1- Introduction

2- Natural fibers composites, properties and their applications

3- Processing of natural fiber reinforced composites

4- Additive manufacturing (AM) of composites

5- Challenges and opportunities in AM of natural fiber composites

6- Concluding remarks

References

Abstract

Throughout the world there have been alarming concerns over the use of nonrenewable resources during manufacturing of goods and associated environmental legislations. Therefore, the use of natural materials and fabrication of composites therefrom, particularly, development of natural fiber reinforced polymer composites is gaining significant attention. Although natural fiber reinforced composites (NFRCs) show strong application prospects, various materials and processing related challenges needs to be addressed to achieve long-term stability and performance. In this review, we attempted to provide an overview of different types of natural fibers, their characteristics and properties enabling them to be used as reinforcing agents in different polymers. Then the unique requirement of fiber surface modification to achieve enhanced fiber-matrix bonding is discussed. The article also discusses conventional processing routes and critical issues associated with NFRCs processing. The use of different additive manufacturing (AM) technologies in processing polymer composites is also discussed. At the end, we have critically analyzed the challenges and opportunities associated with AM of NFRCs.

Introduction

Environmentally friendly processes, products and recycling or use of waste are greatly acknowledged not only by scientific community but also by several industries due to mounting concerns over the use of nonrenewable resources. These are critical to the key principles of sustainable manufacturing; namely, reduce, reuse, recycle, recover, redesign, and remanufacture. Environmental legislation such as end-of-life vehicles must be 85% reusable/recycled, 10% used for energy recovery and balance for landfills implemented in Europe since 2015 is a very good example to address these environmental concerns [1]. Extensive research is underway at various parts of the world to meet environmental concerns by exploiting materials and composites prepared using renewable resources [2]. In this context, composites comprising polymer matrices and natural fibers are of great interest which can provide desirable properties and performance at affordable cost. Although natural fiber reinforced composites (NFRCs) show strong future potential and prospects, various materials and processing related challenges needs to be addressed to achieve long-term stability and performance. Currently, several synthetic polymers are being used as matrices to fabricate NFRCs, which find applications in automotive, electronic, packaging, construction and biomedical sectors [3]. Natural fibers in these composites provide several economic and environmental benefits as they are abundant, recyclable, biodegradable and more importantly they are relatively inexpensive than synthetic reinforcements such as glass fibers [3]. Recently there has been growing interest on thermoplastic-based NFRCs for high-performance engineering applications [2,3]. However, these non-biodegradable synthetic polymers pose significant disposal problems and therefore, complete environmental compatibility of NFRCs is still a great challenge. In this context, the best approach would be to produce NFRCs using biodegradable polymer matrices which are produced using non-renewable/renewable resources or current non-biodegradable polymers produced using renewable biological resources [4,5].

The present review manuscript examines the most essential phases in the developments of the inorganic class of environmentally benevolent Geopolymer concrete focusing on the valorisation of Waste of Glasses in context of incorporation in the manufacturing of Geopolymer concrete, especially concerning to its properties and applications. Their long-standing applications as structural materials developed through activation of alkali, i.e., Geopolymerization, in the field of sustainable constructions and infrastructures industries, diverse GPC are on the map. Even though, more advanced studies in the context of the said concept will be proved valuable to concerned industries people and of course, to the researchers themselves. Although the available literature in this innovation zone is few and far between, it breaks the surface, for the most of the centre of attention on its, incorporation with other waste materials pointing a finger to its approach to embrace ‘‘waste for the best” strategy. Previously, their character is neither wellfigured out nor aptly welcomed as in the ordinary Portland Cement based edifice materials enjoying. That is the core reason and objective of this article that review of its handy restricted literature to throw lights on the valorisation of blending of Waste of Glasses for the manufacturing of Geopolymer concrete centring its attributes and uses establishing it as a soon-to-be useful lucrative and sustainable global building material. The suggestions pointed out here in this manuscript will confidently be accommodating for potential research works on the topic. However, a modest challenge viz., curing complications, sometimes practical confronts of application, constrained supply chain, and a prerequisite for an observant directive of mix design for its fabricating, are standing up in its tracks to substitute Ordinary Portland Cement counterparts. Even so, when produced by utilizing vast and within reach precursors, activators and waste glass materials under up to the standard quality control of diverse characteristics, predominantly strength and green footprints of alkali activators, valorisation of Geopolymer concrete incorporated with waste glasses are momentous forthcoming part of the prospect toolbox of sustainable and economically reasonable construction materials. Eventually, the paper categorizes promotion of applications and most importantly the properties aspect for this promising novel type of building material.

Introduction

Concrete technology has witnessed a revolution since Romans era. Nowadays, a trend towards less energy-intensive, green, innovative, affordable, sustainable user-friendly building materials with low carbon footprint is the subject of attraction to researchers [1–4]. The application of diverse recycled solid waste is drawing the attention of engineers to incorporate them with construction composites. The market for recycled materials like concrete aggregates has been initiated through a project to develop it by Flemish Public Environmental Agency (OVAM) in 2006. It’s conclusion suggested that top-level recycled aggregates often finish up in substandard applications owing to the lack of certainty about the technical performances of recycled aggregates viz., consistency of properties, porosity, the presence of Chlorides, Sulphates, etc. and deficiency of regulations to encourage their applications with elevated added value [5].

1. Introduction

2. Self-Heating Methodology

3. Experimentation

4. Results and Discussion

5. Conclusion

Acknowledgements

Reference

The main objective of this paper is to present three indicators to determine the fatigue limit of woven carbon-fiber epoxy-matrix laminates using the Self-Heating test method. The approach adopted in the self-heating methodology consists usually in plotting the heat transfer indicator values versus the maximum stress values. This plot is named the self-heating curve and from the profile of the self-heating curve, one can identify the fatigue limit. During the self-heating experiments, the temperature of the specimen increases with the number of applied cycles and then stabilizes after a certain number of cycles. In this study a novel “peak-temperature point” approach was identified as the most suitable methodology to determine the fatigue limit for a class of composite materials. The paper also sheds some light on how a suitable approach can be chosen to uphold the economic aspect of the self-heating methodology. The purpose of the present paper is to validate this approach for an impacted laminate.

Introduction

CFRP structures have mostly replaced aluminium and steel, primarily due to their high strength and high stiffness to weight ratios, which are more than five times greater than conventional structural materials. Therefore, it is of utmost important for the scientific society to clearly understand the mechanical properties of these fibre reinforced composite materials, and especially the fatigue properties. CFRP composites are highly anisotropic and hence have complex failure mechanisms. Wöhler curves have been used to estimate the fatigue life of metals as well as composite materials [1-4]. The determination of the fatigue limit of materials is mostly time consuming and expensive. To have a quick determination of fatigue limit of materials, a quite new methodology named the SelfHeating methodology was adopted by several researchers for metals [5-9] and composites [10-11]. This methodology has been proven successful in evaluating the fatigue limit of unidirectional and woven CFRP materials without any inherent flaws. The fatigue experiments based on the self-heating methodology take only a couple of hours (maximum of one day) in comparison to the conventional fatigue tests which takes months to produce results.

Abstract

The aims of this paper are: (1) to review the current state of the art in the field of cartilage substitution and regeneration; (2) to examine the patented biomaterials being used in preclinical and clinical stages; (3) to explore the potential of polymeric hydrogels for these applications and the reasons that hinder their clinical success. The studies about hydrogels used as potential biomaterials selected for this review are divided into the two major trends in tissue engineering: (1) the use of cell-free biomaterials; and (2) the use of cell seeded biomaterials. Preparation techniques and resulting hydrogel properties are also reviewed. More recent proposals, based on the combination of different polymers and the hybridization process to improve the properties of these materials, are also reviewed. The combination of elements such as scaffolds (cellular solids), matrices (hydrogel-based), growth factors and mechanical stimuli is needed to optimize properties of the required materials in order to facilitate tissue formation, cartilage regeneration and final clinical application. Polymer combinations and hybrids are the most promising materials for this application. Hybrid scaffolds may maximize cell growth and local tissue integration by forming cartilage-like tissue with biomimetic features.

Introduction: Current Clinical Approaches and the Need for New Developments

The aim of this paper is to review the current state of the art of materials for cartilage substitution and regeneration. Section 1 describes the current state of the art in clinical treatments. Polymeric hydrogels used in cartilage regeneration and the reasons hindering their clinical success are reviewed in Section 2. The preparation techniques using polysaccharides and the resulting hydrogel properties are described in Section 3. Finally, future trends are explored in Section 4. Several reviews about hydrogels for cartilage regeneration have been published for the last 10 years, focusing on preparation and characterization, natural and synthetic polymer precursors, gelation kinetics, cell and drug delivery, growth factors, mechanical properties and biocompatibility. Nevertheless, most of those reviews do not propose new alternatives to improve hydrogels properties which can fulfill the real clinical needs in terms of tissue regeneration, mechanical properties and degradation kinetics. Therefore, this paper reviews relevant literature published during 2013–2017, related to the application, fabrication, characterization, in vitro and in vivo assays of biomaterials based on hydrogels for cartilage regeneration. The studies selected are articles and reviews written in English.

In many countries using nuclear energy high-level wastes resulting from the reprocessing of nuclear spent fuel is being confined in a highly-resistant glass matrix. In France, the resulting highly radioactive glass, named R7T7, is cooled in stainless steel canisters and stored on-site waiting for final geological disposal. For geological disposal the waste package will be encapsulated in carbon steel container and then sent to a multi-barrier underground disposal facility located in an argillaceous Callovo-Oxfordian (COx) layer. This confinement system should limit both the glass alteration by surrounding ground waters and the release of the radioactive elements from the glass matrix, although the alteration of the glass by surrounding ground waters cannot be excluded for long-term. It is expected after closure of the disposal facility that the glass will be firstly in contact with water vapour before complete saturation of the void spaces. In fact, the anoxic corrosion of metallic components will lead to a massive production of hydrogen that will probably prevent a fast saturation of the glass container with the surrounding ground waters. Consequently, a phenomenon of glass vapour hydration may occur for several thousands of years before the glass becomes completely submerged by groundwater. Various studies have been conducted to better understand the hydration of nuclear glasses [1−5] and their natural analogues such as obsidian [6−11]. During the hydration process, a thin film of water is firstly sorbed or condensed on the surface of the glass [12]. The thickness of the sorbed film of water mainly depends on the temperature and relative humidity (RH), the latter was controlled by varying the concentration of NaCl in the solution [13]. The condensed water diffuses and reacts via a hydrolysis and ion exchange mechanism. This leads to the transfer of glass components to the glass surface. The glass surface-area-to-liquid volume (S/V) ratio is estimated to be high under water vapour hydration (in the order of 108 m-1 ) [12]. This estimation is based on the sorption curve of water on the SRL glass as a function of the relative humidity. The thin film of water became rapidly saturated with dissolved glass constituents leading for certain glass compositions to higher local pH values and then the increase of solubility of the silicate glasses network. An alteration layer grows on the corroded glass surface; it is mainly composed of hydration gel, pore water and crystalline alteration products. The thickness of the alteration layer and the nature of secondary phases precipitated on the external surface depend on experimental conditions (time, temperature, RH, pH) and glass composition.