Presently there are two forms of biological fibre extraction, water retting or dew retting, which use bacteria or fungi, respectively. Microbial action results in release of the cellulose fibres due to modification of the pectin, hemicellulose and lignin content from parenchyma cells and the middle lamellae. Water retting results in pollution, high costs associated with labour and drying, as well as significant waste water production, while disadvantages to dew retting include the need for appropriate climates, variable and inferior fibre quality, risks of over-retting as well as health effects due to dust and fungal contaminants. The overall objective of this research was to explore silage retting as a new pre-processing technique allowing use of available farm infrastructure and contained retting conditions to produce plant-derived fibres with improved physical and chemical characteristics suitable for application in biocomposites. The corn processing ability of the hemp retting agents Clostridium felsineum and Bacillus subtilis was also investigated. Pleiotropic and/or crop management practices were assessed by comparing the physico-mechanical properties and the microbial populations during silage fermentation of genetically equivalent conventional, Roundup Ready® (RR) and Bt-Roundup Ready® (Bt-RR) corn isolines. Potential recovery of volatile organic acids in silage retting effluent as value-added chemicals was also explored. The results indicated that C. felsineum is an effective corn retting agent given the effective release of the fibre bundles from the corn pith, with B. subtilis contributing to the retting process by reducing the oxygen content and providing the required anaerobic conditions for clostridial growth. The native microflora present in the plant phyllosphere also showed some retting ability. Composition, thermostability and mechanical properties of the biocomposites produced using the fibres from the retted corn were all found to vary depending on the variety of corn. Specifically, retted Bt-RR cornstalk showed a 15°C increase in onset of degradation. Divergences between corn silage microbial communities analyzed by community-level physiological and enzyme activity profiling indicated that metabolic shifts were time-, region-, and contaminant-sensitive. Acetic and butyric acid production in silage retting effluent was found to be highest under anaerobic conditions and was also influenced by corn hybrid variety, although a specific variety was not identified as most or least favourable for organic acid production due to high variability. Bt-RR cornstalk material was found to have higher cellulose content and better thermostability with an onset of degradation of up to 45°C higher than its genetic RR and conventional counterparts. However, fibres from the RR corn isoline produced biocomposites with the highest flexural strength and modulus. RR cornstalk-reinforced polypropylene showed a 37 and 94% increase in flexural strength and modulus, respectively when compared to the mechanical properties of the pure polypropylene. The Bt-RR and conventional varieties produced biocomposites with an average increase of 26.5% in flexural strength and 83.5% in flexural modulus. The thermostability of ensiled corn biomass was found to be influenced by region, use of inoculants and silage treatment, while the silage treatment accounted for most of the variability in corn biomass composition. Polypropylene matrix biocomposites produced with (30 wt%) pre- and post-silage corn did not show significant differences in mechanical properties. However, ensiled corn resulted in an increase in fibres and potential microbial biomass of smaller particle sizes with more optimal thermostability and purity, producing biocomposites with higher flexural strength and modulus especially at higher extrusion temperatures. Cornstalk is an effective reinforcement material, producing biocomposites with higher flexural strength, flexural modulus and impact strength. Whole corn biomass presents a potential alternative to other plant fibres, especially as filler material. Silage retting resulted in fibres with a higher thermostability and smaller particle size distribution that, given their already smaller aspect ratio, could result in better mechanical properties in thermoplastics with a higher melting temperature or biocomposites requiring higher shear for mixing.

Presently there are two forms of biological fibre extraction, water retting or dew retting, which use bacteria or fungi, respectively. Microbial action results in release of the cellulose fibres due to modification of the pectin, hemicellulose and lignin content from parenchyma cells and the middle lamellae. Water retting results in pollution, high costs associated with labour and drying, as well as significant waste water production, while disadvantages to dew retting include the need for appropriate climates, variable and inferior fibre quality, risks of over-retting as well as health effects due to dust and fungal contaminants. The overall objective of this research was to explore silage retting as a new pre-processing technique allowing use of available farm infrastructure and contained retting conditions to produce plant-derived fibres with improved physical and chemical characteristics suitable for application in biocomposites. The corn processing ability of the hemp retting agents Clostridium felsineum and Bacillus subtilis was also investigated. Pleiotropic and/or crop management practices were assessed by comparing the physico-mechanical properties and the microbial populations during silage fermentation of genetically equivalent conventional, Roundup Ready® (RR) and Bt-Roundup Ready® (Bt-RR) corn isolines. Potential recovery of volatile organic acids in silage retting effluent as value-added chemicals was also explored. The results indicated that C. felsineum is an effective corn retting agent given the effective release of the fibre bundles from the corn pith, with B. subtilis contributing to the retting process by reducing the oxygen content and providing the required anaerobic conditions for clostridial growth. The native microflora present in the plant phyllosphere also showed some retting ability. Composition, thermostability and mechanical properties of the biocomposites produced using the fibres from the retted corn were all found to vary depending on the variety of corn. Specifically, retted Bt-RR cornstalk showed a 15°C increase in onset of degradation. Divergences between corn silage microbial communities analyzed by community-level physiological and enzyme activity profiling indicated that metabolic shifts were time-, region-, and contaminant-sensitive. Acetic and butyric acid production in silage retting effluent was found to be highest under anaerobic conditions and was also influenced by corn hybrid variety, although a specific variety was not identified as most or least favourable for organic acid production due to high variability. Bt-RR cornstalk material was found to have higher cellulose content and better thermostability with an onset of degradation of up to 45°C higher than its genetic RR and conventional counterparts. However, fibres from the RR corn isoline produced biocomposites with the highest flexural strength and modulus. RR cornstalk-reinforced polypropylene showed a 37 and 94% increase in flexural strength and modulus, respectively when compared to the mechanical properties of the pure polypropylene. The Bt-RR and conventional varieties produced biocomposites with an average increase of 26.5% in flexural strength and 83.5% in flexural modulus. The thermostability of ensiled corn biomass was found to be influenced by region, use of inoculants and silage treatment, while the silage treatment accounted for most of the variability in corn biomass composition. Polypropylene matrix biocomposites produced with (30 wt%) pre- and post-silage corn did not show significant differences in mechanical properties. However, ensiled corn resulted in an increase in fibres and potential microbial biomass of smaller particle sizes with more optimal thermostability and purity, producing biocomposites with higher flexural strength and modulus especially at higher extrusion temperatures. Cornstalk is an effective reinforcement material, producing biocomposites with higher flexural strength, flexural modulus and impact strength. Whole corn biomass presents a potential alternative to other plant fibres, especially as filler material. Silage retting resulted in fibres with a higher thermostability and smaller particle size distribution that, given their already smaller aspect ratio, could result in better mechanical properties in thermoplastics with a higher melting temperature or biocomposites requiring higher shear for mixing.

No / The goal of this study was to investigate the fibre orientation distribution (FOD), and subsequent mechanical properties, of an injection moulded plate with two different number averaged fibre lengths, termed in this paper medium (1.35 mm) and long (2.40 mm). Fibre orientation measurements (FOD) were made using the 2D elliptical section method and an in-house developed image analyser. The samples were injected from a pin gate located at the centre and top of the plate. Expansion flow on the divergent flow front from this pin gate resulted in a core region with circumferential alignment, while through thickness shear resulted in the usual realignment of fibres in the flow direction either side of the core, termed the shell layers. Two interesting aspects were discovered from these measurements. First, and most importantly, the FOD was found to be independent of the two fibre lengths in this study, and so predominantly controlled by the mould shape and the interaction with the flow front. Second, the fibres in the core region were found to be much closer packed than those in the shell regions. The interaction between the flow front and the mould shape resulted in a range of FOD across the moulded plate, from equal in-plane orientation at the centre of the plate, to highly aligned at the plate edge. This gave a very useful set of samples from which to test out the well known modified rule of mixtures (MROM). Often the fibre orientation distribution cannot be measured directly, but indirectly using the modified rule of mixtures model in reverse. The samples from this moulding (at two different average fibre lengths) gave an excellent opportunity to validate this often used approach. Both the tensile modulus and strength (measured parallel to the injection direction) were found to show a strong correlation with the measured fibre orientation, with a significant increase in both measures between the centre and the edge of both plates. The increased length of the ‘long’ fibre plate was found to give only a small increase in tensile modulus but a much larger increase in tensile strength. The tensile modulus showed a linear dependence with the measured fourth order orientation tensor average, 〈cos4 θ〉, with respect to the injection direction of the plate, as predicted by the modified rule of mixtures. Excellent agreement was found between the measured modulus and the predictions from the modified rule of mixtures, based only on measured quantities (matrix modulus, fibre fraction and average fibre length) for both plates.

Nowadays, when environmental concerns are becoming increasingly important are there great interest in natural materials and recyclability. The possibility of reusing materials with maintained mechanical properties are essential for sustainability. Today produced approximately 90,000 tons of natural fiber reinforced composites in Europe of those are 40,000 tons compression molded of which the automotive industry uses 95%. Natural fiber reinforced composites is recyclable and therefore interesting in many applications. Also, natural fiber reinforced composites is inexpensive, light in weight and shows decent mechanical properties which makes them attractive to manufactures. However, the problem with natural fiber reinforced composites is the poor adhesion between fiber and matrix, the sensitivity of humidity and their low thermal stability. Those problems could be overcome by addition of compatibilizer and reactive filler. This study will examine the technical requirement in order to develop a sustainable and recyclable biocomposite. It investigates the composition of matrix (polypropylene), fiber (flax), compatibilizer (maleic anhydride grafted polypropylene) and reactive filler (CaO) in order to obtain various combinations of stiffness, strength and processability. The two main methods used for preparing samples were compounding and injection molding. Results shows that 20 wt% flax was the optimal fiber content and that maleic anhydride grafted polypropylene is a very good compatibilizer by enhancing the strength significant. Surprisingly was the strength impaired due to the addition of CaO. The composition of 20 wt% flax, 1 wt% maleic anhydride grafted polypropylene and 79 wt% polypropylene is the technically most favorable composition.