Biodegradable Multiphase Systems Based on Plasticized Starch: A Review

Abstract

The aim of this review is to show the relationships between the structure, the process, and the properties of biodegradable multiphase systems based on plasticized starch (PLS), the so‐called “thermoplastic starch.” These mutiphase materials are obtained when associating association between plasticized starches and other biodegradable materials, such as biodegradable polyesters [polycaprolactone (PCL), polyhydroxyalkanoates (PHAs), polylactic acid (PLA), polyesteramide (PEA), aliphatic, and aromatic copolyesters], or agro‐materials (ligno‐cellulosic fiber, lignin etc.). Depending on materials (soft, rigid) and the plastic processing system used, various structures (blends, composites, multilayers) can be obtained. The compatibility problematic between these hetero‐materials is analyzed. These starchy products show some interesting properties and have some applications in different fields: packaging, sports, catering, agriculture and gardening, or hygiene.     

Correlation between mechanical adhesion and interfacial properties of starch/biodegradable polyester blends

Biopolymers are preferred ingredients for the manufacture of materials because they are based on abundantly available and renewable raw materials that have benign environmental problems associated with their production, fabrication, use, and disposal; however, the wide use of biopolymers in engineering applications has not been achieved, mainly because of the inferior quality of many biopolymer‐based products. To overcome this limitation, studies have been initiated on blends of biopolymers and biodegradable synthetic polymers. We used the contact angle of probe liquids to measure the surface energy of polystyrene, the biodegradable polyesters polycaprolactone, poly(hydroxybutyrate‐co‐hydroxyvalerate), polylactic acid, polybutylene adipate terephthalate, and adipic poly(hydroxy ester ether), and normal starch. The surface energies were used to estimate the starch/polymer interfacial energy and work of adhesion. The calculated starch/polyester work of adhesion showed mixed correlation with published starch/polyester mechanical properties, indicating that factors other than interfacial properties might be dominant in determining the mechanical properties of some starch/polyester blends. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 920–930, 2001     

Solid-state NMR study of biodegradable starch/polycaprolactone blends

Abundant literature exists on starch or modified starch blended with biodegradable polyesters to achieve good performance with cheap compost plastics. The level of miscibility in these blends is one of the most relevant parameters. In the present study, solid-state ¹H and ¹³C NMR spectra, as well as carbon spin-lattice relaxation times T₁(C) and proton spin-lattice relaxation times T₁(H) and proton spin-lattice relaxation times in the rotating frame T_1ρ(H) of biodegradable starch (or starch formate)/polycaprolactone (PCL) (or polyester (PE) oligomers) blends and samples of the neat components were measured. From the T_1ρ(H) and T₁(H) relaxation times it follows that blends starch/PCL, starch/PE-oligomers and starch formate/PE-oligomers are phase separated even on the scale of 20-110 nm. On the contrary starch formate/PCL blend is phase separated on the scale 2.5-12 nm but homogeneously mixed on the scale 20-90 nm. Moreover, shorter T₁(C) and especially T_1ρ(H) values found for the starch or starch formate component in all these blends in comparison with neat samples show that molecular mobility of starch and starch formate segments is affected by blending. This indicates some miscibility also in phase separated blends which can happen in amorphous channels of starch.     

Biodegradable materials by reactive extrusion: from catalyzed polymerization to functionalization and blend compatibilization

This contribution aims at reviewing how reactive extrusion (REx) technique can participate in the design and development of biodegradable polymeric materials more particularly based on aliphatic polyesters issued from both renewable (agrochemical) and fossil (petrochemical) resources. On one side, REx will be approached for producing in a continuous way biodegradable aliphatic polyesters by ring-opening polymerization of lactones. Tin and aluminum-based catalysts will be considered for quantitatively converting the cyclic monomer in high molecular weight polyester chains within residence time of a few minutes only. On the other hand, such polyesters will undergo various chemical modifications again performed by REx. Self-branching reactions will be investigated in order to compensate the characteristic molecular weight reduction of the polyester chains as triggered by hydrolysis and/or transesterification side-reactions. Controlled functionalization reactions by maleic anhydride treatment will be studied as well. Finally biodegradable composite materials will be produced by REx and will rely upon the interface compatibilization between the polyester matrix and natural fillers such as starch granules or talc microparticles. To cite this article: J.-M. Raquez, et al., C. R. Chimie 9 (2006).     

Hydrophobic modification of starch via grafting with an oxazoline-derivative

The application of starch in tailored materials is limited because of the high hydrophilicity of the polysaccharide. Thus, simple and efficient paths for the hydrophobic modification of native, cationic or thermoplastic starches by means of a radical grafting process using bifunctional fatty acid oxazoline derivatives were investigated. The modified starches can be manufactured by means of an extrusion process showing high grafting yields at adjustable grafting contents from 2.5 to 30%. Resulting starch materials are distinguished by modified water absorption properties and solubility, which is a prerequisite for their application in the paper or painting industry. Moreover the structure of the oxazoline derivative supplies the opportunity for reactive blending of different polymers carrying carboxyl, amino, mercapto or epoxy groups. This is exemplarily shown for the conversion with biodegradable polyesters, which contain carboxylic acid functions. Film forming properties of the new starch-based materials were studied. Results of the examination of manufactured shouldered test bars of starches coupled with biodegradable polyesters are presented as well.     

Effect of soy protein isolate on the thermal, mechanical and morphological properties of poly (-caprolactone) and corn starch blends

The development of biodegradable polymers is considered to be a good alternative to decrease the volume of the plastic waste disposed into the environment every year. The use of natural polymers as raw materials to develop polymer blends and composites has increased the demand for renewable sources such as starch and soy protein.In this work, the authors prepared and characterized the thermal, mechanical and morphological properties of blends based on poly (-caprolactone) and modified corn starch, with added soy protein isolate (SPI) and sorbitol. All samples were processed by extrusion in a single-screw extruder and hot pressing. It was observed that the addition of modified corn starch and SPI were responsible for the reduction of thermal and mechanical properties of the materials, compared to pristine PCL. However, with increasing amounts of SPI and the reduction of starch incorporated into the samples, their properties tend to recover. The insertion of soy protein isolate in the formulations was done with the aim of balancing the C/N ratio of the blend, which plays a key role in the biodegradation process of these materials.     

淀粉基高分子材料的研究进展

概述了近5年国内外在淀粉的化学、物理改性及其作为一种材料使用方面取得的最新研究进展.淀粉的化学改性主要介绍了淀粉的酯化、醚化、氧化、交联、接枝共聚等,而物理改性主要介绍了淀粉分别与黏土、脂肪族聚酯、聚乙烯醇以及纤维素等天然大分子的共混改性,同时还介绍了通过酸化制备淀粉纳米晶.淀粉基材料除了用于制备可生物降解塑料、吸附材...     

Mechanical and thermal properties of poly(3-hydroxybutyrate) blends with starch and starch derivatives

Poly(3-hydroxybutyrate) (PHB) is a highly crystalline, biodegradable and biocompatible thermoplastic. However, its limited utilization as a commodity plastic is associated to both high cost and very poor mechanical properties. Blending PHB with a natural polymer, such as starch, is one way to improve its properties and to get low price raw materials, though they are not miscible since there are no strong interactions between the hydrophilic starch and the hydrophobic PHB. In this study binary blends of PHB were prepared with natural starch, starch-adipate and grafted starch-urethane derivatives. The PHB blends were characterized in terms of their mechanical and thermal properties. For all blends a decrease of the Young modulus was observed as compared to the pure PHB. However, blends containing natural starches and starch adipate resulted in brittle materials. A significant decrease of both glass transition temperature (Tg) and melting point (Tm) was observed for all formulations. The best results, lower modulus and Tg were obtained with grafted starch-urethane blends using poly(propylene glycol).     

Thermal degradation of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) and their blends upon melt processing

Poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) are biodegradable aliphatic polyesters, which being semicrystalline and thermoplastic can be processed by conventional methods. Their blends give interesting materials for industrial packaging applications, due to their increased ductility as PBAT content increases. However, like many aliphatic polyesters, the PLA matrix degrades upon melt processing thus affecting the thermo-mechanical features of the blended material. In this work, we studied the effect of processing at high temperature on the molecular weight distribution, morphology, and thermo-mechanical properties of both homopolymers, as well as the PLA/PBAT 75/25 blend. Notably, different processing conditions were adopted in terms of temperature (range 150-200 °C) and other relevant processing parameters (moisture removal and nitrogen atmosphere). Analysis of PLA/PBAT blends indicated that intermolecular chain reactions took place under strong degradative conditions of PLA, yielding PLA/PBAT mixed chains (copolymers). Increasing amounts of copolymers resulted in improved phase dispersion and increased ductility, as SEM and mechanical tests indicated. Conversely, reduced PLA degradation with less copolymer formation, afforded higher modulus materials, owing to poorer dispersion of the soft phase (PBAT) into the PLA matrix.     

Comparison of glass transition and interpretation on miscibility in blends of amorphous poly(vinyl methyl ether) with highly crystallizable versus less‐crystallizable polyesters

Various phase behavior of blends of poly(vinyl ether)s with polyesters of two types (highly crystalline and less crystalline with different main‐chains) were examined using differential scanning calorimetry (DSC) and optical microscopy (OM). Effects of varying the main‐chain polarity of the constituent polyesters on the phase behavior of the blends were analyzed. Miscibility in PVME/polyester blends was found only in polyesters with backbone CH₂/CO ratio = 3.5 to 7.0). T_g‐composition relationships for blends of PVME with highly crystalline polyesters (PBA, PHS) were found to differ significantly from those for PVME blends with less‐crystalline polyesters (PTA, PEAz). Crystallinity of highly crystalline polyester constituents in blends caused significant asymmetry in the T_g‐composition relationships, and induced positive deviation of blends' T_g above linearity; on the other hand, blends of PVME with less crystalline polyesters exhibit typical Fox or Gordon‐Taylor types of relationships. The χ parameters for the miscible blends were found to range from ?0.17 to ?0.33, reflecting generally weak interactions. Phase behavior was analyzed and compared among blends of PVME with rapidly crystallizing vs. less‐crystallizing polyesters, respectively. Effects of polyesters' crystallinity and structures on phase behavior of PVME/polyester blends are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2899–2911, 2007     

Biodegradable materials — Present situation and future perspectives

Biodegradable polymers constitute a loosely defined family of polymers that are designed to degrade through the action of living organisms. They offer a possible alternative to traditional nonbiodegradable polymers if recycling is impractical or not economical. The main driving force behind this technology is the solid waste problem, particularly with regard to the decreasing availability of landfills, the litter problem and the pollution of marine environment by non-biodegradable plastics. Technologies like composting used for the disposal of food and yard waste are the most suitable for the disposal of biodegradable materials. European Standardisation Committee (CEN), Organic Reclamation and Composting Association (ORCA) and German Institute for Standardisation (DIN) have already defined, at a draft level, the basic requirements for a product to be declared compostable. They are based on: complete biodegradability of the product in a time period compatible with composting, measured through respirometric tests (ASTM D5338-9, ISO/CD14855, etc); disintegration of the material during the fermentation phase; no negative effects on compost quality; checking of laboratory-scale results on pilot/full-scale composting plants. These requirements set forth a common base for a universal marking system to readily identify products to be composted. Thermoplastic starch-based polymers and aliphatic polyesters are the two classes of biodegradable materials with the greatest near-term potential. This paper reviews a great variety of properties, structures and biodegradation behaviour of thermoplastic starch in combination with poly(vinyl alcohol) or some aliphatic polyesters like poly(hydroxybutyrate-co-hydroxyvalerate), poly(lactic acid), poly(ϵ-caprolactone) and poly(butanediyl succinate).     

Degradation and recovery in poly(butylene adipate-co-terephthalate)/ thermoplastic starch blends

The economic and social impact of the increasing waste disposal problems of conventional plastic materials are well known and promoted the search for better recyclable and biodegradable polymers, blends and compounds. Fully biodegradable blends of poly(butylene adipate-co-terephthalate) (PBAT), a synthetic copolyester, and thermoplastic starch (TPS), a natural polysaccharide, are of technical and economic interest in the quest for eco-friendly polymeric materials to substitute conventional alternatives. One of less desirable characteristics of many new biodegradable materials is their relative thermal instability (degradation) under processing conditions.In the present work, PBAT/TPS blends with up to 30% TPS were processed at different temperatures in a laboratory internal mixer, with and without the incorporation of a chain extender additive (Joncryl). The rate of change of torque during the melt processing stage, adjusted to eliminate minor temperature variations, is a very sensitive indicator of variation of molar mass due to degradation and recovery. It was found that TPS content promotes thermal degradation in the PBAT/TPS blends at levels above those observed in neat components, in a strongly composition and temperature-dependent process. The addition of 1% of the chain extender additive partially reverts the process, especially during processing at high temperature.     

Biodegradable compositions by reactive processing of aliphatic polyester/polysaccharide blends

Commercially available biodegradable aliphatic polyesters, i.e., high molecular weight poly(ϵ-caprolactone) (PCL) and polylactide (PLA), were melt blended with a well-known natural and biodegradable polysaccharide: starch either as corn starch granules or as thermoplastic corn starch after plasticization with glycerol. Conventional melt blending yielded compositions with poor mechanical performances as a result of lack of interfacial adhesion between the rather hydrophobic polyester matrix and the highly hydrophilic and moisture sensitive starch phase. Interface compatibilization was achieved via two different strategies depending on the nature of the polyester chains. In case of PLA/starch compositions, PLA chains were grafted with maleic anhydride through a free radical reaction conducted by reactive extrusion. The maleic anhydride-grafted PLA chains (MAG-PLA) allowed for reinforcing the interfacial adhesion with granular starch as attested by TEM of cryofracture surface. As far as PCL/starch blends were concerned, the compatibilization was achieved via the interfacial localization of amphiphilic graft copolymers formed by grafting of PCL chains onto a polysaccharide backbone such as dextran. The PCL-grafted polysaccharide copolymers were synthesized by controlled ring-opening polymerization of ϵ-caprolactone proceeding via a coordination-insertion mechanism. These compatibilized PCL/starch compositions displayed much improved mechanical properties as determined by tensile testing as well as a much more rapid biodegradation as measured by composting testing.     

Influence of various starch types on PCL/starch blends anaerobic biodegradation

Research concentrated on the biodegradable capability of PCL blends with various types of starch in an anaerobic aqueous environment of mesophilic sludge from a municipal wastewater treatment plant. For blend preparation, use was made of a native starch Meritena from maize, another from Waxy – a genetically modified type of maize, as well as Gel Instant, a gelatinized starch, and an amaranth starch. Additional PCL/starch blends were prepared from the same starch types, but these were initially plasticized with glycerol. The biodegradability tests were supplemented with thermo gravimetric analysis (TGA), and differential scanning calorimetry (DSC); morphology was identified using scanning electron microscopy (SEM), plus mechanical properties were also tested. While mixtures of PCL with starches plasticized with glycerol exhibited improved mechanical properties and a higher degree of biodegradation in the anaerobic environment, mixtures of PCL with pure forms of starch were ascertained as rather resistant to the anaerobic aqueous environment. TGA and DSC analysis confirmed the removal of starch and glycerol from the PCL matrix. SEM then proved these results through the absence of starch grains in the samples following anaerobic biodegradation.     

热塑性淀粉/PBS共混物的微生物降解性研究

以甘油作为增塑剂,采用玉米淀粉与改性后的聚丁二酸丁二醇酯(PBS)熔融共混制备出淀粉/PBS共混材料.对这种改善了两相相容性的共混材料在特定微生物条件下的降解行为进行了研究.结果显示,共混物降解28天后,含有30%PBS的共混物质量损失达到35%左右,其力学性能只有降解前的20%,甘油含量减小和PBS含量增加均能减缓材料的降解.且随着降解时间的延长,PBS的结晶度和熔点有所提高.     

淀粉/聚酯体系生物可降解材料

主要从淀粉／聚酯共混、聚酯—淀粉—聚酯复合层、交联及生物降解性方面综述了近年来淀粉/聚酯体系的生物可降解材料的研究进展。     

Blends of different linear polyamides with hyperbranched aromatic AB2 and A2 + B3 polyesters

To explore the possible applications of hyperbranched polymers for modifying linear polyamides, two hyperbranched aromatic polyesters characterized as high T_g polymers possessing phenolic end groups were used in melt mixing with partly aromatic polyamide and commercially available aliphatic polyamide‐6, respectively. Different amounts of both hyperbranched polyesters (from 1 wt % up to 20 wt %) were added to the polyamides, and the influence of these hyperbranched polyesters on the properties of the polyamides was investigated. The hyperbranched polyester based on an AB₂ approach was found to be the most effective modifier. A significant increase of the glass transition temperature of the final blend was detected. However, a remarkable reduction of crystallinity as well as complex melt viscosity of those blends was also observed. The use of an A₂+B₃ hyperbranched polyester as melt modifier for the polyamides was less effective for changing the thermal properties, and the complex melt viscosity of the final material increased since heterogeneous blends were formed. In contrast to that, generally, the addition of the AB₂ hyperbranched polyester to the polyamides resulted in homogeneous blends with improved T_g and processability. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3558–3572, 2009     

Synthesis,thermal, rheological characteristics,and enzymatic degradation of aliphatic polyesters with lignin‐based aromatic pendant groups

This research aims to produce lignin‐based biodegradable polyesters with improved thermal quality. A series of aliphatic polyesters with lignin‐based aromatic side groups were synthesized by conventional melt‐polycondensation. Decent molecular weight (21–64 kg mol^?1) was achieved for the polymerizations. The molecular structures and thermal and mechanical properties of the obtained polyesters were characterized. As a result, the obtained polyesters are all amorphous, and their glass‐transition temperature (T_g) depends on the size of the pendant aromatic group (31–51 °C). Furthermore, according to the TGA results, the thermal decomposition temperatures of the polyesters are all above 390 °C, which make them superior compared with commercial biodegradable polyesters like polylactic acid or polyhydroxyalkanoates. Finally, rheological characteristics and enzymatic degradation of the obtained polyesters were also measured. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2314–2323     

Genetically Modified Starch as an Industrial Raw Material

Abstract

Starch is an important raw material for industrial applications, both for food and nonfood purposes. Of particular interest is the use of starch as a nonpetroleum chemical stock for the manufacture of biodegradable polymers. Annual EC starch production is nearing 10 million tons, with 80% from cereals and 20% from potatoes, and grows at 4?5% annually. The potential for genetically modified starch is considered very high. Such starch offers significant advantages: 1) chemical modifications, which are expensive and environmentally hazardous, are replaced; 2) novel carbohydrates can be produced.     

New Strategy for Controlling Biodegradability of Biodegradable Polyesters by Enzyme‐Catalyzed Surface Grafting

A novel preparation method for the core‐shell type biodegradable polyesters or biodegradable materials grafted with biodegradable polyesters was developed by alkaline surface treatment of biodegradable polyester films and subsequent enzymatic polymerization of aliphatic lactones, one example of which is shown in this study, i.e., the preparation of poly(L ‐lactide) (PLLA) film grafted with poly(ε‐caprolactone). It is revealed that only alkaline surface treatment or the combination of alkaline surface treatment and enzyme‐catalyzed grafting, the former and the latter, respectively accelerating and delaying the enzymatic degradation of PLLA, will give PLLA materials having a wide variety of biodegradability. Also, the specificity of the enzyme used for hydrolysis could be used to confirm the grafted chain species.