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Biobased composites offer unique properties in the context of sustainable material production as well as end-of-life disposal, which places them as viable alternatives to fossil-fuel-based materials. However, the large-scale application of these materials in product design is hindered by their perceptual handicaps and understanding the mechanism of biobased composite perception, and its constituents could pave the way to creating commercially successful biobased composites. This study examines the role of bimodal (visual and tactile) sensory evaluation in the formation of biobased composite perception through the Semantic Differential method. It is observed that the biobased composites could be grouped into different clusters based on the dominance and interplay of various senses in perception forming. Attributes such as Natural, Beautiful, and Valuable are seen to correlate with each other positively and are influenced by both visual and tactile characteristics of the biobased composites. Attributes such as Complex, Interesting, and Unusual are also positively correlated but dominated by visual stimuli. The perceptual relationships and components of beauty, naturality, and value and their constituent attributes are identified, along with the visual and tactile characteristics that influence these assessments. Material design leveraging these biobased composite characteristics could lead to the creation of sustainable materials that would be more attractive to designers and consumers.

Regeneratcellulosefasern werden aus pflanzlicher Cellulose regeneriert und weisen hinsichtlich ihrer physikalischen und mechanischen Eigenschaften ein interessantes Potenzial auf, um auch in Faserverbundwerkstoffen eingesetzt zu werden. Sie sind biologisch abbaubar und werden derzeit schwerpunktmäßig für die Herstellung von Textilien, Hygieneartikeln, Filtern und Papier eingesetzt. Im Gegensatz zu Naturfasern können sie in reproduzierbarer Qualität hergestellt werden und unterliegen keinen anbau- oder umweltbedingten Schwankungen. Trotz allem wird ihr Potenzial für die Verwendung in Verbundwerkstoffanwendungen bisher kaum ausgeschöpft.

During the COVID-19 pandemic, many educators have been required to offer their courses online. A particular challenge is the implementation of practical laboratory experiments in the field of materials science. The central questions are the following: How can students carry out laboratory experiments at home? How are applications on mobile devices helpful in this context? How can experiments be organized to make students approach the topic with self-motivation and excitement? The concept presented in this paper combines the idea of practical work and the use of an augmented reality app. Guided by a well-structured online learning platform, video tutorials, and lab handouts, students were able to carry out their experiments from home. The results of the evaluation of this new laboratory experiment concept suggest that students very positively welcomed this form of education.

Due to the increasing discussion about sustainable and CO2-reduced materials, the demand for cellulose-based fibres as a reinforcing component in thermoplastic composites has increased considerably. Knowledge about the possibilities of modifying fibres for improved adhesion to the plastic matrix is essential in this context. The fibre/matrix adhesion in cellulose fibre-reinforced polymers is of considerable importance for the design of composite materials. Unfortunately, there are no standards for many essential methods to determine fibre/matrix adhesion. In this review article, various methods for measuring the interfacial shear strength between fibres and matrix, as an indirect characterisation of adhesion, are presented. Additionally, a brief overview of different methods for surface modification of cellulose fibres to improve the adhesion to a thermoplastic matrix is given. This review focuses on the fact that the parameters for the production of test specimens as well as the test method itself can vary considerably from study to study. Because of this, the comparison of data from different publications is not always possible. Therefore, in this article, the main influencing factors and differences in the methods are presented and discussed. Based on a systematic review and a clear description and discussion of the methods, the reader is given a broad basis for a better understanding of characteristic values for fibre/matrix adhesion.

International audience; The stinging nettle Urtica dioica L. is a perennial crop with low fertilizer and pesticide requirements, well adapted to a wide range of environmental conditions. It has been successfully grown in most European climatic zones while also promoting local flora and fauna diversity. The cultivation of nettle could help meet the strong increase in demand for raw materials based on plant fibers as a substitute for artificial fibers in sectors as diverse as the textile and automotive industries. In the present review, we present a historical perspective of selection, harvest, and fiber processing features where the state of the art of nettle varietal selection is detailed. A synthesis of the general knowledge about its biology, adaptability, and genetics constituents, highlighting gaps in our current knowledge on interactions with other organisms, is provided. We further addressed cultivation and processing features, putting a special emphasis on harvesting systems and fiber extraction processes to improve fiber yield and quality. Various uses in industrial processes and notably for the restoration of marginal lands and avenues of future research on this high-value multi-use plant for the global fiber market are described.

Funding Information: Albert Hernandez-Estrada wishes to thank the Finnish Cultural Foundation for financial support and COST Action FP1303 for supporting the STSM. Birgit Uhrlaub (HSB—City University of Applied Sciences, Bremen, Germany), and Dr Hans-Jörg Gusovius and Dr Carsten Lühr (Leibniz Institute for Agricultural Engineering and Bioeconomy ATB, Potsdam, Germany) are thanked for processing and providing the hemp. Dr Nina Graupner and Milan Kelch (HSB—City University of Applied Sciences, Bremen, Germany) are thanked for guidance in producing the epoxy composites and in testing the specimens. Niels Kühn (HSB—City University of Applied Sciences, Bremen, Germany) is thanked for the production of the 3D-printed moulds, which facilitated the production of the embeddings in polyurethane resin. Publisher Copyright: © 2021, The Author(s). This work investigated the impact that the processing of hemp (C. sativa L.) fibre has on the mechanical properties of unidirectional fibre-reinforced epoxy resin composites loaded in axial tension, and particleboard reinforced with aligned fibre bundles applied to one surface of the panel. For this purpose, mechanically processed (decorticated) and un-processed hemp fibre bundles, obtained from retted and un-retted hemp stems, were utilised. The results clearly show the impact of fibre reinforcement in both materials. Epoxy composites reinforced with processed hemp exhibited 3.3 times greater tensile strength when compared to the un-reinforced polymer, while for the particleboards, the bending strength obtained in those reinforced with processed hemp was 1.7 times greater than the un-reinforced particleboards. Moreover, whether the fibre bundles were processed or un-processed also affected the mechanical performance, especially in the epoxy composites. For example, the un-processed fibre-reinforced epoxy composites exhibited 49% greater work of fracture than the composites reinforced with processed hemp. In the wood-based particleboards, however, the difference was not significant. Additionally, observations of the fracture zone of the specimens showed different failure characteristics depending on whether the composites were reinforced with processed or un-processed hemp. Both epoxy composites and wood-based particleboards reinforced with un-processed hemp exhibited fibre reinforcement apparently able to retain structural integrity after the composite’s failure. On the other hand, when processed hemp was used as reinforcement, fibre bundles showed a clear cut across the specimen, with the fibre-reinforcement mainly failing at the composite's fracture zone.

Due to good density specific mechanical properties and low carbon footprint, natural fibre-reinforced plastic composites made from fleeces and felts are frequently used as automotive interior parts. The industry targets further mass reduction. Following a biomimetic technology-pull approach, natural fibre-reinforced polypropylene plates with improved lightweight potential were produced using compression moulding. Best results were obtained for a sandwich structure with thin, unidirectional flax fibre layers surrounding a needle felt based core. It was inspired by the carapace structure of the red-eared slider Trachemys scripta elegans. The lay-up performed well, not only with a high density specific flexural stiffness of 2.33 GPa1/3 cm3/g and strength of 9.46 MPa1/2 cm3/g and energy dissipation but also through less abrupt failure due to an asymmetric orientation of unidirectional fibres in the two face sheets. Combined with a mass-reduced needle felt as a core, this concept displays a promising and unconventional approach for further mass reduced, sustainable interior panels used as non-visible and visible design elements in the vehicle.

Die größtmögliche Ausnutzung der Eigenschaften von Fasern ist das Ziel vieler Spinnverfahren. Bislang können die Eigenschaften von Bastfasern in Kurzstapelgarnen für die Verstärkung von Faserverbundwerkstoffen nur unvollständig ausgenutzt werden. Deshalb wird eine neuartige Garnstruktur mit kürzeren drehungsfreien Bastfasern im Garnkern für Halbzeuge und den Einsatz in naturfaserverstärkten Kunststoffen (NFK) für höherbelastete Strukturbauteile entwickelt. Dadurch sollen gute mechanische Eigenschaften der NFK erreicht werden und gleichzeitig der Preis infolge der Verwendung kostengünstigerer Verstärkungsfasern reduziert werden. Zielsetzung ist dabei nicht die reine Substitution der herkömmlichen glasfaserverstärkten Kunststoffe (GFK), sondern die Erschließung neuer Anwendungsfelder durch die Kombination von Glas- und Bastfasern. Um das Ziel umzusetzen haben sich Partner aus Industrie und Forschung zu einer Kooperation im Rahmen eines von der Fachagentur Nachwachsende Rohstoffe (FNR) finanzierten Projektes (NF-CompPlus) zusammengeschlossen. Die Partner sind so ausgewählt, dass alle Schritte in der Fertigungskette vom Rohstoff bis zum Faserverbundwerkstoff einschließlich durchzuführender Prüfungen abgebildet sind.

The study investigates the use of copy paper in poly (butylene adipate terephthalate)-PBAT and polylactide-PLA composites. The influence of paper volume fraction (21, 30 and 48%) on the void content and the composite properties was analysed by using two different compression moulding methods. An increasing fibre content lead to significantly improved tensile characteristics, while the Charpy impact strength showed a toughness decrease for PBAT and an increase for PLA composites. Additionally, layered composites, where either two stiff PLA composite layers enclosed a ductile PBAT composite core or vice versa, were produced with the aim to increase the toughness. Due to the high elongation of PBAT, the insufficient fibre/matrix adhesion and the low fibre length, this goal could not be reached. However, copy paper represents a good reinforcing component achieving a maximum strength of 120 MPa and a tensile modulus of 10.2 GPa at the highest paper volume fraction in PLA.

This work examines size effects of ductile regenerated cellulose fibres (viscose) with different diameters (11.9, 16.6 and 48.4 μm) as well as their unidirectional epoxy composites reinforced with fibre mass fractions of 20, 30 and 40% (16, 25 and 34% in volume). Viscose fibres were tested at different clamping lengths ranging between 2 and 50 mm. Composites were produced in 2 different sizes (cross-sectional area of 6.3 and 41.2 mm2) and tested at different gauge lengths (35 and 100 mm). It was investigated to what extent size effects affect the tensile strength and if the two-parameter least squares Weibull statistics may be used for the prediction of strength values when the sample volume of fibres or composites is changed. The results have shown that the Weibull theory is in principle applicable. It has been found that the prediction accuracy is only sufficient if the Weibull strength is determined on the basis of Weibull parameters determined at small sample volumes for the prediction of data measured with higher specific sample volumes. In this case, all calculated data are within the mean arithmetic deviation of the experimental results. If, on the other hand, the prediction is based on parameters determined for larger sample volumes, a considerable overestimation of the strength data of samples having a smaller sample volume is the result.

The mechanical performance of composites made from viscose fibre reinforcement fabrics and PP matrix polymers could be enhanced by photo-chemical surface modification of the viscose fibres. The surface modification was achieved by deposition of UV-polymerized organic thin layers using pentaerythritol triacrylate or diallylphthalate as monomers. The main effects of the photo-chemical modification refer to a decrease in wettability of the highly hydrophilic and water adsorbing viscose fibres and an increase in their affinity towards non-polar substances. Both effects were found to yield an increase in fibre–matrix adhesion and interfacial shear strength, resulting in better impact and tensile properties compared to untreated samples. The experimental composites were slightly inferior with regard to fibre–matrix adhesion and IFSS than established systems using modified matrix polymers such as the maleic anhydride modified PP, but exhibited similar or even improved properties in view of tensile strength and impact behaviour. The latter indicates superior energy transfer by the thin organic layers forming the fibre–matrix interface. Based on these observations, the studied concept of photo-polymerized inter-layers between fibre and matrix can be understood as a biomimetic concept mimicking the graded transitions of natural structures.

The present study shows a new approach for the prediction of tensile strength values of compression moulded long cellulose fibre-reinforced brittle polylactide (PLA) composites. For this approach regenerated cellulose fibres (lyocell) of variable fineness were used as reinforcement. Composites with different fibre loadings (17, 26 and 36 vol-%) and mean fibre orientation angles ranging between ± 20 and ± 65° were manufactured. Some published models were applied to the mechanical properties of our composites. While the rule of mixture as well as the Kelly-Tyson model lead to a clear overestimation of the strength values, the model of Taha & El-Sabbagh et al. (developed for injection moulded composites) leads to a clear underestimation. On the basis of the Kelly-Tyson-model expanded with Taha & El-Sabbagh et al.'s agglomeration factor and the use of the fibre stress at the point of elongation at break of the composite a new model was created for compression moulded regenerated cellulose fibre-reinforced composites. Overall, 19 different composites were investigated. 13 of them show a deviation from the model data to the measured tensile strength of

The petioles of red rhubarb are load-bearing structures which need to combine sufficient stiffness with high toughness. Although mostly consisting out of water, the petioles showed a remarkable Charpy impact strength, partly based on their beam-like structure: outermost bark fibre bundles provide stiffness and strength, and surround a core reinforced with ductile vascular bundles, which dissipate impact energy at two hierarchical levels: helical fibres in the vascular bundles are straightened, and both helical fibres and bundles are pulled-out of the parenchyma. Using technical composites made from stiff and ductile cellulose fibres as a model system, we investigated the functional significance of the fibre arrangement further. The impact resistance of bio-inspired composites exceeded that of composites with identical fibre-fraction but random fibre-distribution by more than a factor of two, while their tensile and flexural properties did not differ significantly, suggesting promising new routes for the design of tough, bio-compatible composites.

In commercial injection moulding simulation software only tools for glass fibre-reinforced thermoplastics exist, but not for natural fibres. In our research, we adapted a simulation software for sisal fibre-reinforced polypropylene. To evaluate our simulation results, three experimental methods, to measure fibre orientation are compared to each other using injection moulded sisal fibre-reinforced polymer parts: terahertz spectroscopy, μ-CT and light microscopy measurements (LMM) of microtome sections. Terahertz spectroscopy determines the main orientation over the plate thickness, but it neglects variances of fibre orientation across the plate thickness. Using μ-CT and LMM allows measuring fibre orientation at different layers across the plate thickness and to detect a shell-core effect. Care has to be taken comparing results from μ-CT and LMM, due to their differences in the slice thicknesses. The orientation found with the μ-CT correlates well with the injection moulding simulation developed for sisal fibre-reinforced polypropylene.

Hemp (Cannabis sativa L.) is a bast-fiber crop well-known for the great potential to produce sustainable fibers. Nevertheless, hemp fiber quality is a complex trait, and little is known about the phenotypic variability and heritability of fiber quality traits in hemp. The aim of this study is to gain insights into the variability in fiber quality within the hemp germplasm and to estimate the genetic components, environmental components, and genotype-by-environment (G×E) interactions on fiber quality traits in hemp. To investigate these parameters, a panel of 123 hemp accessions was phenotyped for 28 traits relevant to fiber quality at three locations in Europe, corresponding to climates of northern, central, and southern Europe. In general, hemp cultivated in northern latitudes showed a larger plant vigor while earlier flowering was characteristic of plants cultivated in southern latitudes. Extensive variability between accessions was observed for all traits. Most cell wall components (contents of monosaccharides derived from cellulose and hemicellulose; and lignin content), bast fiber content, and flowering traits revealed large genetic components with low G×E interactions and high broad-sense heritability values, making these traits suitable to maximize the genetic gains of fiber quality. In contrast, contents of pectin-related monosaccharides, most agronomic traits, and several fiber traits (fineness and decortication efficiency) showed low genetic components with large G×E interactions affecting the rankings across locations. These results suggest that pectin, agronomic traits, and fiber traits are unsuitable targets in breeding programs of hemp, as their large G×E interactions might lead to unexpected phenotypes in untested locations. Furthermore, all environmental effects on the 28 traits were statistically significant, suggesting a strong adaptive behavior of fiber quality in hemp to specific environments. The high variability in fiber quality observed in the hemp panel, the broad range in heritability, and adaptability among all traits prescribe positive prospects for the development of new hemp cultivars of excellent fiber quality.

Based on the knowledge that plant structures often have graded stiffness transitions between strengthening elements and the surrounding matrix, which result in good damping behaviour and high toughness of the plant structure, the fatigue behaviour of composites made from rayon fibre and polypropylene (PP) as a matrix could be enhanced by photochemical surface modification of the regenerated cellulose fibres. The surface modification was achieved by deposition of UV-polymerized organic thin layers using pentaerythritol triacrylate (PETA) as the monomer. It has been shown earlier that the photochemical modification yields a decrease in wettability of the highly hydrophilic and water adsorbing viscose fibres and an increase in their affinity towards non-polar substances, thus promoting fibre-matrix adhesion. The presented experiments proved that the distinguished mechanical properties of the deposited layer structure also mimic the graded transition and provide good damping and fatigue behaviour superior to either untreated rayon/PP or rayon/maleic anhydride-modified PP composites.

Fibrinogen nanofibers hold great potential for wound healing applications since they mimic the native blood clot architecture and offer important binding sites to support fibroblast adhesion and migration. Recently, we introduced a new method of salt-induced self-assembly to prepare nanofibrous fibrinogen scaffolds. Here, we present our results on the mechanical properties of these scaffolds and their interaction with 3T3 fibroblasts and E. coli bacteria, which we used as model systems for wound healing. Hydrated, nanofibrous fibrinogen scaffolds showed a Young's modulus of 1.3 MPa, which is close to the range of native fibrin. 3T3 fibroblasts adhered and proliferated well on nanofibrous and planar fibrinogen up to 72 h with a less pronounced actin cytoskeleton on nanofibers in comparison to planar fibrinogen. Fibroblasts on nanofibers were smaller with many short filopodia while larger cells with few long filopodia were found on planar fibrinogen. Live cell tracking revealed higher migration velocities on nanofibers in comparison to planar fibrinogen. The growth of E. coli bacteria on nanofibrous fibrinogen was significantly reduced as compared to agar controls with no bacteria migrating through the nanofibers. In summary, we conclude that self-assembled fibrinogen nanofibers could become highly attractive as future scaffolds for wound healing applications.

This manuscript describes the effects of alterations in biochemical composition on structural morphology and the mechanical behaviour of technical fibres of hemp used for composite applications. First, the strength and apparent Young’s modulus distribution of technical fibres of hemp of 96 hemp samples, corresponding to 32 different hemp accessions cultivated in 3 locations, were analysed using Weibull distribution. From these, 2 samples (one with high and one with low fibre strength) were selected for further analysis. Next, full-field strain measurement at the micro-scale during tensile loading via digital image correlation analysis was used for evaluating both, the stress-strain behaviour at a global scale and the local mechanical behaviour heterogeneity at a micro-scale, along a technical fibre of hemp. The analysis reveals 2 typical types of tensile stress-strain curves, and a complex and very irregular pattern of strain concentrations, which are associated to the technical fibre strength. The non-linear behaviour of the stress-strain curve is explained by the development of shear strain at the elementary fibre (botanically defined as the individual cell) interphases. Micro tomography and biochemical analysis of the technical fibre microstructure showed that alterations in cell wall composition, in particular substitution of pectin, leads to changes in the non-linear behaviour of technical fibres of hemp under tensile loading.

Negative size effects are commonly reported for advanced composite materials where the strength of the material decreases with increasing volume of the test specimen. In this work, the effect of increasing specimen volume on the mechanical properties of all-cellulose composites is examined by varying the laminate thickness. A positive size effect is observed in all-cellulose composite laminates as demonstrated by a 32.8% increase in tensile strength as the laminate thickness is increased by 7 times. The damage evolution in all-cellulose composite laminates was examined as a function of the tensile strain. Enhanced damage tolerance concomitant with increasing specimen volume is associated with damage accumulation due to transverse cracking and strain delocalisation. A transition from low-strain failure to tough and high-strain failure is observed as the laminate thickness is increased. Simultaneously, scale effects lead to an increase in the void content and cellulose crystallinity at the core, with increasing laminate thickness.

The scatter in tensile properties induced by the determination and calculation method of the cross-sectional area (CSA) of bast fibre bundles is almost as high as the scatter found in the literature. Different methods (light microscopy, high resolution flat-bed scanning, and laser-based fibre dimensional analysis) were applied to exactly the same flax fibre bundles prior to tensile testing, and different approaches for the calculation of the CSA were applied. The CSA method alone is introducing up to 300 % of variation in tensile strength data. These results show that there is a strong need for standards and standardisation of fibre bundle testing. Care has to be taken when comparing results from studies using slightly different methods.

All-cellulose composites are high performing green materials and solvent infusion processing makes their upscaled manufacturing possible. This study explored the use of aqueous 7 wt.% NaOH/12 wt.% urea solution as cost effective and environmentally friendly cellulose solvent for solvent infusion processing. A short dissolution time of 5 min led to all-cellulose composite laminates with a tensile strength of 114 ± 1.9 MPa and a Young’s modulus of 7.8 ± 0.5 GPa. A decrease of tensile strength and Young’s modulus with increasing dissolution time from 5 to 60 min was linked to changes in composite microstructure and fine structure of the reinforcing rayon fibres. It was shown that aqueous NaOH/urea solution is a promising alternative solvent, as it offers the advantages of shorter processing times and reduced solvent costs by 97%, while resulting in 25% stronger laminates, when compared to using ionic liquids.

Previously conducted studies showed that UD regenerated cellulose fibre-reinforced thermoset composites can obtain specific Charpy impact strength values in the range of glass fibre reinforced composites. Composites of two different viscose fibre types, each with and without an oily avivage, were investigated. Despite similar mechanical properties of the fibres the impact strength of the CR fibre composites was about twice as high as that of the standard fibre composites. To reveal a possible explanation for this effect the fibre surface properties were investigated more closely. AFM measurements showed no differences in fibre surface topologies. However the physico–chemical properties of the fibre types differ. IGC measurements showed that the standard Cordenka fibre without avivage (“ std wo a. ”) possesses a slightly higher specific surface energy and base number (K b ) than the CR fibres without avivage (“ CR wo a. ”) resulting in a better adhesion to the highly polar epoxy. This is also shown by the pair specific interaction parameters (I sp ) and the work of adhesion. Both are clearly higher for the epoxy – “std wo a.” pair. Accordingly the measured fibre pull-out lengths of the CR fibres are one order of magnitude higher than of the std suggesting a weaker interfacial shear strength between the CR fibres and epoxy. Within the same fibre type the samples without avivage show longer pull-out lengths. As a weaker fibre-matrix adhesion causes stronger crack deflection and energy dissipation these results correspond well with the previously measured Charpy impact strengths.

In the present study, the hybridisation of ductile viscose (Danufil) and stiff basalt fibres was investigated. The aim was to combine the positive properties of both fibre types in an epoxy matrix. Composites (round rods) were produced with a fibre volume fraction of 40% with a pultrusion technique from Danufil, basalt and a mixture of Danufil and basalt fibres. The hybrid composites were produced on the one hand with a unidirectional (UD) Danufil core and a UD basalt outer layer and vice versa. On the other hand, a UD core layer of Danufil is covered with a twisted basalt outer layer and vice versa. The results have shown that the most successful hybridisation was realised with the UD composite having a Danufil core and a UD basalt outer layer. An impact strength on the level of the basalt fibre-reinforced composite could be achieved whereby the lightweight construction potential could be improved. The spontaneous failure of the basalt fibre-reinforced composite under bending load could be considerably delayed by the addition of Danufil, whereby the strength, stiffness and temperature resistance were significantly improved by the presence of basalt. For the application of round rods, e.g. in poles for mobile architecture, the load-bearing capacity and the safety aspects could be significantly improved by hybridisation.

The Multihemp biorefinery concept combines processing systems that, starting from harvesting, transform hemp biomass into a spectrum of marketable intermediate and final products. Hackling loss sorted out during production of long hemp was used for the compounding process to produce hemp fibre-reinforced Polylactide (PLA) granules for the injection moulding process. Even though only side stream fibres were used, the overall mechanical properties lie within the range of properties reported for PLA – bast fibre composites cited in the literature or even above. The use of hemp from an earlier harvest at full flowering (harvest 1) significantly increases Young’s modulus values compared to the pure PLA polymer and shows a slightly better reinforcing potential than hemp harvested later at seed maturity (harvest 2). A significant influence of harvest time on the composite properties was found, which is stronger than the variety influence. Based on the presented results, the poly-product MultiHemp system showed a proof of concept for the use of hackling loss for injection moulded composites.

To establish injection-moulded, natural fibre-reinforced polymers in the automotive industry, numerical simulations are important. To include the breakage behaviour of natural fibres in simulations, a profound understanding is necessary. In this study, the length and width reduction of flax and sisal fibre bundles were analysed experimentally during compounding and injection moulding. Further an optical analysis of the fibre breakage behaviour was performed via scanning electron microscopy and during fibre tensile testing with an ultra-high-speed camera. The fibre breakage of flax and sisal during injection moulding was modelled using a micromechanical model. The experimental and simulative results consistently show that during injection moulding the fibre length is not reduced further; the fibre length was already significantly reduced during compounding. For the mechanical properties of a fibre-reinforced composite it is important to overachieve the critical fibre length in the injection moulded component. The micromechanical model could be used to predict the necessary fibre length in the granules.