Plastics can present a very difficult challenge to the analyst. The plastic may contain a variety of additives, including other polymers, which are used to enhance the properties of the plastic compound. For example, plasticisers, inorganic fillers, antidegradants, fire retardants, and specialist additives such as antistatic agents and cross-linkers. It is unlikely that more than 90-95% of a complex formulation can be determined by analysis alone. Compounds may contain over 10 different ingredients, some present at very low levels. It is evident that a good plastics analyst must have a working knowledge of plastics technology to succeed.
Plastics analysis is used for a variety of purposes such as quality control, reverse engineering (deformulation) and to determine causes of failure.
A wide variety of techniques can be used to discover different facts about a plastic compound. For example, elemental analysis may be required, or an instrumental method to determine the material's resistance to oxidation.
Many spectroscopic techniques are employed in plastics analysis including infrared spectroscopy, ultraviolet light spectroscopy, NMR spectroscopy, atomic absorption spectroscopy, X-ray fluorescence spectroscopy, raman spectroscopy and energy dispersive analysis. Chromatographic methods include gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), gel permeation chromatography (GPC) and thin layer chromatography (TLC). Thermal techniques include differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA).
This review outlines each technique used in plastics analysis and then illustrates which methods are applied to obtain a particular result or piece of compositional information. For example, polymer and filler identification, molecular weight determination, antidegradant quantification and surface analysis study methods are all included.
The review also includes useful sections on specific areas, such as tests for plastics in contact with food, analysis of plastic laminates and fibres, and stabilisers in PVC
This text is a good introduction to a very complex subject area and will enable the reader to understand the basic concepts of plastics analysis.
Around 400 abstracts from the Polymer Library database accompany this review, to facilitate further reading. These include core original references together with abstracts from some of the latest papers on plastics analysis. These give examples of applications of the different techniques and some new developments.
2 Analytical Techniques
2.1 Wet Chemistry Techniques
2.2 Spectroscopic Techniques
2.2.1 Infrared Spectroscopy (IR)
2.2.2 Ultraviolet Light Spectroscopy (UV)
2.2.3 Nuclear Magnetic Resonance Spectroscopy (NMR)
2.2.4 Atomic Absorption Spectroscopy (AAS)
2.2.5 X-Ray Fluorescence Spectroscopy (XRF)
2.2.6 Raman Spectroscopy
2.3 Chromatographic Techniques
2.3.1 Gas Chromatography-Mass Spectrometry (GC-MS)
2.3.2 Gas Chromatography (GC)
2.3.3 High Performance Liquid Chromatography (HPLC)
2.3.4 Liquid Chromatography-Mass Spectroscopy (LC-MS)
2.3.5 Gel Permeation Chromatography (GPC)
2.3.6 Thin Layer Chromatography (TLC)
2.4 Thermal Techniques
2.4.1 Differential Scanning Calorimetry (DSC)
2.4.2 Dynamic Mechnanical Thermal Analysis (DMTA)
2.4.3 Thermogravimetric Analysis (TGA)
2.5 Elemental Techniques
2.6 Microscopy Techniques
2.7 Miscellaneous Techniques
3 Determination of Molecular Weight and Microstructure of Plastic Polymers
3.1 Determination of Molecular Weight
3.1.1 Gel Permeation Chromatography (GPC)
3.1.4 Light Scattering
3.1.5 Other Methods
3.2 Monomer Types and Microstructure
4 Determination of Polymer Type
5 Determination of the Plasticiser and Filler in a Plastic Compound
5.1 Determination of Plasticiser
5.2 Determination of Fillers
5.2.1 Particulate Fillers
5.2.2 Fibrous Fillers
6 Determination of Stabilisers in a Plastics Compound
6.1 UV Stabilisers
7 Determination of Functional Additives
7.1 Process Aids and Lubricants
7.2 Slip Additives
7.4 Antistatic Agents
7.5 Crosslinking Agents and Co-Agents
7.6 Blowing Agents
7.7 Flame Retardants
7.8 Impact Modifiers
8 Analysis of Plastics for Food Contact Use
8.1 Global Migration Tests
8.2 Specific Migration and Residual Monomer Tests
9 Determination of Stabilisers in PVC
10 Analysis of Plastic Laminates and Fibres
11 Surface Analysis of Plastics
11.1 X-Ray Photoelectron Spectroscopy (XPS)
11.2 Laser Induced Mass Analysis (LIMA)
11.3 Secondary Ion Mass Spectroscopy (SIMS)
12 Failure Diagnosis
12.1 Common Compositional Problems
12.2 Environmental Stress Cracking
12.3 Contamination Problems
12.4 Odour and Emissions Problems
Appendix 1 Solubility Parameters of Plastics, Plasticisers and Typical Solvents
Appendix 2 Specific Gravities of Plastics and Compound Ingredients
Abbreviations and Acronyms
Dr Martin Forrest has worked in the Analysis Section at Rapra for over fourteen years. He is currently Principal Consultant Analyst, a position he has held for the past four years. He has experience in the analysis of a wide variety of polymers and polymer products using a range of techniques. He is one of the principal contacts at Rapra for projects involving plastics analysis.
Rapra has been serving the polymer community for over 80 years and was formerly known as the Rubber and Plastics Research Association of Great Britain. Rapra provides comprehensive analytical services to industry, research organisations and individuals using spectroscopic (FT-IR, infrared microspectroscopy, UV/vis spectroscopy),chromatographic (LC-MS, HPLC, GPC including triple detection, GC, GC-MS), thermal (DSC, TGA, DMTA, thermal diffusivity) and a range of wet chemical and other general and specialist techniques.