Biodegradable Complex Polymers from Casein and Potato Starch

Potato starch was blended with defatted milk in proportions providing a 4:1, 3:1, 2:1, 1:1, 1,:2, 1:3, and 1:4 starch/casein ratio. Precipitation was achieved by addition of either hydrochloric acid or leaven. Composition of precipitated products was determined based on elemental analysis for nitrogen. Generally, differences between attempted and achieved casein-to-starch proportions did not exceed 10%. Products coprecipitated with hydrochloric acid were slightly richer in casein than products obtained with leaven. Aqueous solubility, water binding capacity, IR spectra, and thermal analysis (thermogravimetry, TG, and differential thermogravimetry, DTG) were recorded for the precipitates. Analyses revealed that the precipitates were not simple physical mixtures of the components. Partial insolubility in 7 M aqueous urea showed that casein and potato starch are chemically bound. Comparison of the spectra and thermograms suggested that complexes of the 1:1 composition were formed constituting a nucleus of the aggregates carrying excessive amounts of either starch or casein.     

Reactive Blending of Biodegradable Polymers: PLA and Starch

Poly(lactic acid) (PLA) and starch are important biodegradable polymers. Mechanical properties of blends of PLA and starch using conventional processes were very poor because of incompatibility. In this study, PLA and starch were blended with a reactive agent during the extrusion process. The affects of the reactive blending were investigated and significant improvements were confirmed by measuring the tensile strength and elongation at break, IR spectra, and DSC.     

Structural Differences Between Lignin Model Polymers Synthesized from Various Monomers

In a plant cell wall, lignin is synthesized from several monomeric precursors, combined in various ratios. The variation in monomer type and quantity enables multifunctional role of lignin in plants. Thus, it is important to know how different combinations of lignin monomers impact variability of bond types and local structural changes in the polymer. Lignin model polymers are a good model system for studies of relation between variations of the starting monomers and structural variations within the polymer. We synthesized lignin model polymers from three monomers, CF??based on coniferyl alcohol and ferulic acid in monomer proportions 5:1 and 10:1 (w/w), CP??based on coniferyl alcohol and p-coumaric acid in proportion 10:1 (w/w) and CA??based on pure coniferyl alcohol. We studied structural modifications in the obtained polymers, by combining fluorescence microscopy and spectroscopy, FT-IR and Raman spectroscopy, in parallel with determination of polymers?? molecular mass distribution. The differences in the low M _w region of the distribution curves of the 10:1 polymers in comparison with the CA polymer may be connected with the increased content of C=C bonds and decreased content of condensed structures, as observed in FT-IR spectra and indicated by the analysis of fluorescence spectra. The 5:1 CF polymer contains a different type of structure in comparison with the 10:1 CF polymers, reflected in its simpler M _w distribution, higher homogeneity of the fluorescence emitting structures and in the appearance of a new high-wavelength emission component. We propose that this component may originate from ??-conjugated chains, which are longer in this polymer. The results are a contribution to the understanding of the involvement of structural variations of lignin polymers in the cell wall structural plasticity.     

Biodegradable Polymers from 5-Hydroxylevulinic Acid: 1. Synthesis and Characterization of Poly(5-hydroxylevulinic acid)

As an attempt to synthesize new biodegradable polymers from renewable cellulose resources, melt polycondensation of 5-hydroxylevulinic acid (5-HLA) was reported for the first time. The resulting product, poly(5-hydroxylevulinic acid) (PHLA), was synthesized and characterized with GPC, FTIR, ¹H NMR and DSC. The in vitro degradation behaviors in phosphate-buffered saline (PBS) and in deionized water (DW) were also examined. The molecular weight of PHLA is not high (several 1,000s), but it possesses unordinary high glass transition temperature (as high as 120 °C). This is very different from existing aliphatic polyesters that usually have T _gs lower than 60 °C. The high T _g is attributed to the formation of inter- and/or intramolecular hydrogen bonds due to a characteristic keto–enol tautomerism equilibrium in the polymer structure. PHLA readily degraded hydrolytically in aqueous media.     

Biodegradable Poly(butylene succinate) and Poly(butylene adipate-co-terephthalate) Blends: Reactive Extrusion and Performance Evaluation

Two biodegradable polyesters, poly(butylene adipate-co-terephthalate) (PBAT) and poly(butylene succinate) (PBS) were melt-compounded in a twin screw extruder to fabricate a novel PBS/PBAT blend. The compatibility of the blend was attributed to the transesterification reaction that was confirmed by Fourier transform infrared spectroscopy. The Gibbs free energy equation was applied to explain the miscibility of the resulting blend. Dynamic mechanical analysis of the blends exhibits an intermediate tanδ peak compared to the individual components which suggests that the blend achieved compatibility. One of the key findings is that the tensile strength of the optimized blend is higher than each of the blended partner. Rheological properties revealed a strong shear-thinning tendency of the blend by the addition of PBAT into PBS. The phase morphology of the blends was observed through scanning electron microscopy, which revealed that phase separation occurred in the blends. The spherulite growth in the blends was highly influenced by the crystallization temperature and composition. In addition, the presence of a dispersed amorphous phase was found to be a hindrance to the spherulite growth, which was confirmed by polarizing optical microscopy. Furthermore, the increased crystallization ability of PBAT in the blend systems gives the blend a balanced thermal resistance property.     

Renewable Resources and Enzymatic Processes to Create Functional Polymers: Adapting Materials and Reactions from Food Processing

We are exploiting materials and concepts from food science to create functionalized, environmentally friendly derivatives of the biopolymer chitosan, a byproduct of seafood processing. Functional groups are grafted onto chitosan using tyrosinase, the enzyme responsible for food browning. The functionalizing groups studied include low-molecular-weight phenols derived from natural sources and high-molecular-weight proteins. The approach of using low-molecular-weight phenols to functionalize chitosan is illustrated with arbutin, a natural phenol found in pears. Results demonstrate that tyrosinase initiates reactions that lead to the conversion of arbutin–chitosan solutions into gels. These gels can be rapidly broken by treatment with the chitosan-hydrolyzing enzyme chitosanase, demonstrating that the chitosan derivatives remain biodegradable. We briefly review other studies in which low-molecular-weight natural phenols are enzymatically grafted onto chitosan to confer functional properties. The creation of co-polymers is illustrated by results in which tyrosinase is used to couple gelatin onto chitosan. Gelatin is a proteinaceous byproduct of meat production. The tyrosinase-generated gelatin–chitosan conjugates have been observed to offer interesting rheological and thermal properties. These results demonstrate the potential for using renewable resources and enzymatic processing to create environmentally friendly polymers with useful functional properties.     

Rheological Behavior Under Shear and Non-Isothermal Elongational Flow of Biodegradable Polymers for Foam Extrusion

The production of many items, in particular for food packaging applications, is based on foam extrusion and thermoforming. These operations require the use of polymers which can grant some specific rheological properties, both under shear and elongational flow. In this work, the behavior of some biodegradable polymers [Mater-Bi^® and poly(lactic acid)] under shear and non-isothermal elongational flow was investigated and compared with a traditional, non-biodegradable polymer, in order to assess their suitability for industrial-scale foam extrusion and thermoforming. The rheological characterization evidenced the differences between the different biodegradable polymers and the reference polystyrene (PS), as well as the effect of humidity on their main rheological properties. This can be of great interest in helping to find an optimum solution in replacing PS for the production of food packaging items.     

Mechanical Performance and Design Criteria of Biodegradable Low-tunnel Films

The overall mechanical behaviour of a series of experimental Mater-Bi made thin low-tunnel films is analysed with respect to the effect of two major factors: the film processing optimisation during manufacturing and the design of the low-tunnels structural system. The analysis of the mechanical behaviour of the biodegradable low-tunnel films, based on the results of extensive full-scale and small-scale experiments, combined with laboratory testing of the mechanical properties of the film, proves that a rather good mechanical behaviour is possible for these films, comparable to the behaviour of conventional agricultural films in terms of strength, provided that two criteria are met: (a) the low tunnel structural design is based on the initial stress at yield value of the film, which represents the asymptotic value of the tensile strength of the film, following its evolution with the time of exposure to real field conditions; (b) the processing of the film is optimised for the particular biodegradable material and film thickness under consideration. It is also confirmed that the stabilisation schemes used with conventional polyethylene films are not suitable for the biodegradable films.

Degradation Behaviour and Field Performance of Experimental Biodegradable Drip Irrigation Systems

The field performance of experimental biodegradable drip irrigation thin wall and regular pipes was investigated through three sets of full-scale experiments and in the laboratory. These experimental biodegradable drip irrigation systems were produced through the processing of biodegradable under real soil conditions polymers, Mater-Bi and Bioflex. The mechanical behaviour of the biodegradable thin wall pipes during the irrigation period was more unstable when compared to the corresponding behaviour of the rigid pipes. The tensile strength of the Mater-Bi and Bioflex thin wall pipes remained almost constant during the total exposure time, except from the folding areas. During the first 7–23 days of exposure in the field, the thin wall pipes had already lost more than the 50% of their initial elongation at break value due to degradation. However, their hydraulic performance began to decline only after a period of 100–120 days with the simultaneous formation of the first cracks. Likewise, the majority of the series of biodegradable rigid pipes exhibited a remarkable reduction in their elongation at break values in the transverse direction within the first 2 weeks. Despite the significant drop of the elongation at break, all biodegradable rigid pipes generally retained their tensile strength as well as a satisfactory hydraulic performance during almost the whole duration of their exposure. A few premature leakages in some points adjoining the drippers were observed after 8–10 weeks of exposure.     

Performance and Environmental Impact of Biodegradable Films in Agriculture: A Field Study on Protected Cultivation

The performance, the degradability in soil and the environmental impact of biodegradable starch-based soil mulching and low tunnel films were assessed by means of field and laboratory tests. The lifetime of the biodegradable mulches was 9 months and of the biodegradable low-tunnel films 6 months. The radiometric properties of the biodegradable films influenced positively the microclimate: air temperature under the biodegradable low tunnel films was 2 °C higher than under the low density polyethylene films, resulting in an up to 20% higher yield of strawberries. At the end of the cultivation period, the biodegradable mulches were broken up and buried in the field soil together with the plant residues. One year after burial, less than 4% of the initial weight of the biodegradable film was found in the soil. According to ecotoxicity tests, the kinetic luminescent bacteria test with Vibrio fischeri and the Enchytraeus albidus ISO/CD 16387 reproduction potential, there was no evidence of ecotoxicity in the soil during the biodegradation process. Furthermore, there was no change in the diversity of ammonia-oxidizing bacteria in the soil determined on the basis of the appearance of amoA gene diversity in denaturing gradient gel electrophoresis.     

Processing and Characterization of Short-Fiber Reinforced Jute/Poly Butylene Succinate Biodegradable Composites: The Effect of Weld-Line

Fabrication of complex injection molded parts often involves the use of multiple gates. In such situations, polymer melts from different gates meld to form the molded part (weld line). This paper reports on the fabrication and characterization of the mechanical and morphological properties of short fiber reinforced jute/poly butylene succinate (PBS) biodegradable composites. The effect of a dual gated mold in the fabrication of welded specimens was a key focus of the investigation. It was observed that incorporation of jute fiber (10 wt%) conferred drastic changes on the stress–strain properties of the matrix as the elongation at break (EB), dropped from 160% in the matrix to just 10% in the composite. The tensile strength of the composite was lower than that of the matrix. However, it is noteworthy that the tensile modulus of the composite increased. Bending test also revealed that both bending strength and modulus increased with the incorporation of jute. Morphological studies of the tensile fracture surface using SEM revealed two types of failure mode. Ductile failure was indicated by plastic deformation at the initiation of fracture followed by brittle failure. The good interfacial bonding indicated between jute and PBS was attributed to positive interaction between the two polar polymers. A comparison of the non-weld and weld-line samples revealed that the weld-line composites have better mechanical integrity than the corresponding polymer matrix with weld line. The results also revealed that elongation at break and toughness are most sensitive to the presence of the weld-line whereas flexural properties are least sensitive.     

Melt Processing of a New Biodegradable Synthetic Polymer in High-Speed Spinning and Underpressure Spunbonding Process

A new biodegradable synthetic polyesteramid (PEA) was characterized by means of thermogravimetry (TG) differential scanning calorimetry (DSC) and dynamic rheological measurements. Two glass transition ranges at about –33 and 38°C and a melting enthalpy of 33 J/g were measured, indicating that PEA is an immiscible blend of two components with a small crystalline part. The material was spun in a high-speed spinning process within the range of 2,000–6,000 M/min and an underpressure spunbonding process within the range of 3,600–7,700 M/min. The textile physical properties of the fibers were 100 MPa tenacity at an elongation at break of 30%, and an E-modulus of 0.5 GPa. The mass per unit area of the spunbonded nonwovens ranged from 70–159 g/M ². The strength of the spunbonded nonwovens was 28–51 N and 42–74 N in machine and cross direction, respectively. The air permeability of the nonwovens decreased at high air velocities and more fineness of the filaments from 1240–380 l/M ² s.     

Biodegradable Soy-Based Plastics: Opportunities and Challenges

Today's plastics are designed with little consideration for their ultimate disposability or the effect of the resources (feedstocks) used in making them. This has resulted in mounting worldwide concerns over the environmental consequences of such materials when they enter the mainstream after their intended uses. This led to the concept of designing and engineering new biodegradable materials–materials that have the performance characteristics of today's materials but that undergo biodegradation along with other organic waste to soil humic materials. Hence, the production of biodegradable materials from annually renewable agricultural feedstocks has attracted attention in recent years. Agricultural materials such as starches and proteins are biodegradable and environmentally friendly. Soybean is a good candidate for manufacturing a large number of chemicals, including biodegradable plastics, as it is abundantly available and cheap. Soy protein concentrate, isolate, or flakes could be compounded with synthetic biodegradable plastics such as polycaprolactone or poly (lactic acid) to make molded products or edible films or shopping bags and make the environment cleaner and greener.     

Biodegradable/Bio-plastics: Myths and Realities

Journal of Polymers and the Environment - The plastics industry is proliferating continuously and the global plastics production in 2018 has reached around 360 million tones. This has further...     

Poly(Lactic Acid) Blended with Cellulolytic Enzyme Lignin: Mechanical and Thermal Properties and Morphology Evaluation

“Green”/bio-based blends of poly(lactic acid) (PLA) and cellulolytic enzyme lignin (CEL) were prepared by twin-screw extrusion blending. The mechanical and thermal properties and the morphology of the blends were investigated. It was found that the Young’s modulus of the PLA/CEL blends is significantly higher than that of the neat PLA and the Shore hardness is also somewhat improved. However, the tensile strength, the elongation at break, and the impact strength are slightly decreased. Thermogravimetric analysis (TGA) shows that the thermal stability of the PLA is not significantly affected by the incorporation of the CEL, even with 40 wt% CEL. The results of FT-IR and SEM reveal that the CEL and the PLA are miscible and there are efficient interactions at the interfaces between them. These findings show that the CEL is a kind of feasible filler for the PLA-based blends.     

Ecotoxicity Evaluation of the Biodegradable Polymers PLA,PBAT and its Blends Using <Emphasis Type="Italic">Allium cepa</Emphasis> as Test Organism

Biodegradable polymers are considered a feasible option to minimize the environment impacts of high disposal of solid waste. Nevertheless, environmental safety of these materials is a few explored issue. In this context, this study evaluated ecotoxicological effects in soil of the biodegradable materials poly(lactic acid)-PLA, poly(butylene adipate co-terephthalate)-PBAT and their blends compatibilized with a chain extender. The tool used for this analysis was the bioassay with Allium cepa as test organism. The studied materials were not phytotoxic, cytotoxic, genotoxic nor mutagenic for meristematic cells of A. cepa.     

Novel Pretreatment Performance Evaluation for Cellulose Nanofibrils Extraction from Ficus natalensis Barkcloth

Recently, nanosized cellulose materials extraction is extensively interesting from the sources of sustainable materials. Cellulose nanofibrils (CNF) extraction through green bio-based materials featured as promising interest in the field of science. In this study, dimethyl sulfoxide (DMSO) was applied to examine its effectiveness in pretreating the Ficus natalensis barkcloth cellulose (FNBC) for CNF production before 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO) oxidation. The pretreatment performance of DMSO was evaluated based on the structural and morphological changes. DMSO pretreated FNBC attained the most dramatic morphological changes as compared to untreated cellulose samples. The results of the scanning electron microscope (SEM) and transmission electron microscope (TEM) shows that there is an extensive structural disruption of FNBC during the pretreatment process, which could be because of outstanding ability to eliminate non-cellulosic materials and amorphous regions from the FNBC, confirmed by the X-ray diffractometry (XRD) showing higher crystallinity values, as well as higher thermal stabilities values of pretreated FNBC samples, were also noted. Overall, this study revealed a tremendously effective and pioneer pretreatment method for fractionating FNBC, to stimulate the successive extraction of cellulose nanofibrils. Furthermore, based on the cellulose and CNF characterizations, this study showed that F. natalensis barkcloth could be considered as an alternative source of cellulose for potential value-added industrial applications such as the food industry, paper making, and biomedicines.

Graphic Abstract

     

Novel Biodegradable Cast Film from Cherry Tree Gum,Development, Modification and Characterization

The feasibility of sweet cherry gum as a bio-based film-forming material and effect of hydrogen peroxide as a chemical modifier investigated. The influence of film compositions (gum, glycerol) and hydrogen peroxide on the physical properties of films, including solubility in water, permeability to water vapor (WVP), mechanical properties, and transparency, thermal and microstructural properties evaluated. The results showed that WVP and thickness increased by gum and glycerol concentration, but significantly decreased by hydrogen peroxide. As expected, elongation-at-break and solubility, increased at higher concentration of glycerol but the tensile strength decreased at the same condition. The film transparency was influenced by the dry weight content and was improved by higher concentrations of hydrogen peroxide. The partial degradation of polymer chain by hydrogen peroxide was observed by FTIR analysis.