Glossary

Plastics Glossary - M

Machine shot capacity Generally based on polystyrene. This is the maximum weight of plastic that can be displaced or injected by a single stroke.

Machining Any of a number of processes, such as drilling, turning, sanding, etc., which may be performed on a piece of plastic.

MacMichael Viscometer Viscometer that consists of an outer cylinder rotated by a variable-speed motor; the measured torque exerted on an inner cylinder is a function of the viscosity of the test fluid. It is suitable for non-Newtonian suspensions.

Macromolecule Very large molecule, generally of polymer.

Manifold block Steel block on the machine that houses hydraulic valves.

Manifold Configuration of piping in a block of metal that takes a single channel flow and divides it into various flow channels to feed more than one area as in hot manifold polymers or water manifold in-mold cooling.

Mar Resistance The resistance of glossy plastic surfaces to abrasive action.

Master Batch Blend of several minor ingredients that is used later in the compounding of a product.

Master Viscometer Glass viscometer (capillary) with a liquid driving head of 400 mm or better, designed to minimize errors due to surface tension, kinetic energy, and capillary end effects.

Masterbatch A concentration of pigment, additives, filler, etc. in a base polymer. The mixture is added in small amounts to a large volume of material (the same as or compatible to the base polymer) to produce the desired mix. See LDR.

Material Safety Data Sheets Documentation regarding the toxicity or hazards associated with contact with some substances. These are prepared by the manufacturer of the plastic.

Maximization Concerted effort to increase the efficiency of a process through the most appropriate combination of instruments and techniques.

Maxwellian Fluid Viscous fluid in which the stress-strain relationship includes the relaxation effect (time of relaxation of elastic stresses set up by sudden deformation).

Mayonnaise Technique Emulsification procedure in which the ingredients are added alternately.

Mechanical Property Properties of plastics which are classified as mechanical include abrasion resistance, creep, ductility, friction resistance, elasticity hardness, impact resistance, stiffness and strength.

Meld lines The marks visible on a finished part made by two flow fronts, traveling parallel to each other, meeting during molding. Areas in the part where two different fronts of molten plastic have come together at a "meeting" angle greater than 135°F.

Melt air shot A sample of the melt when taken on cycle under representative molding conditions which will indicate the actual temperature of the melt.

Melt decompression A machine control function where the screw is pulled back inside the barrel to suck the plastic back up inside the nozzle.

Melt fracture An irregularity in the extrudate. Melt fracture may be a slight ripple or a large annular distortion in the entire cross section. Possibly caused by non-uniform or irregular strain in material at die entrance, or sticking and slippage of materials. Can sometimes be observed at the nozzle exit during purging.

Melt front The leading edge of the flow of plastic in the mold.

Melt index The amount of extruded molten plastic through a die of a specific length and diameter. The conditions of the test (e.g., temperature and load) should be given. Frequently, however, the manufacturers’ data list only the value, not the condition as well. (Note: This test is performed at a very low shear rate; grams per 10 minutes, while typical injection molding is at grams per fraction of a second!)

Melt instability An instability in the melt flow through a mold or die that causes irregularities in the finished part.

Melt Plastic that is in a molten state or above the melting point. Melt air shot A sample of the melt when taken on cycle under representative molding conditions that will indicate the actual temperature of the melt.

Melt Strength The strength of the plastic while in the molten state. This is a pertinent factor in extrusion, blow molding and drawing of molten resin from a die.

Melt temperature The temperature of the plastic as it exits the molding machine nozzle. The preferred method for measuring melt temperature: Use a calibrated, hand-held pyrometer. Preheat the probe to 30ºF above the front zone set point then place the probe in the middle of a purge patty that was taken on-cycle. Approximately 30 seconds later, the reading will stabilize at the melt temperature.

Melting point (TM) The temperature at which the crystalline regions break apart and begin to flow. See crystalline melting temperature.

Memory The tendency of a plastic article to revert in dimension to a size previously existing at some stage in its manufacture.

Mer The repeating structural unit of any high polymer. Derived from Greek, Meros.

Metalizing Applying a thin coating of metal to a nonmetallic surface. May be accomplished by chemical deposition or by exposing the surface to vaporized metal in a vacuum chamber.

Metering screw An extrusion or injection screw that has a shallow constant depth and pitch section over a series of flights at the output end.

Metering section of screw Shallow end of screw that is used in the final plasticizing of the melt in injection molding.

Metering section The front end of the screw where the fight depth is constant.

Micelle Small aggregation of surfactant molecules in a suspension. If water is the dispersing medium, the molecules are orientated with the hydrophilic end toward the water phase and the lipophilic ends together.

Micron Unit of length, equals 1 micrometer or 0.001 mm.

Microprocessor The basic element of a central processing unit developed on a single integrated circuit chip. A single integrated chip provides the basic core of a central processing unit, even though it may require additional components to operate as a central processing unit.

Migration The extraction of an ingredient from a material by another material; such as the migration of a plasticizer from one material into an adjacent material with a lower plasticizer contact.

Milling Final "polishing" operation (prior to packaging) to improve the stability of a grease by modifying its gel structure.

Mineral Reinforcements Inorganic substances used as filler for plastics. Some common examples are: clay, mica, talc.

Minimum Specifications The minimum values, usually of mechanical properties, that a compound must meet by Quality Assurance prior to shipment.

Miscella Solvent-oil solution obtained in the extraction of certain oil seed and containing mucilaginous materials that may be difficult to separate.

Mixture Material composed of two or more substances, each of which retains its own characteristic properties.

Modified Resins Synthetic resins modified by the incorporation of natural resins, elastomers or other additives, which alter the processing characteristics or physical properties of the basic resins.

Modifier Additive that changes the nature of a product or the process by which it is produced.

Modulus in Compression The ratio of compressive stress to strain within elastic limits of the material.

Modulus in Flexure The ratio of the flexure stress to strain, within elastic limits of the material.

Modulus in Shear The ratio of shear stress to strain within elastic limits of the material.

Modulus of Elasticity The ratio of stress to corresponding strain below the proportional limit of a material in tensile testing.

Modulus of Resilience The energy that can be absorbed per unit volume without creating a permanent distortion.

Modulus Stiffness a material’s resistance to deformation under load.

Modulus Derived from the Latin world meaning "small measure", modulus is the ratio of stress to strain in the linear region of the s-e curve.

Moisture Absorption The pick-up of moisture from the environment by a material.

Moisture marks or welds Marks on the finished part that are caused by moisture in the resin and look like weld lines. However, they may not be in the areas in which weld lines are expected.

Moisture vapor transmission The speed of permeation of water through a material of a specific temperature and relative humidity rate.

Molar Volume Molecular weight of a substance divided by its density.

Mold (v) To impart shape to a plastic mass by means of a confining cavity or matrix.

Mold A hollow form or cavity into which molten plastic is forced to give the shape of the required component. The term generally refers to the whole assembly of parts that make up the section of the molding equipment in which the parts are formed. Also called a tool or die. Also, molding: action of forming the part; the operation required for forming parts.

Mold base An assembly of precision steel plates that holds or retains the cavities or cores in a mold. Provides a means for melt to be injected into the cavities and provides a means to eject the solidified parts from the mold. The part of the mold that holds the cavity, core and pins.

Mold closed timer The timer that is used on some machines to control the total amount of time that the mold is closed, thus controlling all of the cooling time.

Mold height Overall thickness of the mold as it is located between the platens of the molding machine.

Mold open timer The tier that is only used in the fully automatic mode to control the total time the mold is open.

Mold protection switch One of the names of the clamp limit switch that activates the clamp into high pressure during closing just before the mold faces touch.

Mold release agent Provides an interfacial layer between two surfaces to prevent adhesion of one to the other.

Mold Release In injection molding, a lubricant used to coat the surface of the mold to enhance ejection of the molded article or prevent it from sticking to the tool.

Mold shrinkage See Shrinkage.

Mold, Blow Tool used to form hollow plastic products, such as bottles and cans. Generally made of aluminum, molds can have either water jackets, cast in tubing, or drilled cooling lines. Isolated areas, such as threads or pinch edges, can be inserted in steel for longevity. Molds are equipped with a method for injecting air into the cavities.

Mold, Injection Tools used to form a product using the injection molding process. Types include hand, two-plate, three-plate, insulated runner, hot-runner, and structural foam molds. Materials commonly used are tempered aluminum, steel, prehardened steel, hardened tool steel,stainless steel, beryllium copper, and kirksite.

Mold, Rotational Molds are manufactured from electro-formed nickel, vapor deposited nickel, and cast aluminum. The thickness of the parts is controlled by heat sinks fabricated into the tool. The tool must be temperature controlled so it will cure the resin within it.

Mold, Thermoforming Tools that form pre-extruded sheets by means of temperature and vacuum and/or pressure. Generally made from aluminum, either cast or machined.

Mold A hollow form or cavity into which molten plastic is forced to give the shape of the required component. The term generally refers to the whole assembly of parts which go to makeup the section of the molding equipment in which the parts are formed. Also called a tool or die. Also, molding. (v) Action of forming the part; the operation required for forming parts.

Molded-in stress Orientation stress within molecules and compressive and tensile stress between molecules as a result of the molding process.

Molding cycle The period of time required to complete the molding of a part. In injection molding, the cycle begins when the mold closes and ends with the opening of the mold and ejection of the molded part. The events that make up a complete operating sequence of the machine to mold a part.

Molding Pressure The pressure applied to the ram of an injection machine or press to force the softened plastic completely to fill the mold cavities.

Mole Mass numerically equal to the sum of the atomic weights of all the atoms in a molecule.

Molecular Association Aggregation of single molecules into complexes containing two or more molecules.

Molecular weight (MW) The sum of the atomic weights of all atoms in a molecule.

Molecular weight distribution The relative amounts of polymers of different molecular weights (MW) that make up a specific polymer.

Molecule The smallest unit of a substance which can exist by itself and retain all of the properties of the original substance. Molecules are composed of one or more atoms.

Monomer A relatively simple compound, usually containing carbon and of low molecular weight, which can react to form a polymer by combination with itself or with other similar molecules or compounds.

Morphology Refers to the structure of the polymer material.

Moveable mold half The half of the mold that is attached to the moving platen, sometimes called the core half of the mold. This half of the mold contains the ejection system.

Multiple Emulsion Emulsion in which the disperse phase contains globules of the continuous phase.

Multiple stage screw Extruder and injection molding machine screws which contain changes to the flight helix to perform special functions, such as feeding, mixing, and metering.

Multiple-phase blend A type of polymer modification in which the parent homopolymers are not miscible in each other and each maintains a distinct phase (distinct area) in melt and solid states. This is a physical combination.