Zaida Ortega

Anisotropy of Photopolymer Parts Made by Digital Light Processing

Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this characteristic. Design for this technology and photopolymers becomes a challenge because the manufacturing process and post-processing strongly influence the mechanical properties of the part. This paper shows experimental work to demonstrate the particular behavior of parts made using DLP. Being different to any other AM technology, rules for design need to be adapted. Influence of build direction and post-curing process on final mechanical properties and anisotropy are reported and justified based on experimental data and theoretical simulation of bi-material parts formed by fully-cured resin and partially-cured resin. Three photopolymers were tested under different working conditions, concluding that post-curing can, in some cases, correct the anisotropy, mainly depending on the nature of photopolymer.

Banana and Abaca Fiber-Reinforced Plastic Composites Obtained by Rotational Molding Process

Natural fibers can be used in rotational molding process to obtain parts with improved mechanical properties. Different approaches have been followed in order to produce formulations containing banana or abaca fiber at 5% weight, in two- and three-layer constructions. Chemically treated abaca fiber has also been studied, causing some problems in processability. Fibers used have been characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), optical microscopy, and single-fiber mechanical tests. Rotomolded parts have been tested for tensile, flexural, and impact properties, demonstrating that important increases in elastic modulus are achieved with these fibers, although impact properties are reduced.

Production of banana fiber yarns for technical textile reinforced composites

Natural fibers have been used as an alternative to synthetic ones for their greener character; banana fibers have the advantage of coming from an agricultural residue. Fibers have been extracted by mechanical means from banana tree pseudostems, as a strategy to valorize banana crops residues. To increase the mechanical properties of the composite, technical textiles can be used as reinforcement, instead of short fibers. To do so, fibers must be spun and woven. The aim of this paper is to show the viability of using banana fibers to obtain a yarn suitable to be woven, after an enzymatic treatment, which is more environmentally friendly. Extracted long fibers are cut to 50 mm length and then immersed into an enzymatic bath for their refining. Conditions of enzymatic treatment have been optimized to produce a textile grade of banana fibers, which have then been characterized. The optimum treating conditions were found with the use of Biopectinase K (100% related to fiber weight) at 45 °C, pH 4.5 for 6 h, with bath renewal after three hours. The first spinning trials show that these fibers are suitable to be used for the production of yarns. The next step is the weaving process to obtain a technical fabric for composites production.

Recycling of polymeric fraction of cable waste by rotational moulding

This study focuses on the mechanical recycling of polymeric waste that is produced in considerable amount from the cable industry. Every year large amounts of cables become waste; wires recycling has traditionally focused on metal recovery, while the polymer cover has just been considered as a residue, being landfilled or incinerated. Nowadays, increasingly restrictive regulations and concern about environment make necessary to reduce landfilling as much as possible. Main novelty of the study is that the material used in the research is a post-consumer material and the entire residual material is used, without a previous purification, in contrast with similar studies. Characterization of this residue was performed by thermal analysis, showing that the material is mainly made up of a heavy fraction (84% of the residue), which is not able to melt, fact what makes recycling more difficult. Once characterized, the material was ground, blended with virgin polyethylene and reprocessed by rotational moulding. The influence of the amount of residue and parts structure (1, 2 and 3 layers) was assessed, studying the mechanical behaviour of obtained parts (tensile, flexural and impact properties). It has been found that although mechanical properties get reduced with the increased amount of residue, up to a 35% of residue can be used without an important decrease in mechanical properties. On the other hand, the use of multiple layers in the mouldings allowed obtaining a better external appearance without compromising the mechanical properties.

Predictive coalescence modeling of particles from different polymers: application to PVDF and PMMA pair

This paper aims to study the coalescence phenomenon of two different polymers PVDF and PMMA. The paper is divided in two parts: the first part is devoted to the experimental work, and the second one focuses on the modeling of the coalescence phenomenon. The first step was a physicochemical and rheological characterization. Then, the coalescence tests have been performed on droplets derived from PVDF and PMMA polymers using a polarized light optical microscope combined with a hot stage. The effect of several significant parameters like temperature and particle size was investigated. The second part of this study is focused on the modeling of the coalescence phenomenon based on the well-known Bellehumeur model. The latter has been commonly used to describe the coalescence phenomenon between identical grains. The novelty of the present work consists in the extension of the coalescence model to wider describe the coalescence phenomenon between grains of different polymers. In addition, probabilistic analysis was performed in order to investigate the effect of the parameters governing the coalescence model, namely the viscosity, the surface tension and the relaxation time. The results have shown a good compromise between the experimental results and the predictive generalized Bellehumeur model.

Rapid Manufacturing Experience in Training

Rapid Manufacturing (RM) is considered as a set of innovative manufacturing technologies, many of which are in continuous development phases, and are becoming increasingly important to develop new products with high added value. Procesos de Fabricación research group, at the University of Las Palmas de Gran Canaria (ULPGC) is a founding member of the Spanish Rapid Manufacturing Association (ASERM), and has over ten years of expertise in research, transfer and training activities in these new technologies. ASERM, marked among its strategic objectives to promote and support RM training. As a result of this, the association participates in the European Project named Knowledge Transfer of Rapid Manufacturing (KTRM). Ingeniería de Fabricación educational innovation group (GIEIF) from ULPGC is working along other partners in this project and other training activities, because of the knowledge gained in these technologies.

Knowledge Transfer and Standards Needs in Additive Manufacturing

Although AM technologies have high potential in terms of productivity and competitiveness for companies, their diffusion is still relatively limited among manufacturers and end users. In the context of two European Projects (KTRM and SASAM), this chapter presents an approach of how to transfer knowledge to people working in the manufacturing industry or design. This transfer of knowledge is not only based on technology itself but also on any other relevant issues such as business models or standardization in the field of AM. A survey and road map are presented to show the needs of the AM community in terms of training and standards. Also, the chapter highlights that the new standards and technical reports, from ISO-ASTM, can provide valuable support for knowledge transfer, being the link between training and the implementation of standards a key factor to spread AM technologies. The structure, proposed by ISO TC261 and ASTM F42, for development of future standards, is shown as the most suitable to follow in terms of training as well.

Three-dimensional printed polycaprolactone-microcrystalline cellulose scaffolds: 3D PRINTED POLYCAPROLACTONE-MICROCRYSTALLINE

Microcrystalline cellulose (MCC) is proposed in this study as an additive in polycaprolactone (PCL) matrices to obtain three-dimensional (3D) printed scaffolds with improved mechanical and biological properties. Improving the mechanical behavior and the biological performance of polycaprolactone-based scaffolds allows to increase the potential of these structures for bone tissue engineering. Different groups of samples were evaluated in order to analyze the effect of the additive in the properties of the PCL matrix. The concentrations of MCC in the groups of samples were 0, 2, 5, and 10% (w/w). These combinations were subjected to a thermogravimetric analysis in order to evaluate the influence of the additive in the thermal properties of the composites. 3D printed scaffolds were manufactured with a commercial 3D printer based on fused deposition modelling. The operation conditions have been established in order to obtain scaffolds with a 0/90° pattern with pore sizes between 450 and 500 µm and porosity values between 50 and 60%. The mechanical properties of these structures were measured in the compression and flexural modes. The scaffolds containing 2 and 5% MCC have higher flexural and compression elastic modulus, although those containing 10% do not show this reinforcement effect. On the other hand, the proliferation of sheep bone marrow cells on the proposed scaffolds was evaluated over 8 days. The results show that the proliferation is significantly better (p < 0.05) on the group of samples containing 2% MCC. Therefore, these scaffolds (PCL:MCC 98:2) have suitable properties to be further evaluated for bone tissue engineering applications.

Banana Fiber Processing for the Production of Technical Textiles to Reinforce Polymeric Matrices

Banana fibers have been extracted by mechanical means from banana tree pseudostems, as a strategy to reevaluate banana crops residues. Extracted long fibers are cut to 45 mm length and then immersed into an enzymatic bath for their refining. Conditions of enzymatic treatment have been optimized to produce a textile grade of banana fibers, which have then been characterized. This fiber has then been transformed into yarns and woven to produce a technical textile with different textile structures. Woven material was then used to produce a composite by compression molding, using polypropylene (PP) as polymeric matrix.

Nickel–copper electroforming process applied to rotational mould starting from additive manufacturing

This paper focuses on the development of a more energy-efficient mould for rotational moulding of plastic parts where the tool is made by electroforming of two materials (Ni–Cu), starting from a model of additive manufacturing. Studies on the poor adhesion between nickel and copper layer have not been previously carried out. The paper presents the entire design process of the mould, the electroforming process and activation procedures, and the mould testing under real conditions, comparing it with a conventional CNC machined aluminium mould. Also presented is an experimental study of different treatments of electroformed Ni substrate to provide good adherence for the electroforming of Cu. The best treatment (nitric acid) was applied to a mould for rotational moulding. The main findings of the work are a viable approach for good adherence between Ni and Cu, the advantage of additive manufacturing and electroforming as well as the standardisation of such innovative tooling in rotational moulding.