In Belgium like in Europe, hemp has generated a renewed and growing interest for about ten years. Indeed, it has significant environmental benefits at a time when sustainability is on everyone’s lips.
Its multiple uses suggest a prosperous future to its value chain, making its culture a reliable investment for farmers. In addition to the traditional special papers, textiles, ropes and litters, its applications are growing in the areas of insulation and composite materials.
At the heart of the interactions between the Polychanvre partners, a cross-border thesis aims to define a process of incorporation of hemp (chopped stems) in a synthetic polymer matrix for the efficient production of composite materials for applications such as automobile (molded parts) and construction (extruded profiles). The ultimate goal is to achieve agrocomposites with the same mechanical characteristics as synthetic composites.
The mechanical behaviour of composite materials is highly dependent on the interactions between fibre and matrix which occur during the processing phase and the shaping of the composite. This link, which consists of one or more interphases and interfaces, governs the mechanical behaviour of the material.
The interphase represents the concentric zone to the fine fibre of well-defined chemical nature. It can also be a thin layer deliberately introduced (coupling agent) in order to protect the fibre or to control the interfacial bonding.
Three action areas have been identified:
1. Study of microstructure and interfaces
The work aims to characterize the raw material, chopped stalks of hemp, for the understanding and control of phenomena influencing the behaviour of the material during its processing.
2. Study of mixing methods and composite formulation
Formulation is the first step of processing a material. It consists of selecting suitable additives for the processing: stabilizers, lubricants, process aids, coupling agents.
The formulation work involves testing many formulas to find the best combinations of additives and optimal concentrations.
It allows to:
- improve the thermal and environmental stability of composites
- optimize the mechanical properties of composites
- optimize the matrix / fibre ratio.
3. Characterization and evaluation of the composite (profiles) performance
The analysis will give us information on the behaviour of composite materials manufactured according to the microstructural parameters. The following aspects will be investigated:
- morphology of the matrix, fibre – matrix interface and fibre arrangement,
- short- and long-term mechanical behaviour, fatigue, impact, stress-strain, fracture behaviour,
- environmental effects on mechanical performance,
- physicochemical characterization (thermal degradation, biodegradation, aging, solvent and ultraviolet resistance).
CHARACTERIZATION OF HEMP AS A MATERIAL
At first, the Polychanvre partners will work to characterize the product supplied by ChanvrEco and its ability to be used for the production of composite materials.
For this, a description and detailed characterization of the raw material used in Polychanvre are planned.
The first level of characterization will be carried out on the macroscopic scale (image analysis, classification and groups of fibres/particles, qualitative and quantitative distribution based on form factors). The biochemical characterization of the constituents of each sample will complete the panel of the general properties of the fibre material used for the study, in order to determine its potential and ability to be functionalised.
In a second step, depending on the desired quality criteria, a laboratory-scale preparation of different populations of fibres suitable for the application will be performed (fractionation).
STUDY OF THE POLYMER-HEMP INTERFACE
Following the characterization of the hemp material, the development of a coupling agent is expected to improve the fibre-matrix interface and the final properties of the composites. This additive will be selected or synthesized to functionalize the hemp material.
This is an innovative approach in the field of PVC-natural fibre composites. Indeed, despite some scientific publications, there is no coupling system that is technically satisfactory for PVC-natural fibre composites. PVC-wood products that are on the market contain no coupling agent.
The surface properties of the fibres will then be determined, to monitor the effectiveness of the changes, and optimise the kinetics and stoichiometries.
COMPOSITES FORMULATION AND ELABORATION
The hemp material studied and optimized will be incorporated into a thermoplastic matrix for the elaboration of a mechanically efficient polymer-hemp composite. The choice of the polymer is in fact limited by the degradation of the natural fibres at temperatures above 200°C. The thermoplastics considered are commodity thermoplastics such as PVC and polyolefins or biopolymers such as PLA. The mixture of the hemp material and the polymer will be performed by extrusion. A preliminary step of compaction will be considered to facilitate the introduction of hemp fibres into the extruder. To improve the mechanical properties, the composite formulation will be optimised (hemp content, concentration of the different additives such as lubricants, process aid agents or stabilizers in the case of PVC).
The INTERREG IV France – Wallonia – Vlaanderen program is a European program of cross-border cooperation which aims at strengthening the economic and social exchanges between the regions of Nord-Pas de Calais / Champagne-Ardenne / Picardie in France and Wallonia / Flanders in Belgium.
The program covers a territory of more than 62.000 km ² with a population of about 10,5 million inhabitants. The envelope allocated to the realization of concrete projects is about 276 million euro among which 138 million euro of European cofinancing.
Four priorities are privileged in the implementation of the program:
- Favor the economic development of the zone;
- Develop and promote the identity of the cross-border territory;
- Strengthen the feeling of membership in a common space;
- Revitalize the common management of the territory.