Hélène Angellier-Coussy

The molecular structure of waxy maize starch nanocrystals

The insoluble residues obtained by submitting amylopectin-rich native starch granules from waxy maize to a mild acid hydrolysis consist of polydisperse platelet nanocrystals that have retained the allomorphic type of the parent granules. The present investigation is a detailed characterization of their molecular composition. Two major groups of dextrins were found in the nanocrystals and were isolated. Each group was then structurally characterized using beta-amylase and debranching enzymes (isoamylase and pullulanase) in combination with anion-exchange chromatography. The chain lengths of the dextrins in both groups corresponded with the thickness of the crystalline lamellae in the starch granules. Only approximately 62 mol% of the group of smaller dextrins with an average degree of polymerization (DP) 12.2 was linear, whereas the rest consisted of branched dextrins. The group of larger dextrins (DP 31.7) apparently only consisted of branched dextrins, several of which were multiply branched molecules. It was shown that many of the branch linkages were resistant to the action of the debranching enzymes. The distribution of branched molecules in the two populations of dextrins suggested that the nanocrystals possessed a regular and principally homogeneous molecular structure.

Controlling pesticide release via structuring agropolymer and nanoclays based materials

The potential use of nanoclays for modulating transfer properties of active agents in bio-sourced polymers was explored. For this purpose, new pesticide formulations were designed by combining wheat gluten, ethofumesate (model pesticide) and three montmorillonites (MMT) using a bi-vis extrusion process. Controlled release properties, evaluated through release experiments in water, were discussed in relation to the material formulations and their resulting structure. Partition coefficients were calculated from experimental data and diffusivity values were identified with a Ficks second law mechanistic model. The effect of temperature on release pattern was also evaluated and the activation energy of diffusion was determined. Ethofumesate release was slowed down for all wheat gluten based-formulations as compared to the commercial product. This slow release effect was increased in the presence of hydrophobic MMTs, due to a higher affinity for ethofumesate than for wheat gluten. Contrarily, hydrophilic MMT, displaying a greater affinity for wheat gluten than for ethofumesate seemed ineffective to slow down its release despite the tortuous pathway achieved through a well-exfoliated structure. To conclude, the release mechanisms would be rather governed by pesticide/MMT interactions than MMT/polymer matrix in the case of a hydrophobic pesticide such as ethofumesate and a hydrophilic matrix such as wheat gluten.

Biodegradable herbicide delivery systems with slow diffusion in soil and UV protection properties.

BACKGROUND New herbicidal formulations were designed by combining wheat gluten (WG), two montmorillonites (MMTs) (unmodified and organically modified) and a model pesticide (ethofumesate), and their performances were assessed through an integrative study conducted in soil using an experimental methodology with data modelling. RESULTS All the WG formulations tested were effective in decreasing the apparent diffusivity of ethofumesate in soil in comparison with the non-formulated active substance. The slow-release effect was significantly more pronounced in the presence of the organically modified MMT, confirming the importance of sorption mechanisms to reduce ethofumesate diffusion. The bioassays undertaken on watercress to evaluate herbicidal antigerminating performances showed that all the WG formulations (with or without MMT) were more effective than both the commercial formulation and the non-formulated ethofumesate, whatever the concentration tested. To explain such results, it was proposed that WG formulations would enable ethofumesate to be more available and thus more effective in inhibiting seed germination, as they would be less prone to be leached by water transport due to watering and also less subject to photodegradation. CONCLUSION The use of pesticide formulations based on wheat gluten and nanoclays appeared to be a promising strategy both to reduce the mobility of pesticides in soil and to protect UV-photosensitive pesticides from photodegradation.

Assessing the potential of quartz crystal microbalance to estimate water vapor transfer in micrometric size cellulose particles

This study aims at assessing the use of a quartz crystal microbalance (QCM) coupled with an adsorption system to measure water vapor transfer properties in micrometric size cellulose particles. This apparatus allows measuring successfully water vapor sorption kinetics at successive relative humidity (RH) steps on a dispersion of individual micrometric size cellulose particles (1 μg) with a total acquisition duration of the order of one hour. Apparent diffusivity and water uptake at equilibrium were estimated at each step of RH by considering two different particle geometries in mass transfer modeling, i.e. sphere or finite cylinder, based on the results obtained from image analysis. Water vapor diffusivity values varied from 2.4 × 10-14 m2 s-1 to 4.2 × 10-12 m2 s-1 over the tested RH range (0-80%) whatever the model used. A finite cylinder or spherical geometry could be used equally for diffusivity identification for a particle size aspect ratio lower than 2.

Characterization of the Interface/Interphase in Natural Fibre Based Composites

There are currently no standardized methods to assess the quality of the interface/interphase in natural fibre reinforced composites. Nevertheless different approaches have been developed and are widely used by the scientific and industrial communities. This last chapter proposes a review of the experimental techniques modelling approaches used to investigate the interface/interphase in natural fibres composites and quantify the interfacial adhesion.

Modification of the Interface/Interphase in Natural Fibre Reinforced Composites: Treatments and Processes

The modification of surface properties of synthetic reinforcement fibres to modify composite interphase performance is mostly achieved by chemical functionalization techniques in aqueous media, and in some cases in organic media. In particular, surface treatments of glass fibres are carried out by the use of complex aqueous chemical systems, known as sizings, including one or more organofunctional silane coupling agents, a film former and other additives, i.e. cationic or non-ionic lubricants, anti-static agents, surfactants, wetting agents, chopping aids, and antioxydants). Natural fibres does not yet benefit from such a technological and scientific background. Thereby, many strategies of bulk and surface modifications are currently developed to implement natural fibres in composite materials applications. In this chapter, the different pre-treatments and functionalization treatments and related processes developed to modify natural fibres and interfacial properties in biocomposites will be exposed.

Introduction on Natural Fibre Structure: From the Molecular to the Macrostructural Level

Natural fibres are complex hierarchical bio-assemblies built-up of several biopolymers. In this chapter, the main features related to biopolymers organization within natural fibres are described. Then, the specific surface properties and porous structure of natural fibres that are key parameters as regard to fibre and interface modifications are detailed.

Interfaces in Natural Fibre Reinforced Composites: Definitions and Roles

Natural fibres are a real opportunity to replace conventional synthetic fibres in composite applications. However, even if they have several advantages in comparison to synthetic fibres (lightness, carbon balance, price…), their moisture sensitivity, their poor compatibility with polymer matrices and their low thermal stability and flammability makes their modification by chemical or physical treatments essential. In this chapter, the multiple and multi-scale interfaces in natural fibre based composites is described. The importance and role of the fibre/matrix interface on mechanical performances and durability, and main strategies to enhance the interfacial adhesion is discussed. Finally, an opening towards new functionalities that could be achieved by fibre and interface modifications is addressed.

Lignocellulosic Fibres-Based Biocomposites Materials for Food Packaging

Current requests in the field of food packaging lead to the reasoned design of materials able to improve the global environmental balance of the food/packaging system by minimizing the negative environmental impact of the packaging material while improving its positive role in the food wastes and losses reduction that strongly impact our environment. This means to simultaneously control food degradation reactions while limiting undesirable migrations of additives from packaging towards in respect of our health and remaining economically competitive. The substitution of oil-based materials by ones issued from renewable and non-food resources (e.g. issued from bioconversion of agro-food wastes, for example) and furthermore, fully biodegradable in natural conditions is also a necessity and represents a significant breakthrough from the research in the field of food packaging. In this context, increasing attention is given to full-biocomposites, i.e. composite materials based on constituents all biosourced and biodegradable. Developing full-biocomposites for food packaging requires taken into account numerous factors, and this is even more important for complex biodegradable materials due to the gap in knowledge on their behaviour and potentialities in usage conditions. The objective of this chapter is to decipher the state of the art on full-biocomposites by considering the specific stakes relative to the food packaging application. After the first part of introduction, the second part will present the role of packaging to ensure food quality and safety and how it should be designed in such a way to reduce food waste and losses. The third part will present the window of mass transfer properties of full-biocomposites, which is the main functional property when considering the food packaging application. The fourth part will consider the economical competitiveness of full-biocomposites, the fifth part will treat the safety issues and the sixth of the different options of end of life and waste management.

Characterization of the Fibre Modifications and Localization of the Functionalization Molecules

As pointed out by George et al. (Polym Eng Sci 41(9):1471–1485, 2001), a clear understanding of the complex nature of surfaces in lignocellulosic substrates is needed to optimize modification procedures and thus to increase the usefulness of lignocellulosic biomass as a constituent of composite materials in technical applications. Surface chemistry and topographical features of the fibres are key parameters that influence chemical bonding and mechanical interlocking with polymer matrices, and hence govern the wetting and adhesion/adherence processes in natural fibre reinforced composites. This chapter proposes a comprehensive description of the different approaches used to characterize natural fibres modifications.