Françoise Silvestre

Polymer biodegradation: Mechanisms and estimation techniques – A review

Within the frame of the sustainable development, new materials are being conceived in order to increase their biodegradability properties. Biodegradation is considered to take place throughout three stages: biodeterioration, biofragmentation and assimilation, without neglect the participation of abiotic factors. However, most of the techniques used by researchers in this area are inadequate to provide evidence of the final stage: assimilation. In this review, we describe the different stages of biodegradation and we state several techniques used by some authors working in this domain. Validate assimilation (including mineralisation) is an important aspect to guarantee the real biodegradability of items of consumption (in particular friendly environmental new materials). The aim of this review is to emphasise the importance of measure as well as possible, the last stage of the biodegradation, in order to certify the integration of new materials into the biogeochemical cycles. Finally, we give a perspective to use the natural labelling of stable isotopes in the environment, by means of a new methodology based on the isotopic fractionation to validate assimilation by microorganisms.

Effects of various plasticizers on the mechanical properties, water resistance and aging of thermo-moulded films made from sunflower proteins

Abstract The thermoplastic potential of a sunflower protein isolate (ISFP) was studied with the aim of obtaining films of biodegradable polymers. Several polyalcohols (ethylene glycol (EG), propylene glycol (PG), polyethylene glycols (PEGs), polypropylene glycols (PPGs)) were tested as protein plasticizing agents. Five plasticizers were chosen (glycerol, ethylene glycol, diethylene glycol, triethylene glycol and propylene glycol). These agents all produced soft, brown, smooth films with good mechanical properties (σ ma =6.2–9.6 MPa; e max =23–140%) with a high level of impermeability to water vapor (1.9–9.9×10 −12 g m −1 s −1 Pa −1 ). However, these films were only moderately resistant to water (due to the migration of hydrophobic plasticizers into the water). Changes in the mechanical properties of these films also were studied over time and a loss of lowest-boiling point plasticizers was showed. However, no marked loss of glycerol or TEG was observed over the 3-month aging period. Thus, those plasticizers seems to be the most suitable plasticizers for sunflower proteins.

Effects of additives on the mechanical properties, hydrophobicity and water uptake of thermo-moulded films produced from sunflower protein isolate

The mechanical properties and water resistance of thermo-moulded films made from a sunflower protein isolate plasticized with glycerol (ratio 2:1, w/w) were studied. Various cross-linked or hydrophobic components (aldehydes, plant tannins, alcohols and fatty acids) were added and the properties of the films obtained with those of control films (containing no additives other than the plasticizer) were compared. The use of octanoic acid resulted in high tensile strength (7 MPa), whereas the use of octanol resulted in great increase in tensile elongation (54%). Plant tannins gave films with properties similar to those obtained with aldehydes, but without the toxicity. The network of proteins formed by thermo-moulding is water-resistant, regardless of which additives were used or their nature.

DSC study on the thermal properties of sunflower proteins according to their water content

The use of sunflower protein isolate for the manufacturing of biodegradable materials by thermomechanical means requires a characterization of its thermal properties. After modelling of its hydration properties, DSC analysis shows a relaxation phenomenon at 60°C and makes it possible, despite the changes in state of the absorbed water, to determine its glass transition temperature. The evolution of this temperature according to the water content of the samples is then modelled and compared to that of more common proteins.

An automated test for measuring polymer biodegradation

The biodegradability of polymer materials as evaluated by the modified Sturm test is labor-intensive, cumbersome and costly and also tends to cumulate errors. An automated system for the measurement of carbon dioxide would overcome many of these disadvantages. We describe here a method in which CO2 was determined by IR spectroscopy. We compared the results with those from trapping CO2 in a solution of barium hydroxide (Ba(OH)2) followed by manual titration. The automated system was more reproducible, less costly and more compact. The automated system could also be employed to measure the biodegradability of other substances such as oils and detergents.

Evaluation of Material Biodegradability in Real Conditions–Development of a Burial Test and an Analysis Methodology Based on Numerical Vision

This work validated a burial protocol for in situ testing and presents a robust, repeatable and time-saving technique to measure degraded areas in the sample, i.e. an image analysis method. 1440 specimens of degraded samples have been compiled in a data base. To this end, twenty samples presenting different levels of biodegradability (i.e. PHBV/HV, PLA, PCL, PCL-Starch, paper, PE, PE-Starch) were buried at 4 different locations and then disinterred at 4, 6, 9, 12, 18, and 24-month intervals. The biodegradation levels of these samples were determined by computing weight and area loss. Weight loss was measured after careful cleaning, whereas area loss was quantified using image analysis. Image analysis gives reliable information on visual pollution while only requiring a rudimentary and thus quicker cleaning of the samples.

Sunflower cake as a natural composite: composition and plastic properties.

Nowadays, the end-of-life of plastic products and the decrease of fossil energy are great environmental problems. Moreover, with the increase of food and nonfood transformations of renewable resources, the quantities of agro-industrial byproducts and wastes increase hugely. These facts allow the development of plastic substitutes made from agro-resources. Many researches show the feasibility of molding biopolymers extracted from plants like a common polymeric matrix. Other natural macromolecules are used like fillers into polyolefins, for example. However, limited works present results about the transformation of a natural blend of biopolymers into a plastic material. The aim of this study is the determination of the composition of sunflower cake (SFC) and also the characterization of its components. These were identified by chemical and biochemical analysis often used in agricultural or food chemistry. Most of the extraction and purification processes modify the macrostructure of several biopolymers (e.g., denaturation of proteins, cleavage or creation of weak bonds, etc.). So, the composition of different parts of the sunflower seed (husk, kernel, and also protein isolate) was determined, and the plasticlike properties of their components were studied with thermogravimetric analysis, differential scanning calorimetry, and a dynamic mechanical thermal analysis apparatus. Finally, this indirect way of characterization showed that SFC can be considered a natural composite. In SFC, several components like lignocellulosic fibers [40%/dry matter (DM)], which essentially come from the husk of sunflower seed, can act as fillers. However, other biopolymers like globulins ( approximately 30% of the 30% of sunflower seed proteins/DM of SFC) can be shaped as a thermoplastic-like material because this kind of protein has a temperature of glass transition and a temperature of denaturation that seems to be similar to a melting temperature. These proteins have also viscoelastic properties. Moreover, SFC has similar rheological properties and other physicochemical properties compatible with shaping or molding behaviors of plastic-processing machinery.

Modelling Easily Biodegradability of Materials in Liquid Medium-Relationship Between Structure and Biodegradability

In the present project, twenty materials (e.g., polyhydroxybutyrate-hydroxyvalerate, polycaprolactone, cellulose acetate, polyacticacid, polyethylene), representing varied biodegradability levels were studied. An aerobic respirometric test, based on the CEN Draft, was setup. The biodegradability of each plastic film was evaluated by measuring the percentage of carbon converted into CO2 during 35 days. The values of the CO2 production were plotted versus days as a cumulative function. In order to reduce its number of points, the cumulative curve was modeled using a sigmoid function (Hill sigmoid). This model was compared to one found in the literature. A χ i 2 test showed that the biodegradation curve was more accurately fitted with the model than the previous one. Three kinetic parameters were determined by this “Hill model”: one represents the maximal percentage of carbon converted into CO2, the second the “half-life time” in days of the degrading part of the material and the third one the curve radius.

Microwave esterification of sunflower proteins in solvent-free conditions

The esterification of storage proteins from sunflower seeds renders these molecules more hydrophobic and increases internal plasticization, facilitating their use in the fabrication of materials by thermo-mechanical processes. The reaction was carried out in solvent-free conditions to simplify the process and to reduce costs. Optimization of esterification by the classical method, heating in a thermostat-regulated oil bath, resulted in 84% esterification for a reaction time of 4 h (amount of catalyst = 3.9 meq 5 N HCl/g protein, T = 90 degrees C). Microwave heating was then used to reduce the reaction time and the hydrolysis of protein chains. A similar level of esterification (89%) was obtained in 18 min (amount of catalyst = 3.4 meq 5 N HCl/g protein, microwave power (P) = 560 W). High yields were obtained with this method, demonstrating that this process limited hydrolysis.

Fatty Esterification of Plant Proteins

The present work opens new outlets for the valorization of plant proteins by chemical modification. Sunflower and wheat gluten proteins were esterified by n-octanol in the presence of an acid catalyst. By varying reaction parameters (temperature, catalyst concentration, reaction time), the optimum reaction conditions of esterification were defined. The esterification yield for each type of proteins was obtained with a maximum for sunflower proteins. The difference was attributed to their own structure and composition. Furthermore, an increase of amino groups was observed indicating a hydrolysis phenomenon of proteins. The esterification was accompanied by a loss of weight due to a loss of small peptides in solution. However, the reaction leads to chemically-modified proteins with new functional properties. In both cases, the esterified proteins were less soluble at basic pH compared to native proteins, indicating thus a hydrophobation effect.