Polymer quality control

In the field of in-process analysis, analytical NMR applications also constitute a growth area - and also in relation to additives. This stems from the fact that the method makes it possible to use chemical analytical data in polymer quality control. Robust tools for hostile chemical plant environments are now available. The field of process analytical chemistry has been pushed to the forefront of the partnership between industry and academia. 

Packaging Paper, cardboard, plastics, films, adhesives Raw materials screening Physical properties, such as crystallinity - polymers Quality control... 

The complexity of molecular weight distributions (MWDs), chemical composition distributions (CCDs) and isotacticity distributions (IDs) of homo- and copolymers of propylene made with Ziegler-Natta catalysts constitutes a challenging problem for polymer quality control. These distributions affect the final mechanical and rheological properties of polypropylene (PP) and ultimately determine its applications. This issue becomes very complex with PP and copolymers of propylene and a-olefins made with heterogeneous Ziegler-Natta catalysts because polymers with broad and sometimes multimodal MWDs, CCDs and IDs can be produced. The major objective of propylene pol)onerization models is to predict these distributions and ultimately correlate them to mechanical and rheological properties [1]. 

J.W. Washall and T.P. Wampler, A Pyrolysis/FT-IR System for Polymer Quality Control - A Feasibility Study, Chemical Data Systems, Oxford, PA, USA, 1988. 

DSC is thus a quick and reliable method of analysis, not only in material development, but primarily in the areas of quality assurance, raw material control and failure analysis. DSC is used for identification of incoming plastic materials e.g. HDPE/PA6 and LDPE/EVAL/PA6 composite film. DSC can not only identify the major components of polymers, but can also detect minor components such as adhesives, if these have a melting behaviour which differs from that of the polymers. Quality control of packaging film without sample preparation is based on the measurement of the solid/liquid phase transition of melting by means of DSC. Sass [175] has given various examples of quality assurance and defect analysis of plastics by DSC. There is increased demand for sensitivity and capability because of the growing complexity of materials. 

An additional difficulty in the control of polymer properties is that in some cases the control problem is multivariable, in the sense that there are interactions between the molecular weight and composition loops and therefore when a manipulated variable is chosen to control molecular weight it may also affect composition. It is important to use process knowledge to validate the selection of manipulated variables. For example, for the polymerization reactor shown in Figure 12.33, process simulations showed that one way to decouple polymer quality control is to take advantage of the fact that polymer composition is naturally very sensitive to changes in reactor feed composition but inherent viscosity is relatively insensitive... 

Fig. 9. Batch process for cast-composite polymer-based propellants. QC = quality control.

Nuclear Magnetic Resonance (nmr). The nmr analysis has been used in the polymer industry for some time to measure properties such as amount and type of branching, polymerized ethylene oxide content, and hydroxyl content. The same techniques are applicable to waxes, and are used for both characterization and quality control. 

Energy-dispersive X-ray spectroscopy has been used for quality control and test analysis in many industries including computers, semiconductors, metals, cement, paper, and polymers. EDS has been used in medicine in the analysis of blood, tis-... 

Many researchers choose to buy expensive GPC/SEC columns from one of the major producers because that producer s columns had been used in the past or because of a successful marketing campaign by one particular producer. It should be noted that repacked columns can be obtained for a fraction of the cost of new columns. American Polymer Standards repacked columns are guaranteed to perform just as well as new columns from any company. When a column is repacked the only parts reused are the stainless-steel tube and end caps. This hardware is then repacked using new frits and new ST-DVB gel. Each column is individually tested in a quality control laboratory and shipped in the customer s choice of solvent. American Polymer Standards offers a column repacking service because it is a practical, inexpensive way for customers to acquire state of the art GPC/SEC columns. 

All processes in the production of PSS columns are controlled by an efficient multistep quality control (QC) system (25). This QC system requires complete tests and documentation for all materials used in all production stages. All QC work has to be performed by specially trained and highly skilled polymer chemists. 

The synthesis of the packing materials is done by experienced polymer chemists using standardized equipment and procedures. PSS takes special care in cleaning the sorbents after polymerization to achieve constant quality and surface chemistry characteristics. Each production step is checked separately for quality control conformity. 

Improvements in process and quality control made significant contributions to the transition from iron to steel as the major ferrous construction material over a century and a half ago. For most of that time red lead was relied upon, and not without a remarkable degree of success, as the rust-inhibitive pigment in anti-corrosive paints. In the last twenty years, however, there has been a similar dramatic change from such simple paints as red lead to synthetic polymer coatings which have as complex a technology as steel manufacture itself. 

To ensure quality control material suppliers and developers routinely measure such complex properties as molecular weight and its distribution, crystallinity and crystalline lattice geometry, and detailed fracture characteristics (Chapter 6). They use complex, specialized tests such as gel permeation chromatography (2, 3), wide- and narrow-angle X-ray diffraction, scanning electron microscopy, and high-temperature pressurized solvent reaction tests to develop new polymers and plastics applications. 

Advanced adhesives are composite liquids that can be used, for example, to join aircraft parts, thus avoiding the use of some 30,000 rivets that are heavy, are labor-intensive to install, and pose quality-control problems. Adhesives research has not involved many chemical engineers, but the generic problems include surface science, polymer rheology and thermodynamics, and molecular modeling of materials... 

When the full distribution is needed, it is measured by size-exclusion chromatography (also called gel permeation chromatography). This is a solution technique that requires dissolution of the polymer in a reasonable solvent such as tetrahydrofuran or tetrachlorlobenzene. For polymers that require exotic solvents or solution temperatures above about 150°C, a simple measurement of solution viscosity can be a useful surrogate for the actual molecular weight. The viscosity of the pure polymer (i.e., a polymer melt viscosity) can also be used. Such simplified techniques are often satisfactory for routine quality control, particularly for condensation polymers such as PET that vary in average molecular weight but usually have a polydispersity of 2. 

The effects of microsphere size distribution, drug/polymer ratio, and microsphere quality can be easily demonstrated in this laboratory model. Furthermore, as animal data and human clinical trial results are available the model becomes quite useful as a quality control method (46). 

In the Phadebas TM amylase test (72) (Pharmacia Labs) the substrate was a water insoluble cross-TTnked blue starch in tablet form which also contains some inert ingredients, sodium and potassium phosphate buffer salts and sodium chloride. This polymer was hydrolyzed by amylase into water soluble blue starch fragments. After centrifugation the absorbance of the blue supernatant was proportional to the activity of amylase present in the test samples. The day to day variation on a quality control serum had a coefficient of variation of 2.7% based on 30 days of data in our laboratory. The method is simple, reproducible and uses microquantities of serum. 

Solution viscosity measurements have sometimes been utilized as qioality control tests for this polymer. Chromatographs of three samples that showed Identical intrinsic viscosities (0.8 g/dl) in toluene are shown in Figure 9. These chromatographs indicate that the identical viscosities are the result of different combinations of high and low MW components. These three polymer samples probably have significantly different physical properties and if viscosity measurments alone are utilized for quality control purposes, they may be quite misleading. 

NMR spectroscopy is one of the most widely used analytical tools for the study of molecular structure and dynamics. Spin relaxation and diffusion have been used to characterize protein dynamics [1, 2], polymer systems[3, 4], porous media [5-8], and heterogeneous fluids such as crude oils [9-12]. There has been a growing body of work to extend NMR to other areas of applications, such as material science [13] and the petroleum industry [11, 14—16]. NMR and MRI have been used extensively for research in food science and in production quality control [17-20]. For example, NMR is used to determine moisture content and solid fat fraction [20]. Multi-component analysis techniques, such as chemometrics as used by Brown et al. [21], are often employed to distinguish the components, e.g., oil and water. 

Applications Although Soxtec combines the best qualities of reflux and Soxhlet extractions up to now fairly little evidence has been reported concerning the efficacy of this system for polymer and rubber analysis. Nevertheless, it appears that oligomers and other reaction residues, softeners, antioxidants (e.g. BHT) and several other additives used to modify polymers are easily extracted from PVC, PP, PE, PS, rubber and many other polymeric materials. Also, some leading international plastic, rubber and packaging companies have made Soxtec an integral part of their quality control routines. Some application examples where Soxtec has proved successful are [148] ... 

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