Melt index instrument

One of the most common instruments associated with the polyethylene industry is the Melt Index instrument that is found in research, product and manufacturing facilities around the globe. For commercial applications, polyethylene is sold according to Melt Index values summarized in material specification data sheets, usually by the Melt Index value determined with a 2.16 kg weight (MI ... 

The Melt Index instrument was developed by Imperial Chemical Industries (ICI) scientists [1] in the late 1930s in order to test polyethylene... 

Melt index of polyethylene may be measured on an instrument called an extrusion plastometer. (Photo courtesy of Tinius Olsen.)... 

With this much interest in polyethylene, many attempts have been made to use low frequency NMR in either the time domain or frequency domain to monitor and control the production more rapidly. Auburn International (now part of Oxford Instruments) developed a widely adopted system based on the time domain spectrometers [21]. In this case, sample preparation is no longer an issue since the system accepts either powder or pellets and no solvent is used. The Auburn systems determine crystalline and amorphous ratios, viscosity, melt index and molecular weight For other types of polymers, the list of advertised measurements include tacticity, rubber content, copolymer analysis, and various rheological properties. These values are determined by correlating several routine but laborious methods with the decay of the NMR signal under various pulse sequences. The man-hours... 

Extrusion plastometer (melt-indexer) ru A simple viscometer consisting of a heated vertical cylinder with two bores, a central one that contains a close-fitting piston and a recess for an orifice block, the other, nearby, for a thermoswitch. The orifice is 2.1 nun in diameter and 8 mm long. Plastic particles are loaded into the bore, allowed to heat for 6-8 min, then the weighted piston is released, and the extrudate is collected for a measured time internal. The melt-flow index (MFI) is stated as the rate of extrusion in grams/10 min. The instrument and its use are described in ASTM D 1238. Originally developed in 1953 for low-density polyethylene, the melt-indexer is now used with many other polymers with specific temperatures and piston weights. It... 

ASTM Method 1238, Standard Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer [6], completely defines the melt index, both the instrument and the experimental procedure. Temperatures and instrument configurations for common materials are given along with recommended calibration procedures and round-robin results. This method must be strictly followed if consistent melt index results are to be obtained. A melt index measurement is performed at low stress levels compared to capillary rheometers measurements (typical weights are in the range of 1.2-21.6 kg) and is sensitive to variations in operating procedure, instrument cleanliness (between tests), and operator bias (items such as packing and sample preparation). 

Traditional methods of additive analysis and the required instruments are often expensive and require the efforts of a skilled technician or chemist. In some cases a single instmment can not provide analyses for the wide variety of additives a particular organisation utilises. Additionally, laboratory techniques rarely provide results in a timely fashion. Determination of physical properties is not the least important if one thinks of pigments, talc and other fillers. Application of spectroscopic techniques to polymer production processes permits real-time measurement of those qualitative variables that form the polymer manufacturing specification, i.e. both chemical properties (composition, additive concentration) and physical properties (such as melt index, density). On-line analysis may intercept plant problems such as computer error, mechanical problems and human error with respect to additive incorporation in the resin production. Characterisation and quantitative determination of additives in technical polymers is an important but difficult issue in process and quality control. 

The most common capillary instrument in the polymer industry is not a rheometer but an indexer. The quality of nearly every batch of thermoplastic made in the world is controlled by melt index. Because it is so widely used and has all the essential features of a capillary rheometer, and because rheologists ate often asked to compare their results to melt index values, we need to examine it here. 

Such an instrument could measure true viscosity, but one would need to use other dies and weights. With such a short die entrance, losses can consume up to half of ptot (recall Figure 6.2.9). Also the ratio of die to reservoir radius is rather large, R/Rr = 0.219, so reservoir losses are significant. Thus the melt index number is a combined measure of shear and extensional viscosity. 

Some of the simplest techniques and instruments are valuable tools for chemical analysis. This chapter is designed to remind students that simple, rapid methods are advantageous in many situations. These methods are often used for quality control purposes. The methods discussed here are melting and boiling points, viscosity, density or specific gravity and refractive index. 

Instrumental methods in chemistry have dramatically increased the availability of measurable properties. Any molecule can be characterized by many different kinds of data. Examples are provided by Physical measures, e.g. melting point, boiling point, dipole moment, refractive index structural data, e.g. bond lengths, bond angles, van der Waals radii thermodynamic data, e.g. heat of formation, heat of vaporization, ioniziation energy, standard entropy chemical properties, e.g. pK, lipophilicity (log P), proton affinity, relative rate measurements chromatographic data, e.g. retention in HPLC, GLC, TLC spectroscopic data, e.g. UV, IR, NMR, ESCA. 

Solderable wires are used in telecommunications and the construction of analytical instruments, but they are becoming more and more common in small motors and dry-type transformers. The special characteristic of solderable wire enamels is the direct soldering. When the enameled wire is dipped in a solder bath at temperatures above 350 °C the coating melts and leaves the bare copper wire, avoiding the need for elaborate mechanical or chemical removal of the enamel. This characteristic achieved in solderable poly(ester-imide) by a special polymer composition and in polyurethane based wire enamels is due to the thermally reversible splitting of the polyurethane group. Nevertheless, good thermal stability is necessary and product temperature indexes >155 are required. For temperature indexes of 130, simply polyurethane wire enamels were used. 

Nevertheless, the melt flow indexer is a very useful instrument besides measuring MFI. It can be used for studying plastic thermal degradation, by consecutive running of the same material or by running hot melt slow and recording MFI over time. By doing so, various antioxidants and their various amounts can be tested... 

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