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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Serie: Polymer Science and Plastics Engineering
- Sprache: Englisch
“Plastics Additives and Testing” is a practical book for engineers and operators and discusses both inorganic and organic chemicals that are widely used as additives in plastics processing operations.
It is common practice today to use analytical techniques to improve plastics processing. Because it is critically important to manufacture quality products, a reasonable balance must be drawn between control requirements and parameters for improved processing method with respect to plastics additives. This book serves to implement this balance in the manufacturing line.
Written by a successful, international consultant with an excellent publishing track record, it combines plastics additives, testing and quality control and is a valuable and critical book for engineers and operators to have when performing their tasks.
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Seitenzahl: 313
Veröffentlichungsjahr: 2013
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Contents
Cover
Half Title page
Title page
Copyright page
Preface
Chapter 1: Introduction
1.1 Summary
References
Chapter 2: Thermoplastics and Thermosets
2.1 Benefits/Advantages of Plastics
2.2 Classification
2.3 Thermoplastics
2.4 Thermosets
References
Chapter 3: Types of Additives
3.1 Selection of Additives
3.2 Surface Property Modifiers
3.3 Chemical Property Modifiers
3.4 Processing Modifiers
3.5 Mechanical Property Modifiers
3.6 Aesthetic Property Modifiers
3.7 Other Additives
3.8 Additives from Natural Sources
References
Chapter 4: Plastics Additive and Chemistry
4.1 Properties of Plastics
4.2 Chemistry of Additives
4.3 Chemical Properties of Additives
References
Chapter 5: Organic Additives
5.1 Antioxidants
5.2 Antistatic Agents
5.3 Antifogging Agents
5.4 Antiblocking Agents
5.5 Slip Additives
5.6 UV Stabilizers
5.7 Nucleating Agents
5.8 Flame Retardants
5.9 Lubricants
5.10 Plasticizers
5.11 Impact Modifiers
5.12 Fillers
5.13 Organic Colorants
5.14 Foaming Agents
5.15 Chain Extenders
5.16 Organic Peroxides
5.17 Accelerators
5.18 Activators
References
Chapter 6: Inorganic Additives
6.1 Heat Stabilizers
6.2 Flame Retardants
6.3 Fillers
6.4 Blowing Agents
6.5 Inorganic Colorants
6.6 Antimicrobial Agents
References
Chapter 7: Additives and Processing
7.1 Plastics Processing
7.2 Nature of Plastics
7.3 Nature of Additives
7.4 Plastics Processing Technology
7.5 Injection Molding
7.6 Extrusion
7.7 Blow Molding
7.8 Thermoforming
7.9 Role of Additive
7.10 Rotational Molding
7.11 Calendering
7.12 Thermosets and Processing
References
Chapter 8: Identification of Additives
8.1 Melting and Boiling Point
8.2 Organic Additives
8.3 Inorganic Additives
8.4 Morphology
8.5 Mass Spectrometry
8.6 Scanning Electron Microscopy (SEM)
8.7 Benefits
References
Chapter 9: Testing of Additives
9.1 Plastics and Additives in Analysis
9.2 Properties of Additives
9.3 Testing of Additives
9.4 Brabender Plastographs
9.5 Extraction of Polymer Additives Systems
9.6 Liquid Chromatography
9.7 Gas Chromatography
9.8 Thermal Analysis
9.9 Thermogravimetric-Mass Spectrometry
9.10 FTIR Spectroscopy
9.11 Quantitative Analysis of Additives
9.12 Quality Control
References
Chapter 10: Future Trends
10.1 In Plastics Packaging
10.2 In Medicine
10.3 In Electrical and Electronics Industries
10.4 In Building
10.5 In Engineering
10.6 Present Trends
10.7 Future Requirements
References
Index
Plastics Additives and Testing
Scrivener Publishing 3 Winter Street, Suite 3 Salem, MA 01970
Publishers at Scrivener Martin Scrivener ([email protected]) Phillip Carmical ([email protected])
Copyright © 2013 by Scrivener Publishing LLC. All rights reserved.
Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts.Published simultaneously in Canada.
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Library of Congress Cataloging-in-Publication Data:
ISBN 978-1-118-11890-0
Preface
Pioneers of additives realized that their chemistry offers multiple advantages for use in plastics. Various findings regarding additives and their applications, have led to tremendous growth as reflected by their usage in plastics processing and end-product applications. Embarking on a new millennium, there is need for more plastics additives and testing.
Plastics Additives and Testing is essential for both R&D laboratories as well as for use in quality control. It is particularly useful in introducing standard additive testing techniques to technicians and engineers beginning their careers in plastics processing, testing and product development. A major part of the book is comprised of additives and testing and is intended to provide the reader with a practical source of fundamental information.
Also provided in this book is an overview of plastics additives and testing methods useful to researchers, product development specialists, and quality control experts in plastics processing. Engineers, polymer scientists and technicians will find this volume useful in selecting additives and testing applicable processing and characterization. It is my sincere hope that this book will benefit both new and experienced plastics technologists and processors in their efforts to improve the art and science of plastics additives.
This book is intended to be a practical guide for achieving optimal processing and product performance. With an emphasis on developments in plastics additives and testing, it presents a comprehensive overview of the various facets, scope and limitations of additives in plastics. The author thanks Mrs. Himachalaganga for her assistance in editing the chapters, and particularly for the testing of additives, and Venkatasubramanian and Sailesh for their assistance in typing the chapters. I am grateful to my distinguished professors who encouraged me to write a book that would be an effective reference. The author wishes to extend gratitude to his guide, Dr. A. Thamaraichelvan, Principal, Thiagarajar College, Madurai, and above all to the almighty who provides enough health and knowledge.
Muralisrinivasan Natamai SubramanianMadurai
Chapter 1
Introduction
The chain reactions of small molecules called monomers result in macromolecular substances depending on their molar mass which are called oligomers or high polymers. The utility of the properties of polymeric materials depends on
molecular characteristics of comprising macromolecules;
arrangement of macromolecules in the system;
nature and amount of additives—may be low or high molecular substances in liquid or solid state.
These polymers and additives are together called plastics. The primary molecular characteristics of plastics are molar mass, chemical structure (composition) and physical architecture [1]. Plastics are the world’s fastest growing family for good reason, namely
their economy and performance;
their easy processing.
Surface structures and behavior of plastics affect many crucial properties which include friction, abrasion, wetting, adhesion, penetration and adsorption phenomena. These properties greatly control engineering and surface and are of utmost importance in processing and applications. They also govern transport properties, hence, additives play an important role [1].
Plastics are high molecular weight and have a wide range of mechanical and physical properties. Modern plastics have been seen in a very large range of commercial applications in both industrial as well as consumer products. Plastics have properties such as low density, high strength to weight ratio, good barrier resistance, and readiness to manufacture using a range of processes [2]. However, plastics are intrinsically difficult to process.
Many plastics would simply be of limited use without additives. For successful plastics processing and products, additives are frequently used for a variety of reasons. Numerous products are routinely fabricated with processing technology. This is made possible by the addition of additives to plastics to manufacture commercial-type products. Additives are often combined with plastics through dispersal.
Additives can be defined as a chemical substance which can be put into the polymer in a form in which it is effective, and which will remain long enough to be able to exert its influencing action in processing and the end products life. It is useful to examine solubility in determining additive compatibility. A completely insoluble additive is unlikely to be effective, and therefore solubility is the most important factor in additive compatibility [3].
Additives play an important leading role in the conversion of plastics into products. They enable a cost effective fabrication of mass products such as profile, pipe, and molded products. Plastics and additives are primarily used in melt-mixing procedures to influence processing by injection molding, thermoforming, extrusion, etc.
Additives are chemical compounds used to enhance the life and properties of plastics. They are not chemically bonded, but mechanically dispersed in polymers [4]. The additives used by the plastics industry are sometimes chemically complex compared to the common solvents. Some of them are polymorphous materials. The performance of additives is strongly affected during processing by their thermal history [5].
Plastics tend to undergo degradation during their processing and service life [6]. However, the stability of the plastics depends upon its structure, method of manufacture, and catalyst residues left behind after the polymerization. The use of additives is dependent on the application and nature of the plastics. Additives can improve the plastics processing conditions by modifying a wide range of characteristics. Since most processing technologies in the modern plastics industry involve hot melt flow, the influence of additives on the rheological properties of molten plastics is of great importance from both the scientific and engineering point of view [7]. However, plastics additives have been hindered by a lack of fundamental understanding.
Customarily additives are added to plastics after polymerization in a step involving mechanical mixing. Therefore, plastics usually contain several additives which are included in the formulation to impart certain desired properties either during processing or subsequently. The effectiveness of additives depends primarily on their ability to interfere with the chemistry either by virtue of chemical reaction or by physical processes. The inherent efficiency of many modern additives is that they are capable of being introduced into the polymer in a form which is active, and can remain in the polymer long enough for their potential effect to be realized.
With technological progress, the introduction of additives to plastics has been based on a matter of trial and error experimentation [8]. The understanding and testing of plastics additives could also be useful during processing as well as end products in service. An accurate and rapid determination of additives is essential for the grading of the product. Methods such as ultraviolet and infrared spectroscopic determination of the samples are routinely used for quality control. However, such methods are not very helpful when additives such as antioxidant and UV stabilizers, or two antioxidants with overlapping frequencies in UV and IR spectrum, are present in the plastics [9].
The need for more powerful analytical techniques has grown exponentially over the last decade to meet the high complexity of polymers and additives. The increased demand for specific required information has become ever more evident in order to achieve the desired level of accuracy and reliability of analytical data. The analysis of plastics and additives requires the combination of powerful separation techniques with sensitive detection [10].
From the laboratory bench tests, performance tests on additives, and practical application in the industry, there appears to be a wide field of utilization in applications where improvements in properties are either mandatory or desirable. Additives with pronounced chemical properties combined with physical parameters such as appearance, melting or boiling point, etc., are a valuable addition to plastics for processing and improving physical and chemical properties. However, a rapid and accurate method of determining these additives in plastics is needed to control their application in the manufacturing process and in research operations.
1.1 Summary
Additives are simple chemical compounds, sometimes chemically complex.
Without the addition of additives, plastics processing is very difficult.
Additives disperse in plastics and are not chemically bonded. Hence, additives in plastics are mostly a physical mixture.
Additives are added in small concentrations.
Additives influence the rheological properties of the plastics melt during processing.
References
1. E. Yilgor, I. Yilgor, and S. Suzer. Polymer (2003) 44, 271.
2. C.P.J. O’Connor, P.J. Martin, and G. Menary. Int. J. Mater. Form (2010) 3, 1, 599–602.
3. P.D. Calvert, and N.C. Billingham. Journal of Applied Polymer Science (1979) Vol. 24, 357–370 (1979).
4. M.M. Hirschler. In Developments in polymer stabilization-5, G. Scott, ed., Applied Science Publisher, London, (1982) 107–53.
5. Enikö Földes. Die Angewandte Makromolekulare Chemie (1998), 261/262, 65–76.
6. H.J. Heller. Eur. Polym. J. Suppl. (1969) 105.
7. F. Suhara, and S.K.N. Kutty. Polym. Plast. Technol. Eng. (1998), 37, 57.
8. H.-J. Lee, and L.A. Archer. Macromolecules (2001), 34, 4572.
9. V.C. Francis, Y.N. Sharma, and I.S. Bhardwaj. Die Angewandte Makromolekulare Chemie (1983) 113 219–225.
10. M.P Thomas. J. Vinyl and Additive Tech. (1996) 2, 4, 331–338.
Chapter 2
Thermoplastics and Thermosets
The majority of plastics are made from petrochemical resources, a nonrenewable resource [1–3]. Over the years, plastics production has been growing rapidly in many applications. Plastics are present everywhere in different areas of daily life for the convenience of the modern consumer. Also, they are used in areas such as the transportation, construction, appliance, and electronics industries.
2.1 Benefits/Advantages of Plastics
Plastics have replaced materials such as glass, metals, paper, wood and masonry in recent times. The growth in the use of plastic is due to its beneficial properties, which include [4]:
Ease of processing and energy efficiency
Resistance to microbial attack
Extreme versatility and ability to be tailored to meet specific technical needs
Lighter weight than competing materials reducing fuel consumption during transportation
Good safety and hygiene properties for food packaging
Durability and longevity
Resistance to water and chemicals
Excellent impact, thermal, electrical insulation and optical properties
Comparative lesser production cost
Unique ability to combine with other materials like aluminum, foil, paper, adhesives
Far superior aesthetic appeal
Material of choice—human life style and plastics are inseparable
Intelligent features, smart materials and smart systems
Less susceptible to breakage
The molecular weight (MW) and molecular weight distribution (MWD) are important factors in determining the mechanical and rheological properties of polymers. It is believed that the polymer fraction of low MW improves the flow properties, while the fraction of high MW enhances melt strength and good mechanical properties. Therefore polymers with bimodal MWD may simultaneously show enhanced mechanical and rheological properties [5].
In 1986, 75% of the 22 million tons of plastics were converted to long-life applications, out of which 25% were utilized in packaging and other short-life uses [6] with additive consumption of 500,000 tons of additives utilized in it. Additives aid the manufacture of articles of various colors, completed shapes and designs [7, 8]. Without additives, no one can imagine the feasibility of the processing and end use of products made from plastics. Plastics additives in the 32 billion US dollar market is expected to grow [9] every year at least not less than 2%. About 85% of additives are consumed only by the PVC market [10]. Plasticizers are considered to be about 58% of the market among plastics additives. A majority of plasticizers are used for flexible PVC manufacturing [11]. The common plastics have increased in use much faster than the economy has expanded. The growth promises to continue above the rate of the gross national product (GNP)—unless limited by hydrocarbon feedstock availability—since this energy-resource question distorts all projections today [12].
2.2 Classification
On the basis of thermal behavior, polymers can be divided into two major types:
Between thermoset and thermoplastic polymers, the latter has found more and more applications in the last three decades. This is due mainly to their ability to be reprocessed upon processing.
2.3 Thermoplastics
Thermoplastics are used in many applications because of their lightweight, economic fabrication and good chemical resistance [14]. The dependence of the specific volume of thermoplastics on the temperature and on the pressure results in significant local volumetric changes in the thermoplastic as it cools during processing [15].
The most important property of a thermoplastic with regard to specification of the processing conditions is its viscosity. The viscosity of even a thermoplastic varies with temperature and may also vary with the feed rate and local flow geometry [16].
Thermoplastics are classified into three major classes [17]:
2.3.1 Polyolefins
Polyolefins are the second largest material used in numerous fields of applications throughout the world. The double-bond characteristic of the alkene series with non-polar backbone is known by the term polyolefins. Polyethylene and polypropylene are the major members and widely used class of polymers known as polyolefins [18]. Polyolefins are used on a large scale as packaging material around the world. Polyolefins have received considerable attention for their improvement in the durability of the polymers.
Polyolefins were revolutionized due to the discovery of metallocene-based catalysts during the 1980s. The catalyst based on metallloncene controls the stereoregularity and molecular mass in chain structure [19–21]. Polyolefins as a single polymer [22–26] without additives have not proven ideal for their oxygen and water barrier performance features essential for long shelf-life materials. The additives usage improves the mechanical and barrier properties in polyolefins in many specific applications.
2.3.1.1 Polyethylene
Polyethylene (PE) is the most important polymer which covers the largest percentage of the plastic family. The molecular chain of PE is composed of–CH2–[27–28]. Polyethylene comes in many forms—high density, low density, linear, hyperbranched [29–30]. Polyethylenes differ in their densities, types and extents of branching, and types and amounts of double bonds, depending on the polymerization process used commercially [31–32]. The linear low density polyethylene represents one of the members of this family with broad use. Table 2.1 indicates some of the physical properties of PE.
Table 2.1 Typical properties of polyethylene.
Polyethylene is usually synthesized from low pressure and catalytic processes with temperature [38–39]. It is also synthesized from high temperature (above 200°C) and pressure (greater than 1000 bar), a high energy consuming free-radical process [40–41]. In the high temperature process, a branched, low density, polyethylene is produced. Ziegler-Natta catalysis enables the synthesis of high density polyethylene with high crystallinity and melting temperatures. For slurry polymerization, a new catalyst compatible with green diluents such as supercritical CO2 [42–44] or water [45–18] have been developed. PE started to degrade yet showed very low volatility levels under 360°C. As the temperature was raised above 360°C, the degradation rate increased quickly and a quantity of volatile, seldom monomer-type compounds, was produced [49].
Polyethylenes differ in their densities, types, extents of branching, amount of double bonds, and the polymerization process used commercially. Linear low density polyethylene (LLDPE) mainly includes Ziegler and metallocene types of polyethylenes. Polyethylene (PE) is a common synthetic polymer with high molecular weight and hydrophobic level. It is nondegradable in nature [34, 50–51]. A pure polyethylene is quite stable and gives off fairly innocuous low molecular weight hydrocarbons upon degradation.
Polyethylene is the most attractive thermoplastic for making the natural-fiber plastic composites. It is used mainly as the exterior building components [52]. Polyethylene is an inert polymer with good resistance to microorganisms. However, that fungal growth can occur on the surface of polyethylene [53–54]. Polyethylene is used to manufacture everything from plastic bags and bottles to huge gas pipes [55].
2.3.1.2 Polypropylene (PP)
PP is composed of linear hydrocarbon chains. The properties resemble PE in many respects. It has good surface hardness, resistance to scratches and abrasions, and excellent electrical properties. The consumption of polypropylene has increased globally due to its low density, high vicat softening point, good flex life, and sterilizability. Table 2.2 illustrates some of the physical properties of polypropylene.
Table 2.2 Typical properties of polypropylene.
The inertness of polypropylene toward chemicals excludes its use in industrial applications such as dyeing of fibers, printing of films, paintability, adhesion, etc. [56–57]. Polypropylene homopolymer is not a tough material at low temperatures [58–59]. Polypropylene is a highly crystallizable, low cost and balance-strength polymer. It has potential applications in the area of composite fabrications, and in some cases, as a replacement for low-end-use engineering polymers [60–61]. However, the application of PP in some technologically important fields seems to be limited due to its lack of polar functional groups, as well as its inherent incompatibility with additives and other polar polymers [62–65].
2.3.2 Polystyrene
Polystyrene (PS) is a semi-crystalline polymer characterized by strong chemical resistance, good electrical insulating properties, low melt viscosity, excellent dimensional stability, and low moisture absorption [68–69]. Neat and glass-filled syndiotactic polystyrenes are used in automotive, electrical, and industrial parts. Table 2.3 illustrates some of the physical properties of polystyrene.
Table 2.3 Typical properties of polystyrene.
Polystyrene has
good clarity and sparkle;
excellent stiffness, enabling down gauging;
no taste and odor transfer so critical to sensitive food products;
forms easily with good definition.
Polystyrene is quite stable, except in regards to light. Ketones, aromatic and chlorinated hydrocarbons will dissolve or swell polystyrene, and it is subject to degradation in the presence of acid pollutants. Acids and alcohols will adversely affect polystyrene. Oils, low-molecular-weight alcohols and hydrocarbons, as well as solvents, can aggravate stress cracking [27, 28].
2.3.3 Polyvinylchloride (PVC)
Polyvinylchloride (PVC) is linear and thermoplastic in nature. It is a substantially amorphous polymer. It is of huge commercial interest due to its physical and mechanical properties [72]. With respect to the production and consumption of synthetic materials, it stands third in the world after polyethylene and polypropylene [73–75].
Polyvinylchloride is widely used in electrical insulators, and for plastic moldings and building materials. Table 2.4 illustrates the typical properties of PVC.
Table 2.4 Typical properties of PVC.
Polyvinylchloride makes commercial products difficult to process due to its poor thermal stability [81]. It also has a photodegradation problem which prevents it from being of great importance for widespread PVC usage. However, its properties can be easily modified by the use of suitable additives. PVC has no absorbance at 230–450 nm [82]. PVC is a multifunctional system comprised of stabilizers, modifiers, processing aids, lubricants, and fillers [81].
2.3.4 Acrylonitrile-Butadiene-Styrene (ABS)
Acrylonitrile-butadiene-styrene is one of the Post-war materials available since 1948. ABS is usually opaque, although translucent moldings may be found. ABS is a thermoplastic, and thus easily molded into durable items such as telephone housings, football helmets, toys and luggage [83]. It is widely used as an engineering thermoplastic with good mechanical behavior and chemical resistance.
The acrylonitrile-butadiene-styrene (ABS) polymers are based on three monomers: acrylonitrile, butadiene and styrene. Because of its good balance of properties, toughness/strength/temperature resistance coupled with its ease of molding and high quality surface finish, ABS has a very wide range of applications. ABS is widely used as an engineering thermoplastic. It also possesses good mechanical behavior and chemical resistance [84].
Applications of ABS include electrical and electronic equipment (EEE), automobiles, communication instruments, and other commodities. The butadiene segment of the molecule is elastic, thus allowing the material to absorb shock without harm. Table 2.5 illustrates typical properties of ABS.
Table 2.5 Typical properties of ABS.
Acrylonitrile, butadiene and styrene are terpolymers widely valued for their strength and toughness. ABS is widely used as an engineering thermoplastic with good mechanical behavior and chemical resistance. After periods of exposure to heat and oxygen, the mechanical properties of ABS, such as impact strength and elongation-to-break, deteriorate as a consequence of this polymer degradation, inducing premature failure [87]. The durability of ABS polymers is important in many applications and is dependent on composition, processing and operating conditions, environmental weathering, heat aging and installation damage.
2.3.5 Poly(methyl methacrylate) (PMMA)
Poly(methyl methacrylate) (PMMA) is a typical transparent amorphous polymer and has been widely used as an important material for optical devices. PMMA is a hard, rigid material with high glass transition temperature. Polymers become softer and more flexible (Tg decreases) with the increase of the length of the side ester chain up to certain limit. PMMA has several advantages such as good flexibility, high strength and excellent dimensional stability. However, it suffers from shortcomings such as poor heat resistance, weak mechanical surface, low refractive index, etc. [88–89]. Table 2.6 illustrates typical properties of PMMA.
Table 2.6 Typical properties of PMMA.
PMMA is light weight and has good mechanical and electrical properties, great resistance to high temperature, aging and chemicals, and easy formability [93–94]. This amorphous, transparent material is best known for its clarity (about 92%). It has good weatherabilty, UV resistance, high rigidity and good impact strength. PMMA is widely used in adhesives, automotive signal lights, lenses, light fittings, medallions, neon signs and protective coatings because of its excellent optical (clarity), physical and mechanical (dimensional stability with high modulus) properties.
2.3.6 Polyesters
Polyesters are one of the most versatile classes of polymers ever produced. Nowadays, they are one of the most promising alternatives to commodity plastics [95]. As fiber, bottle, and film material, or as matrix for glass-reinforced plastics, they have found a wide field of application. They are distinguished by their very good processability, low shrinkage, low water content and barrier properties. Limitations arise from their relatively low glass transition temperatures resulting in reduced thermal stability. To overcome this problem polyesters are often reinforced by glass fibers and/or crosslinked by various methods. Such materials are being used in electrical applications [96].
Polyester refers to many ester groups present in the polymer molecule. It is used not only in the field of thermoplastics, but also as thermosetting plastics. The low melting points of aliphatic polyesters have prevented their wide usage as polymeric materials for a long time. However, because of their characteristic biodegradability and ongoing environmental concerns, aliphatic polyesters are now in the spotlight [97].
The majority of polyesters are unstable and subject to hydrolysis at elevated temperatures. However, some chemical resistant polyesters are also available. Many polyesters have poor water resistance and are affected by most solvents. Alkalis will decompose polyesters and phenol adversely affects them. They yellow on exposure to light. Various organic acids are emitted upon degradation [83].
Among polyesters, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) are thermoplastic engineering materials of large commercial importance due to their outstanding physical and mechanical properties such as high strength, stiffness, toughness and heat resistance [98]. Hence, the aromatic polyesters PET and PBT have taken on a central role in engineering plastics. Two particular thermoplastic polyesters are of importance.
2.3.6.1 Poly(ethylene terephthalate) (PET)
Poly(ethylene terephthalate) (PET) is a widely used engineering plastic used in applications such as soft drink bottles. PET was originally introduced as a fiber-forming material. It is the highest-volume polyester produced and is used in numerous applications such as films, fibers, and packaging [98–99]. Table 2.7 illustrates typical properties of PET.
Table 2.7 Typical properties of PET.
PET is also used in injection molding as a material of great importance for disposable bottles due to its transparency, thermal stability, chemical resistance, and excellent barrier properties. It is also used in packaging of food, dairy products, etc., which has led to growth in the PET market [83]. It is distinguished by its good processability, low shrinkage, low water absorption and barrier properties [96]. However, there is still much debate as to the exact mechanism of the changes which take place during orientation processes and the formation of three-dimensional order.
2.3.6.2 Polybutylene Terephthalate (PBT)
Poly(butylene terephthalate) (PBT) is one of the engineering thermoplastic polyesters that offers excellent performance for a variety of applications [102–108]. PBT, also known as polytetramethylene terephthalate (PTMT), is usually used in glass-fiber-filled form to give a rigid material with excellent dimensional stability, particularly in water, that is resistant to hydrocarbon oils without showing stress cracking. Table 2.8 illustrates some of the typical properties of PBT.
Table 2.8 Typical properties of PBT.
PBT is mainly used as an insulator in the electrical and electronics industries. Compared to PET, PBT has lower strength and rigidity, better impact resistance, and a lower glass transition temperature [98–99].
2.3.7 Nylons
Nylons (polyamides) are one of the most widely used engineering thermoplastics [111–115]. However, limitations in mechanical properties, low heat distortion temperature, high water absorption, and dimension instability of pure nylons, have prevented their applications in structural components. Table 2.9 illustrates some of the physical properties of nylon.
Table 2.9 Typical properties of Nylon.
Polyamides are widely used thermoplastic polymers for structural applications [14, 116–119]. Nylon is an engineering thermoplastic, commercially made by anionic ring opening polymeriation of caprolactam. It is used in the filaments of tooth-brushes, ropes and the filaments for garments like raincoats, and is also used in the automobile industry for self-lubricating gears and bearings.
Nylon 6 has high mechanical strength and better resistance to elevated temperature. Nylon is a protein-like, man-made synthetic material. The presence of the amide group along the backbone of the nylon results in inter- and intramolecular hydrogen bonding, and influences chemical and physical properties [120]. However, the inter- and intra-chain interactions are not fully understood. Since 1938, nylon has been widely used in applications which include textile fibers, industrial cards and in engineering applications. It is also used in producing carpets, plastic gears and bushings, electric parts, fishing lines and ropes.
Even though water is absorbed more effectively by solutions of acids and alkalis, nylon tubes should prove very suitable for the conveyance of many organic solvents. Generally nylon is soluble in formic acid and phenol. Acids and alkalis may cause hydrolysis.
Exposure of aliphatic polyamides (nylons) to the environment causes discoloration and appreciable reduction in tensile strength and average molecular weight. Since the polyamide itself can absorb short-wavelength solar UV radiation, dual mechanisms of degradation initiated by sunlight have been identified in the aliphatic polyamides [121–122].
2.3.8 Polycarbonate
Polycarbonate (PC) is a commercially important engineering thermoplastic that possesses several distinct properties including transparency, dimensional stability, flame resistance, high heat distortion temperature, high impact strength and moisture insensitivity [123–128]. It can be widely used in applications that require transparency and impact resistance including windshields, canopies, vision blocks, face shields, goggles and lenses [129]. There is considerable interest in improving the mechanical properties of PCs while maintaining transparency. Several approaches have been investigated to improve the mechanical performance of PC, including the addition of small amounts of core-shell impact modifier [130], short glass fiber [131–132], inorganic whiskers such as aluminum borate whiskers [125], potassium titanate whiskers [124], carbon nanotube or nanofiber [133–138], polyhedral oligomeric silsequioxane (POSS) [139], organoclay [140–143], atomic layer deposited alumina films on PC substrate [144] or polycarbonate layered-silicate nanocomposite [145]. Researchers saw improved tensile properties but often at the expense of transparency [146–148]. Table 2.10 illustrates some of the physical properties of PC.
Table 2.10 Typical properties of PC.
PC is bisphenol-A-based polyester, which is an important engineering thermoplastic having unique properties such as transparency, toughness, thermal stability and dimensional stability. These properties make it useful for many applications such as compact discs, riot shields, vandal-proof glazing, baby feeding bottles, electrical components, safety helmets and headlamp lenses.
Polycarbonate has an attractive combination of mechanical properties and good heat stability. Processing is carried out at rather high temperatures in order to decrease the high melt viscosity characteristic of the polycarbonate [149].
2.3.9 Polyoxymethylene (POM)
Polyoxymethylene (POM) is one of the typical engineering plastics with a high crystallinity. The crystalline nature is important for POM, and it brings a high modulus as well as a good dimensional stability [150]. Typical properties of polyoxymethylene is illustrated in Table 2.11 above.
Table 2.11 Typical properties of POM.
It possesses strength and rigidity approaching those of nonferrous metals [155–156]. They are hard, strong, and highly crystalline thermoplastics with a unique balance of mechanical, thermal, chemical, and electrical properties. POM resins exhibit good self-lubricating property and wear resistance [157–159]. Consequently, they are widely applied as the rotational materials of mechanical and electromechanical components of electronic parts, automotives, precision instruments, etc.
2.3.10 Biodegradable Plastics
Biodegradable plastics are polymer species. Biodegradable plastics that are compostable can be treated biologically together with other biowaste. Biodegradable plastics whose components are derived from renewable raw materials can be made from abundant agricultural/animal resources like cellulose, starch, collagen, casein, soy protein polyesters and triglycerides. Biodegradable plastics degrade over a period of time if exposed to sun and air [160].
Biodegradable plastics have an expanding range of potential applications, and they are environmentally friendly. Therefore, there is growing interest in degradable plastics which degrade more rapidly than conventional disposables. The biodegradability of plastics is dependent on the chemical structure of the material and on the constitution of the final product. Therefore, biodegradable plastics can be based on natural or synthetic resins. Natural biodegradable plastics are based primarily on renewable resources and can be either naturally produced or synthesized from renewable resources. Biodegredation is degradation caused by biological activity, particularly by enzyme action leading to significant changes in the materials’ chemical structure. As any marketable plastic product must meet the performance requirements of its intended function, many natural biodegradable plastics are blended with synthetic polymers to produce plastics that meet these functional requirements [161].
Biodegradable polymers with a controllable lifetime are becoming important [162–163]. Bioplastics constitute an emerging and innovative industrial segment characterized by new synergies and collaborations among the chemical, biotechnological, agricultural, and consumer sectors. Bioplastics therefore are defined as materials that contain biopolymers in various percentages and that can be molded by heat action and pressure. They are thus potential alternatives to conventional thermoplastic polymers of petrochemical origin, such as polyolefins and polyesters.
Biopolymers can be grouped into the three classes given below:
Although these polymers have been used extensively as sutures, implant materials, and drug carriers, they do not have any inherent biological functions to actively participate in human body repair. These aliphatic polyesters are not “biologically active” and cannot exert biological activity directly. They only play a passive role in wound healing, tissue regeneration, and tissue engineering. It would be ideal to make these biomaterials biologically “alive” and perform some critical biological function, such as the ability to modulate inflammatory reactions to facilitate wound healing or to enhance host defenses against disease [169].
2.4 Thermosets
Thermosetting resins, or thermosets, play an important role due to their high flexibility for tailoring desired properties such as high modulus, strength and durability. Their thermal and chemical resistance is provided by high crosslinking density [170–1731.
Thermosets are the most widely used materials in reactive polymer processing. In these processes, polymer synthesis and shaping take place in a single operation. Process parameters and product quality are strongly related to the reaction kinetics of the chemical system. Thus, understanding the cure kinetics of thermosets is essential for process development and quality control.
The thermosetting materials are manufactured with resins and upon complete polymerization become infusible solids that will not soften when heated. The properties of the materials depends on their network architecture. Understanding the structure property relationships provides an important guide for useful macromolecular materials. Structural modification improves performance by imparting energy dissipative properties, thereby reducing brittleness [174].
Thermoset undergoes an irreversible chemical reaction, namely crosslinking or polymerization. It involves a time-temperature exposure during processing. The material in liquid state is formulated to cause liquid to flow into a cavity of the desired configuration. Sufficient heating induces the chemical reaction and the plastic becomes rigid. The part is then removed from the cavity. It is necessary to note the critical variable in most thermoset processing is pressure.
The polymerization of thermosets can be attained either by the initial application of heat or by the use of a chemical accelerator. Polymerization by means of heat is the general method, with the exception of the cold-setting resin adhesives generally cured by the introduction of chemical accelerator. However, in certain instances, a minimum amount of heat is essential for complete curing.
Curing is essentially the synthesis or polymerization of products which become insoluble and intractable in final form. This implies that to understand processing requires an understanding of the synthesis or curing chemistry. To characterize the final product can require analysis during curing and processing.
