Plastics Additives and Testing

By Muralisrinivasan Natamai Subramanian

“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.

• Language: English
• Publisher: Wiley
• Release date: Apr 18, 2013
• ISBN: 9781118710555

Book preview

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 Subramanian

Madurai

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:

1. Thermoplastics can be heat-softened and thus can be recycled. They include high- and low-density polyethylene, polypropylene, polyvinylchloride and polystyrene, etc. It has been known for many years that some of the mechanical and physical properties of thermoplastics are affected by the rate at which the sample has been cooled from the processing temperature or from some temperature at which it has been annealed or heat treated. Large effects were observed in crystalline plastics and most were easily associated with observable changes in the crystallinity or the crystalline texture. Similar changes have been seen in the mechanical properties of glassy amorphous plastics but without concomitant changes in any observable structure parameter [13].

2. Thermosets can neither be heat-soften nor are they possible to recycle. This is due to the formation of chemical crosslinks by covalent bonds. They include phenol formaldehyde, urea formaldehyde and melamine formaldehyde resins, unsaturated polyesters and epoxy resins, etc.

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]:

1. Those with carbon chain as skeleton. Examples are polyethylene (PE), polypropylene (PP), polystyrene (PS), PMMA, PVC, etc.

2. Those containing hetero atoms such as nitrogen, sulfur, oxygen, etc., in addition to carbon atoms. Examples are polyether, polyester, polyamide, etc.

3. Those with double bonds—plastics composed of higher molecular compounds. Examples are polyacetylene, polyphenylene, etc.

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