Self-Reinforced Polymer Composites

The Science, Engineering and Technology

Padmanabhan Krishnan, Sharan Chandran M

• Publisher: De Gruyter
• Year: 2022
• Print ISBN:
  9783110647297
• eBook ISBN:
  9783110647402
• Topic: Technology & Engineering
• Subtopic: Industrial & Technical Chemistry
• Index: Technology & Engineering

This book is a comprehensive introduction to all aspects of self-reinforced polymer composites (SRCs) science and technology. After introducing the fundamental characteristics of SRCs, ample space is given to manufacturing, processing, characterization and application techniques. The approach is didactic and focused on formulations, illustrations and applications, which makes the book ideal for students, teachers and practitioners alike.

Chapter 1 Introduction

1.1 Overview

The transportation industry is one of the most dynamic sectors in the world and is always pressurized to reduce fuel consumption and waste accumulation. Durable and recyclable parts, with improved fuel efficiency, are the strategic aim of transportation companies for the last few decades. Self-reinforced composites (SRC) are one of the milestones in the development of such materials. Both the matrix and the reinforced materials of SRCs are composed of materials from the same family. One such popular material developed in recent history is the carbon/carbon composite. Still, nowadays the term “SRC” has been widely used to streak polymer-based SRCs. SRCs are also referred to as one polymer composite, single polymer composite, all-polymer composite, or homopolymer composite in the review literature [1, 2, 3, 4, 5].

SRCs can be widely classified as polymeric types and nonpolymeric types as shown in Figure 1.1. Natural SRCs can be observed in nature. Wood cellulose and animal muscle are examples of natural SRCs. Some of the SRCs developed from renewable resources are used as biomaterials.

Figure 1.1: Classification of self-reinforced composites.

Self-reinforced polymer composites (SRPCs) can be beneficial to the industries that are dedicated to working for reduced impact on the environment. They possess improved chemical functionality compared to other traditional composites due to identical chemical structures. Lightweight materials are gaining attention, especially in air cargo, shipping, and transportation. SRPCs can be completely recycled by melting and result in zero waste accumulation. They indirectly help in gaining carbon credits by cutting the emission of carbon or greenhouse gases to the atmosphere.

Europe is one of the major manufacturers of composite materials. Production volume of glass fibre-reinforced plastics is observed to be at its highest level in 2019. This is an example of an increase in plastic waste accumulated in the environment.

The European parliament has voted to ban single-use plastic cutlery, cotton buds, straws and stirrers as part of a sweeping law against plastic waste that despoils beaches and pollutes oceans. The vote by MEPs paves the way for a ban on single-use plastics to come into force by 2021 in all EU member states. EU member states will have to introduce measures to reduce the use of plastic food containers and plastic lids for hot drinks. By 2025, plastic bottles should be made of 25% recycled content, and by 2029 90% of them should be recycled.

(The Guardian, 27 March 2019)

Similar regulations were implemented around the globe in the last few years. On 23 September 2019, India’s prime minister had assured the United Nations that India will lead the world in efforts to crap single-use polymers. India directly implemented BS-VI (Bharat stage VI – an emission control measure for automobiles) since April 2020 skipping stage V of Indian regulations for controlling emission of greenhouse gases from automobiles though this decision caused an economic slowdown in India a few months before COVID-19 lockdown. Concern over weight reduction to meet the tight environmental guidelines over fuel efficiency of aviation and automobile products was the trigger of the development of SRCs, recyclability being an added advantage. Reinforcing a matrix material with a lighter material may result in a composite material with weak properties. Reinforcing a material at least of the same family or compound will give rise to a better material without compromising other properties. The same family of materials is also expected to possess better chemical compatibility and hence an improved interfacial bonding.

Ceramic/ceramic SRCs and metal/metal SRCs are to be treated differently from polymer SRCs. It is hard to find out any noticeable work done in pure SRCs from ceramics or metals. They may be prepared from the compound of the same element and this similarity is helping in reinforcement. This reason may be taken as the criteria to classify them as SRCs. But it is more logical to classify them as pseudo-SRCs.

1.2 Ceramic/ceramic SRC

There are several composite materials composed of a common source of ceramic materials. They can be termed as ceramic self-reinforced materials. This session introduces some of the recent developments in ceramic SRCs which would be useful in gaining a brief idea about the family of SRCs. The development of such SRCs gained momentum just two decades ago. They may not contribute to the appreciable properties of SRPC as they are not recyclable or weight gainers. Still, some of the properties can be attributed to them by keeping SRPC as referent SRCs.

Ceramic SRCs differ from polymer SRCs right from the beginning of the processing procedure. Self-reinforcement in ceramic SRCs may be obtained by forming a multiphase microstructure with one of the phases forming the matrix and the second one as the reinforcement. It is also possible by heat treatment in which one of the phases will be precipitated to form the matrix phase. Growing elongated intertwined grains will also provide a self-reinforcement in some cases. Careful control of temperature plays an important role in ceramic SRCs just like in polymer SRCs. Additionally, control over the formation of microstructure becomes another characteristic feature in ceramic SRCs.

Silicon nitride ceramics are chemically inert and possess excellent high-temperature strength, low coefficient of thermal expansion, oxidation resistance, high creep resistance, and thermal shock resistance compared to other high-temperature structural materials. Still, covalent bonds in those materials make them difficult to sinter and increase manufacturing costs. It is not easy to fabricate complex-shaped components because of the covalent bond. Gas pressure sintering or hot pressing are used to dense silicon nitride ceramics. Pressureless sintering is a method to overcome the issues in manufacturing. In situ self-reinforced textured microstructure can be produced by a combination of seeding, anisotropic grain growth and shear forming processes [6].

Although the preparation of silicon nitride was first reported in 1857, self-reinforcement researches in silicon nitride were developed only in the last two decades. Si₃N₄ is used in many applications like auto turbochargers, diesel engines, hydraulic pumps, bearings, spinal fusion devices replacing titanium, and polyether ether ketone. Matrix material like Ba₂Al₂Si₂O₈ (barium aluminosilicate, BAS) is poor in mechanical properties, and structural applications are limited. When BAS was reinforced with silicon nitride (Si₃N₄) by various processes like sintering, the resulting composite was a pseudo-SRC of silicon [7]. A promising class of materials with various structural applications including aerospace are being developed.

1.3 Metal/metal SRC

There is no universally accepted definition for a composite material. While defining and classifying SRCs, the same dilemma exists. However, the materials are classified as composites based on their load transferability from matrix to the reinforcement. Reinforcement need not be a material added from outside as we have seen in previous examples. Sometimes, the load-carrying ability of metals is improved by hindering the dislocation motion with small particles by dispersion or precipitation.

Pseudo-SRCs of discontinuously reinforced titanium matrix composites are gaining attention at a faster pace due to their wide acceptance in the automobile, aerospace, and aviation industries. They possess high specific strength, high-temperature resistance properties, and corrosion resistance. Thermal expansion coefficient is an important property to be considered for the materials used in high-temperature applications. Titanium boride (TiB) whisker is one of the suitable reinforcements in this regard for titanium matrices as it also possesses high elastic modulus and better interfacial bonding with titanium matrix. In TiB-reinforced Ti, an interfacial layer of TiB was formed by the precipitation of boron into the matrix as needles on the grain boundaries [8]. Another example in titanium-based composites is the development of research in coatings of titanium composites. TiB and TiC particles reinforced on Ti₆Al₄V by laser cladding using Ti-B₄C-Al or Ti-B₄C-C-Al powders as the precursor materials also fall under the category of SRCs [9].

1.4 Carbon/carbon SRC or all carbon composites

Carbon fibres were used by Thomas Edison as filaments of light bulbs in 1800. Industrial development of carbon fibres began in 1886 when National Carbon Company was established in Cleveland, Ohio [10]. Properties of carbon fibres improved later over two centuries and these fibres became one of the key materials in high-temperature, low coefficient of thermal expansion applications. Composite materials developed with carbon fibres as reinforcement offered a wide range of application options with improved mechanical properties [11].

Carbon exists in a variety of forms like graphite, diamond, graphene, fullerene, and carbon nanotubes. Graphite and fullerene are the allotropic forms of carbon widely used in carbon/carbon composites. The major limitation of carbon is its reaction with oxygen and the release of gaseous oxides of carbon. These composites were developed for space applications and jet vanes, used in German V₂ rockets in the beginning and later has got wide acceptance. They are also used in brake disk systems in racing cars, aircraft brake systems, and so on.

There are various processing routes for carbon/carbon composites. Sintering is not a possible way of processing these types of composites. Carbon matrix in a carbon/carbon composite is obtained generally by chemical vapour deposition of carbon or thermal decomposition of pitch or phenolic resin. However, the resulting composite will not possess the required density and strength due to the presence of pores.

High-pressure impregnation carbonization is one of the methods to fabricate carbon/carbon composites. A woven carbon fabric is impregnated with thermoplastic pitch under heat and pressure followed by pyrolysis of the pitch into carbon. Polymer matrix composites reinforced with carbon fibres can be converted to carbon matrix composites by converting the polymer into carbon by pyrolysis. In liquid-phase impregnation process, coal/tar/petroleum pitches and high carbon-yielding pitches are impregnated in the carbon fibre architecture.

Mechanical properties like strength-to-weight ratio and specific stiffness are high in carbon/carbon composites that are five times lighter than steel and two times lighter than aluminium. They are stable even above 3,000 °C with negligible thermal expansion when coated with thermal materials. They offer excellent fatigue properties and resistance t...

Table of contents

• Title Page
• Copyright
• Contents
• Chapter 1 Introduction
• Chapter 2 Raw materials
• Chapter 3 Polymer self-reinforced composites – a review
• Chapter 4 Carbon/carbon and ceramic self-reinforced composites
• Chapter 5 Processing and manufacturing self-reinforced polymer composites
• Chapter 6 Characterization of self-reinforced polymer composites
• Chapter 7 Interfacial mechanics of self-reinforced polymer composites
• Chapter 8 Performance of self-reinforced polymer composites
• Chapter 9 Experimental fracture and failure analysis in SRCs
• Chapter 10 Self-reinforced polymer composites – global solutions and technological challenges!
• Index