Polymer blends and composites from renewable resources

Biodegradable composites based on lignocellulosic fibers—An overview

Characterization and Properties of Natural Fiber Polymer Composites: A Comprehensive Review

Wood-plastic composites as promising green-composites for automotive industries!

Elevated environmental awareness of the general public in reducing carbon footprints and the use nonnaturally decomposed solid wastes has resulted in an increasing use of natural materials, biodegradable and recyclable polymers and their composites for a wide range of engineering applications. The properties of natural fibre reinforced polymer composites are generally governed by the pre-treated process of fibre and the manufacturing process of the composites. These properties can be tailored for various types of applications by properly selecting suitable fibres, matrices, additives and production methods. Besides, due to the complexity of fibre structures, different mechanical performances of the composites are obtained even with the use of the same fibre types with different matrices. Some critical issues like poor wettability, poor bonding and degradation at the fibre/matrix interface (a hydrophilic and hydrophobic effect) and damage of the fibre during the manufacturing process are the main causes of the reduction of the composites’ strength. In this paper, different manufacturing processes and their suitability for natural fibre composites, based on the materials, mechanical and thermal properties of the fibres and matrices are discussed in detail.

https://site.icce-nano.org/Clients/iccenanoorg/hui%20pub/2013%20critical%20factors%20on%20manufacturing%20processes%20of%20natural%20fibre%20composites.pdf

Critical factors on manufacturing processes of natural fibre composites

Voids are often present in composite materials and have, as may be expected, negative effects on the mechanical properties. As a consequence, it is regarded to be important to optimise manufacturing techniques of composite materials towards minimum void content. However, it is not obvious that voids also have negative effects on the properties of a structure since those are not just determined by the properties of the material, but also by the dimensions. For a given mass of material, void will increase the dimensions and as a result, for example, the moment of inertia. Thus in principle, it is possible that void may actually have positive effects on the properties of a structure. In this paper this hypothesis is evaluated by studying the influence of void content on the flexural properties of beams manufactured by compression moulding multiple unidirectional commingled glass/polypropylene fibre tows. By varying the time under moulding pressure, beams with void contents between 1 and 14% could be manufactured (with the mass, width and length fixed, and thus only the height free). As expected, voids were found to have a negative effect on the flexural modulus and strength, which both decreased by about 1.5% for each 1% of voids. However, what is more interesting is the fact that voids actually had a clear positive effect on the beam stiffness EI ; which increased by about 2% for each 1% of voids. For example, beams which contained 14% porosity exhibited about 28% higher EI than beams with less than 1% porosity. Moreover, the flexural failure load did not decrease up to a void content of 14%. On the contrary, a least square fit suggested a weak increase with void content. It can therefore be concluded that, in this case, voids actually have positive effects on the structural flexural performance.

The influence of void content on the structural flexural performance of unidirectional glass fibre reinforced polypropylene composites

Novel Pulp Fibre Reinforced Thermoplastic Composites

A process has been developed where multiple yarns of commingled glass and polypropylene are heated and placed to a desired geometry. The placed unidirectional (UD) tow is then encapsulated by over-moulding with glass mat thermoplastics (GMTs). The effects of both force (2080 N), with an equivalent pressure range of 846 bar, and the displacement rate (20100 mm/s) during tow placement on void content and flexural modulus were investigated for nine placement conditions. Placement rate affected the tow quality measured before overmoulding. Void contents were reduced after over-moulding. The volume fraction of UD tow (vol. O8 composite/vol. total composite) in the manufactured multi-material structure was 21.5%. Corresponding tensile tests showed a factor of 2 increase in modulus and a factor of 3 increase in strength relative to GMT. Tow placement rate had no significant effect on tensile properties after over-moulding. Tensile behaviour as a function of the UD tow volume fraction was modelled and predicted values agreed with the experimental results. Additionally, the predicted tensile performance of UD tow reinforced GMT has been compared with possible competitive materials using merit indices.

/pdf/robotic-tow-placement-for-local-reinforcement-of-glass-mat-2r0cidt9q6.pdf

Robotic tow placement for local reinforcement of glass mat thermoplastics (GMTs)

The deformation and fracture behaviour of a generic injection moulded structure reinforced by a robotically placed commingled glass fibre/polypropylene UD-tow (uni-directional) was simulated by finite elements. The suitability of modelling hybrid structures using features available within commercial finite element programs and standard material properties was assessed. Two different 2D modelling approaches based on shell and beam elements, which were computationally less intensive, were evaluated against 3D solid element models in both bending and flexure. It was shown that all three approaches predict the global deformation behaviour in both tension and bending compared with experimental data. Differences between the 2D and 3D approaches were mainly in the predicted stress distribution around the load introduction points.

Finite element modelling and testing of an injection moulded generic tow reinforced structure

To investigate thermoplastic composite structures combining multiple material forms and processing techniques, a generic beam tool was developed that enabled over-moulding of stamped fabrics and robotically placed unidirectional tows (UDtow). Beams produced from different material and process combinations were tested in flexure. Compared with a glass mat thermoplastic (GMT) beam, the maximum force for ‘free-free’ and ‘fixed-fixed’ end conditions was respectively increased by: 30% and 242% for GMT/UDtow, 69% and 224% for GMT/fabric, and 79% and 460% for GMT/UDtow/fabric. Compared with a plain short glass fibre injection moulded (IM) beam, the maximum force for ‘free-free’ and ‘fixed-fixed’ end conditions was respectively increased by: 26% and 213% for IM/UDtow, 64% and 286% for IM/fabric, and 63% and 411% for IM/UDtow/fabric. Standard in-mould cycle times and tool temperatures (50C) were used. The fabric over-moulding process window was examined in detail. The fabric preheat temperature dominated the process. Both global beam testing and coupon-based testing showed that the average interfacial temperature between the fabric insert and the over-moulded material at the moment of contact needed to be above the melt temperature of the polymer. The inserts did not need to be heated above melt temperature, thereby maintaining integrity during the high pressure over-moulding processes.

P.-O. Hagstrand

Papers

The influence of void content on the structural flexural performance of unidirectional glass fibre reinforced polypropylene composites

Novel Pulp Fibre Reinforced Thermoplastic Composites

Robotic tow placement for local reinforcement of glass mat thermoplastics (GMTs)

Finite element modelling and testing of an injection moulded generic tow reinforced structure

Hybrid thermoplastic composite beam structures integrating UD tows, stamped fabrics, and injection/compression moulding