle and processing properties; and also to reduce the overall cost.
Rahmah at al. (50) present a research related with a hybrid blend compounded by low density polyethylene (LLDPE) , PVA and starch, where the mechanical and thermal properties are evaluated.
4. PREPARATION OF STARCH/BIODEGRADABLE BLENDS
4.1 Hydrogels
Hydrogels are defined like a hydrophilic polymer web able to soak up large quantities of water (51). Xia et al.(52) and Zhai et al. (51) assessed the preparation of starch-PVA hydrogels and their properties.
4.2 By Casting
Mainly consist in an aqueous suspension where either starch and biodegradable polymers are mixed and then it is spread on a hot anti-adhesive coated maintained at specific temperature where the water evaporation occurs, leaving as a result the blend film(53). In spite of the simplicity of this method, it can be used only as lab scale process (20). Buscar info adicional del por qué??
4.3 Gelatinization/crystallization
This technique is used when the thermal degradation temperature of the biodegradable polymer is near to its melting temperature, and mainly consist in the gelatinization of starch and polymer in the presence of cross-linking agent or plasticizer and water (9). The gelatinization is referred to the lost of the semi-crystallinity of starch granules due to the water at specific temperature inherent to the type of starch (54). Explicar desde el punto de vista de la gelatinization.
4.4 Reactive blending
Blending/extrusion usually takes place at specific conditions that promotes the chemical interaction between the functional groups corresponding both the compatibilizer and the biopolymers (55). Chemically , reactive blending implies the covalent bonding by Van der Walls forces between starch and the biopolymer (40).
4.5 Irradiation/cross-linking
Recently, irradiation is one of the techniques used to promote the chemical reaction between the polymer molecules (cross-linking). In this sense, Mubarak et al. (56), present a study of a PVA/ starch blend cured by UV- radiation. UV- irradiation produces the modification of the surface properties, Sionkowska (57) studied its effect of PVA surface .
There are different types of irradiation e.g. UV irradiation, γ-irradiation, electron beam irradiation and ultrasonic treatment. The first one requires the presence of photo sensitizers (e.g. benzoic acid family) to induce changes at the substrate; the second one is a ionic , non heating environmentally – friendly cross-linking agent of starch that improve functional properties; the third one consist in an excitation technique caused by the generation of radicals product of the breaking of the H=C bonds that mainly induce the compatibility between polymers, and the last one consist in the use of sounds waves beyond the audible frequency range (>20kHz) which is useful to improve the chemical activity (58).
It is important to keep in mind that irradiation is not only a blending technique, it can also be used as a modification starch process. Gani et al . (59) studied the effect of γ-irradiation on functional and morphological bean starch properties , resulting in the reduction of :amylose content , swelling index , pasting properties , syneresis; and in the increase of solubility index, transmittance and water absorption.
Que dependiendo del tipo de procesamiento puede ocurrir la modif de uno o más componentes de las mezclas.
5. CHARACTERIZATION
Food packing materials need to exhibit specific characteristics or properties, mentioned e.g. optical properties, resistance, moldability and barrier to light, water, Vilpoux and Avérous (60). all of them requires an specific technique to be quantified, so, this review will describe some of the most relevant ones.
Decir que solo se va a describir para que sirve y no como se hace
MORPHOLOGIAL CHARACTERIZATION
5.1 Differential Scanning Calorimetry (DSC)
This technique allows to analyze the crystalline structure of the polymeric blend, by showing the enthalpy changes occurred while the melting (22). The thermal study mainly permits to identify the glass transition (Tg) and the melting temperatures (Tm), and then compare them with a 100 % crystalline standard in order to determinate the degree of crystallinity (61), (46). In addition DCS, is useful to determinate the miscibility degree between composites of the blend; therefore if its only one single phase, it would be directly related with a single glass transition temperature (22).
5.2 Scanning electronic microscopy (SEM)
Especificar q la fractura se relaciona con la mezcla
This technique allows to observe the surface morphology including possible fractures, Arrieta et al. (62) mentioned the use of this technique at their studies, to observed the microstructure at the film by covering the film with a layer of gold in order to attenuate the reflectance.
5.3 X-ray diffraction
This technique allow to analyze the crystalline structure of the sample, Belibi et al. (63) used this method and talks about the Bragg´s law like a source to calculate the distance between the planes of crystal based on diffraction angles.
MECHANICAL PROPERTIES
This test is basically based on the analysis of the Young´s module and the capacity and the elongation at break performed on mechanical tensile tester or a dynamometer (63). The ageing and the storage conditions (e.g. temperature and relative humidity of storage´s environment) of sample is determinant at this test, hence, it is important to maintain the same conditions during a several period until make it (47).
At this kind of test the generation of a stress-strain curve is determinant to evaluate the variations in at young´s modules and yield point depending of the percentage of substances at the blend (61).
Hacer énfasis en tracción
6. NANOCOMPOSITES
Introducir con un párrafo
6.1 Nano composites- fillers in starch matrix
The addition of nanocomposites to reinforce the starch blends is one of the latest advances , this nanocomposites can be made by using inorganic or natural materials and can be defined like thermoplastics polymers with a charge between 2-8 % of nano scale inclusions (64). Ojo revisar ref
Nano fillers can be presented in different ways: nanoparticles (spherical or polyhedral), nanotubes, and nanolayers , in all cases exhibiting a large superficial area that improves de adhesion between the composites of polymer blend (65).
Xie et al. (66) shows a completely review about different types of nano fillers in plasticized starch-based matrix, the mainly are phyllosilicates (montmorillonite, hectorite, sepiolite, etc.), polysaccharide nanofillers (nanowhiskers/nanoparticles from cellulose, starch, chitin, and chitosan), carbonaceous nanofillers (carbon nanotubes, graphite oxide, and carbon black), and many more. This work concludes that the most utilized nano fillers are phyllosilicates due to their availability, low price, and high aspect ratio. On the other hand polysaccharide nano-fillers required acid hydrolysis at their preparation, reason why their use is non ecological friendly.
Principal properties affected by the addition of nano fillers in starch-based materials are: the improve of thermal stability, increase of biodegradation rate an oxygen barrier and the reduction of hydrophilicity(63), (66).
6.2 Starch- based nanocrystals
Starch nanocrystals are prepared with native starch granules brought under hydrolysis during an extended time but not exceeding the gelatinization temperature; this procedure causes the hydrolyzation of the amorphous regions releasing the crystalline lamellae (58). Nowadays this type of nano- filler have take force because of its low cost (abundance of starch) , renewability and eco friendly characteristics (58).
Le Corre et al. (67) reviewed the use of starch nanocrystals as reinforces of elastomer-based matrix , showing a positive reinforcing effect evidenced by the increase of both stress at break and relaxed storage modulus.
The main aspects that highlight by the addition of starch-based nano-biocomposites are the increase of values of strength at break an Tg, but also their disadvantages associated e.g. the increment of water absorption and decomposition temperature (66).
Poner aplicaciones
7. REFERENCES
1. Kutz, Myer. Handbook of Environmental Degradation of Materials. Waltham : Elsevier, 2012.
2. Chemical syntheses of biodegradable polymers. Okada, Masahiko. Aichi, Japan : s.n., 2002, Progress in Polymer Science, Vol. 27, págs. 87-133.
3. Biodegradable Polymers. Vroman, Isabelle y Tighzert, Lan. 2, 2009, Materials, Vol. 2, págs. 307-344.
4. Recycling of bioplastics, their blends and biocomposites: A review. Soroudi, Azadeh y Jakubowicz, Ignacy. 2013, European Polymer Journal .
5. Starch Based Biofilms for Green Packaging. Ali, Roshafima R., y otros. [ed.] Engineering and Technology World Academy of Science. Skudai, Malaysia : s.n., 24 de 10 de 2012, Vol. 6, págs. 508-512.
6. Biodegradable Plastics from Renewable Sources. Flieger, M., y otros. 1, Praga : s.n., 2003, Folia Microbiol, Vol. 48, págs. 27-44.
7. Biodegradability and Mechanical Properties of Poly(vinyl alcohol)-Based Blend Plastics Through extrusion Method. Kopčilová, Martina, y otros. 2012, J Polym Environ, Vol. 21, págs. 88-94.
8. Introduction of Environmentally Degradable Parameters. Guo, Wenbin, y otros. 5, Tianjin : s.n., 2012, Vol. 7.
9. Properties of Starch Blends with Biodegradable Polymers. Wang, Xin-Li, Yang, Ke-Ke y Wang, Yu-Zhong. 3, Chengdu, China : s.n., 2003, Journal of Macromolecular Sciencie, Vol. C43, págs. 385-409.
10. Chemical syntheses of biodegradable polymers. 1, Aichi, Japan : s.n., 2002, Progress in Polymer Science, Vol. 27, págs. 87-133.
11. Eurpean Bioplastics. http://en.european-bioplastics.org/market/market-development/market-data-methodology/. [En línea]
12. Biodegradable Multiphase Systems Based on. Avérous, Luc. 3, Strasbourg, France : s.n., 2004, JOURNAL OF MACROMOLECULAR SCIENCE, Vol. C44, págs. 231-274.
13. Natural fiber-reinforced thermoplastic starch composites obtained by melt processing. Gironès, J., y otros. 2012, Composites Science and Technology, Vol. 72, págs. 858-863.
14. Laycock, Bronwyn G. y Halley, Peter J. Starch Applications: State of Market and New Trends. [ed.] P. Halley y Luc Averous. Starch Polymers From Genetic Engineering to Green Applications. Queensland, Australia : Elsevier, 2014, 14, págs. 381-419. DOI: 10.1016/B978-0-444-53730-0.00026-9.
15. Effects of plasticizers on the structure and properties of starch–clay. Tang, Xiaozhi, Alavi, Sajid y Herald, Thomas. [ed.] J.F. Kennedy y J.R. Mitchell. 3, Manhattan : s.n., April de 2008, Carbohydrate Polymers, Vol. 74, págs. 552-558. doi:10.1016/j.carbpol.2008.04.022.
16. Xu, Xuan, Visser, Richard G.F. y Trindale, Luisa M. Starch Modification by Biotechnology: State of Art and Perspectives. [ed.] Peter Halley y Luc Avérous. Starch Polymers from genetic engineering to green applications. s.l. : Newnes, 2014, 4, págs. 79-102.
17. Preparation and Properties of Plasticized Starch/Multiwalled Carbon Nanotubes Composites. Cao, Xiaodong, y otros. 2, July de 2007, Journal of Applied Polymer Sciencie, Vol. 106, págs. 1431-1437.
18. Various techniques for the modification of starch and the applications of its derivates. Neelman, Kavlani, Vijay, Sharma y Lalit, Singh. 5, Bareilly, India : s.n., may de 2012, International Research Journal of Pharmacy, Vol. 3.
19. Bioplastic: A Better Alternative For Sustainable Future. Marjadi, Darshan y Dharaiya, Nishith. 2, Gujarat, India : s.n., 2011, Vol. 2, págs. 159-163.
20. Visakh, P.M., y otros. Starch-Based bionanocomposites: processing and properties. [ed.] Habibi Youssef y Lucia Lucian. Polysaccharide Building Blocks: A Sustainable Approach to the Development of Renewable Biomaterials. s.l. : Wiley, 2012, 11, págs. 289-308. DOI: 10.1002/9781118229484.ch11.
21. Preparation and Characterization of Starch/PVA Blend for. Parvin, Fahmida, y otros. Dhaka, Bangladesh : Trans Tech Publications, Switzerland, 2010, Advanced Materials Research, Vols. 123-125, págs. 351-354.
22. A Review of Biodegradable Polymers:Uses, Current Developments in the Synthesis and Characterization of Biodegradable Polyesters, Blends of Biodegradable Polymers and Recent Advances in Biodegradation Studies. Amass, Wendy, Amass, Allan y Tighe, Brian. Birmingham, UK. : s.n., 1998, Polymer International, Vol. 47, págs. 89-144.
23. Biodegradable polymers as biomaterials. Nair, Lakshmi y Laurencin, Cato. Virginia, USA. : s.n., 2007, Progress in Polymer Science, Vol. 32, págs. 762-798.
24. Foaming of Synthetic and Natural Biodegradable Polymers. Marrazo, Carlo, Di Maio, Ernesto y Iannace, Salvatore. 2007, Journal of Cellular Plastics, Vol. 43, págs. 123-133.
25. Biodegradable Polymers. Zhang, Zheng, y otros. Piscataway, New Jersey : s.n.
26. Study of Bio-plastics As Green & Sustainable Alternative to Plastics. Laxmana Reddy, R., Sanjeevani Reddy, V. y Anusha Gupta, G. 5, Pradesh, India : s.n., 2013, International Journal of Emerging Technology and Advanced Engineering, Vol. 3, págs. 82-89.
27. Chemical modification of starch by reactive extrusion. Moad, Graeme. Clayton South, Australia : s.n., 2011, Progress in Polymer Science, Vol. 36, págs. 218-237. doi:10.1016/j.progpolymsci.2010.11.002.
28. Starch-based biodegradable blends: morphology and interface properties. Schwach, Emmanuelle y Avérous, Luc. Reims- Strasbourg, France : Society of Chemical Industry, 2004, Polymer International, Vol. 53, págs. 2115-2124. DOI: 10.1002/pi.1636.
29. Bioplásticos. Remar, Red de energía y Medio Ambiente. 2, Navarra, España : s.n., 2011.
30. Chemical syntheses of biodegradable polymers. Okada, Masahiko. Aichi, Japan : s.n., 2002, Progress in Polymer Science, Vol. 27, págs. 87-133.
31. New heat-resistant. Kazem, Mohammad, y otros. Pisa;Modena;Barcelona : s.n., 2013, Bioplastics Magazine, Vol. 8.
32. Preparation and characterization of ternary blends composed of polylactide, poly(E-caprolactone) and starch. Liao, Hsin-Tzu y Wu, Chin-San. 1-2, Taiwan, China : s.n., 2009, Materials Science and Engineering A, Vol. 515, págs. 207-214.
33. Synthesis, characterization and antibacterial activity of biodegradable starch/PVA composite films reinforced with cellulosic fibre. Priya, Bhanu, y otros. Pradesh, India : s.n., 2014, Carbohydrate Polymers, Vol. 109, págs. 171-179.
34. Properties of thermoplastic starch from cassava bagasse and cassava starch and their blends with poly (lactic acid). Teixeira, Eliangela de M., y otros. San Carlos, Brazil- Albany, USA : Elsevier, 2012, Industrial Crops and Products, Vol. 37, págs. 61-68. doi:10.1016/j.indcrop.2011.11.036.
35. Effects of relative humidity and ionic liquids on the water content and glass transition of plasticized starch. Bendaoud, Amine y Chalamet, Yvan. Saint-Etienne, France : s.n., 2013, Carbohydrate Polymers, Vol. 97, págs. 665-675. http://dx.doi.org/10.1016/j.carbpol.2013.05.060.
36. Byun, Youngjae, Zhang, Yachuan y Geng, Xin. Plasticization and Polymer Morphology. [ed.] Jung H. Han. Innovations in Food Packaging. 2. s.l. : Academic Press, 2014, 5, págs. 87-108. http://dx.doi.org/10.1016/B978-0-12-394601-0.00005-9.
37. Natural-based plasticizers and biopolymer films: A review. Adeodato Vieira, Melissa Gurgel, y otros. 3, Campinas : s.n., march de 2011, European Polymer Journal, Vol. 47, págs. 254-263. doi:10.1016/j.eurpolymj.2010.12.011.
38. Structure and properties of urea-plasticized starch films with different urea contents. Wang, Jia-li, Cheng, Fei y Zhu, Pu-xin. Chengdu, China : s.n., 30 de January de 2014, Carbohydrate Polymers, Vol. 101, págs. 1109-1115. http://dx.doi.org/10.1016/j.carbpol.2013.10.050.
39. Starch-based completely biodegradable polymer materials. Lu, D.R., Xiao, C.M. y Xu, S.J. 6, Quanzhou, China : s.n., 2009, eXPRESS Polymer Letters, Vol. 3, págs. 366-375. DOI: 10.3144/expresspolymlett.2009.46.
40. Product overview and market projection of emerging bio-based plastics. Shen, Li, Haufe, Juliane y Patel, Martin K. 4, June de 2009, Bioproducts and Biorefining,, págs. 25-40.
41. Biodegradation Studies of Polyvinyl Alcohol/Corn Starch Blend Films in Solid and Solution Media. Azahari, N. A., Othman, N. y Ismail, H. 2, Pulau Pinang,Malaysia : s.n., 2011, Journal of Physical Science, Vol. 22, págs. 15-31.
42. Effect of a Complex Plasticizer on the Structure and Properties of the Thermoplastic PVA/Starch Blends. Zhou, Xiang Yang, y otros. Guangzhou, China : s.n., 2009, Polymer-Plastics Technology and Engineering, Vol. 48, págs. 489-495. DOI: 10.1080/03602550902824275.
43. Preparation and characterization of thermoplastic starch/PLA blends by one-step reactive extrusion. Wang, Ning, Yu, Jiugao y Ma, Xiaofei. Tianjin, China : s.n., 2007, Polymer International, Vol. 56, págs. 1440-1447.
44. Synthesis and Properties of Reactive Interfacial Agents for Polycaprolactone-Starch Blends. Sugih, Asaf K., y otros. Groningen, The Netherlands : Wiley Periodicals, Inc., 2009, Journal ofAppliedPolymer Science, Vol. 114, págs. 2315-2326. DOI 10.1002/app.30712.
45. Biodegradation of poly(o-caprolactone)/starch blends and composites in composting and culture environments: the effect of compatibilization on the inherent biodegradability of the host polymer. Singh, R.P., y otros. 17, 2003, Carbohydrate Research, Vol. 33, págs. 1759-1769. DOI:10.1016/S0008-6215(03)00236-2.
46. Thermal properties and enzymatic degradation of blends of poly(3-caprolactone) with starches. Rosa, D.S., Lopes, D.R. y Calil, M.R. 6, Itatiba, Brazil : s.n., 2005, Vol. 4, págs. 756-761. DOI:10.1016/j.polymertesting.2005.03.014.
47. Properties of thermoplastic blends: starch–polycaprolactone. Avérous, L., y otros. 11, 2000, Polymer, Vol. 41, págs. 4157-4167.
48. Characterization of polyhydroxybutyrate-hydroxyvalerate (PHB-HV)/maize starch blend films. Reis, K.C., y otros. 4, 2008, Journal of Food Engineering, Vol. 89, págs. 361-369.
49. Current progress on bio-based polymers and their future trends. Babu, Ramesh P, O’Connor, Kevin y Seeram, Ramakrishna. 8, 2013, Progress in Biomaterials, Vol. 2. http://www.progressbiomaterials.com/content/2/1/8.
50. Mechanical and Thermal Properties of Hybrid Blends of LLDPE/Starch/PVA. Rahmah, M., Farhan, M. y Akidah, N.M.Y. 8, 2013, International Journal of Chemical, Nuclear, Metallurgical and Materials Engineering, Vol. 7, págs. 292-296.
51. Syntheses of PVA/Starch grafted hydrogels by iradiation. Zhai, Maolin, y otros. Beijing : s.n., 2002, Carbohydrate Polymers, Vol. 50, págs. 295-303.
52. Controlled preparation of physical cross-linked starch-g-PVA hydrogel. Xiao, Congming y Yang, Meiling. Quanzhou : s.n., 2006, Vol. 64, págs. 37-40. DOI:10.1016/j.carbpol.2005.10.020.
53. Properties of starch based blends. Part 2. Influence of poly vinyl alcohol addition and photocrosslinking on starch based materials mechanical properties. Follain, N., y otros.
54. Meré Marcos, Javier. Estudio del procesado de un polímero termoplástico basado en el almidón de patata amigable con el medio ambiente. Madrid, España : Unversidad Carlos III de Madrid , 2009.
55. Preparation of PHBV/Starch Blends by Reactive Blending and Their Characterization. Avella, M. y Errico, M.E. Arco Felice, Italy : s.n., 2000, Journal of Applied Polymer Science, Vol. 77, págs. 232-236.
56. Preparation and characterization of ultra violet (UV) radiation cured bio-degradable films of sago starch/PVA blend. Khan, Mubarak A., y otros. Dhaka, Bangladesh : s.n., 2006, Carbohydrate Polymers, Vol. 63, págs. 500-506. DOI:10.1016/j.carbpol.2005.10.019.
57. Surface properties of UV-irradiated poly(vinyl alcohol) films containing small amount of collagen. Sionkowska, Alina, y otros. Torun, Poland : s.n., 2009, Applied Surface Science, Vol. 225, págs. 4135-4139. DOI:10.1016/j.apsusc.2008.10.108.
58. Wittaya, Thawien. Rice Starch-Based Biodegradable Films: Properties Enhancement . [ed.] Ayman Amer Eissa. Structure and Function of Food Engineering. 2012, 5.
59. Modification of bean starch by g-irradiation: Effect on functional and morphological properties. Gani, Adil, y otros. Kashmir, India : s.n., 2012, LWT – Food Science and Technology, Vol. 49, págs. 162-169. DOI:10.1016/j.lwt.2012.04.028.
60. Vilpoux, Olivier y Avérous, Luc. Starch- Based plastics. Technology, use and potencialities of Latin American starchy tubers. 2004, Vol. 3, 18, págs. 521-553.
61. Mechanical Properties of Poly(e-caprolactone) and Poly(lactic acid) Blends. Simoes, C. L., Viana, J. C. y Cunha, A. M. Guimaraes, Portugal : s.n., 2009, Journal of Applied Polymer Science, Vol. 112, págs. 345-352.
62. Electrically Conductive Bioplastics from Cassava Starch. Arrieta, Alvaro A., y otros. 6, Córdoba- Medellín , Colombia : s.n., 2011, J. Braz. Chem. Soc., Vol. 22, págs. 1170-1176.
63. Tensile and water barrier properties of cassava starch composite films reinforced by synthetic zeolite and beidellite. Belibi, Pierre C., y otros. Yaoundé, Cameroon : s.n., 2013, Journal of Food Engineering, Vol. 115, págs. 339-346.
64. Physicochemical properties of starch–CMC–nanoclay biodegradable films. Almasi, Hadi, Ghanbarzadeh, Badak y Entezami, Ali. Tabriz, Iran : s.n., 2010, International Journal of Biological Macromolecules, Vol. 46, págs. 1-5. DOI:10.1016/j.ijbiomac.2009.10.001.
65. Ahmed, Jasmin, y otros, [ed.]. Starch-Based Polymeric Materials and Nanocomposites: Chemistry, Processing, and Applications. s.l. : CRC Press, 2012. 978-1-4398-5116-6.
66. Starch-based nano-biocomposites. Xie, Fengwei, y otros. Brisbane, Australia : s.n., 2013, Progress in Polymer Science, Vol. 38, págs. 1590-1628.
67. Dufresne, Alain, Thomas, Sabu y Pothan, Laly, [ed.]. Biopolymer Nanocomposites: Processing, Properties, and Applications. s.l. : John Wiley & Sons, 2013. 978-1-118-21835-8.
2018-9-6-1536224838