Melt Stability Research Articles

Relationship between torque and capillary rheometer thermal stability measurements for PVC compounds

AbstractA method is described to predict the time‐temperature behavior and hence thermal stability of PVC melts in a Brabender Plasticorder torque rheometer from basic rheological data(flow and thermal stability observations) obtained on an Instron capillary rheormeter. The predicted and experimentally determined values of the Brabender thermal stability are shown to be in good agreement.

Segmented polyether ester copolymers—A new generation of high performance thermoplastic elastomers

AbstractThis paper reviews a series of high‐melting thermoplastic polyether esters prepared by transesterification from dimethyl terephthalate, polytetramethylene ether glycol (MW 600–2000), and 1,4‐butanediol. The resulting copolyesters exhibit a two‐phase domain structure consisting of amorphous polyether ester soft segments and crystalline tetramethylene terephthalate hard segments. By proper selection of the relative amounts of soft and hard segments, polymers ranging from relatively soft elastomers to impact resistant elastoplastics may be obtained. The preparation, polymer structure as well as the physical and environmental properties of polyether esters are discussed. The combination of good melt flow properties, excellent melt stability, and rapid hardening rates permits the processing of these polymers by a wide variety of methods. The excellent processing characteristics in conjunction with the unusual physical and mechanical properties of segmented polyether esters has led to their wide acceptance.

The measurement of melt flow and melt stability

AbstractThe melt flow of a plastic as measured by the standard method (ASTM D‐1238) is at a high enough stress so that the flow is non‐Newtonian. If the die in the plastometer is replaced by a nonstandard, tapered die of large orifice, a lower stress can be used and the flows are shown to be comparable to Newtonian viscosities measured in a cone and plate rheometer. Under these conditions the plastometer can be used as a sensitive measure of the melt stability of a plastic.

The effect of processing on the light stability of stabilized and unstabilized polyethylene

It is shown that antioxidants previously reported to be u.v. stabilizers can be distinguished by their mode of action into two categories. These are melt stabilizers, which destroy hydroperoxides during the processing operation, and u.v. stabilizers, which have the additional ability to destroy hydroperoxides during u.v. exposure. The interdependence of the chemical changes occurring during processing and on u.v. exposure are demonstrated.

Specific circular dichroism spectra of poly-L-lysine complexes with guanosine monophosphates. The role of the 2′ OH group

The CD spectra of poly-L-lysine in the presence of 5′-GMP, 5′-dGMP, 3′-GMP and 2′-GMP have been measured at pH 7 and at low nucleotide concentrations. The binding of 5′-GMP and 3′-GMP by poly-L-lysine induces a strong negative band in the absorption region of the base and large changes at shorter wavelengths; the binding of 5′-dGMP and 2′-GMP, however, causes only minor spectral changes compared with the spectra of the components. The poly-L-lysine complexes with 5′-GMP and 3′-GMP, which differ with respect to CD spectra, temperature stability and cooperativity of melting, are described.

Polyarylsulfones, synthesis and properties,

AbstractA new class of high molecular weight polyarylsulfones is described. Polymer synthesis and structure–property relationships are discussed. The polymers are prepared by Friedel‐Crafts type polycondensation of aromatic sulfonyl chlorides with aromatic hydrocarbons. A number of Lewis acids in small quantities are useful as catalysts for the polymerization. The polymerization reaction is carried out at elevated temperatures in the melt or in solution. Inert, nonbasic solvents which are compatible with the Lewis acid catalysts such as nitrobenzene and dimethyl sulfone are useful for conducting the polymerization. Many of the polyarylsulfones are amorphous, rigid thermoplastics with unusually high softening points, having glass transition temperatures in the range of 200–350°C. Outstanding resistance to air oxidation at high temperatures is derived from incorporation of the deactivating sulfone groups in the aromatic polymer backbone. Melt stability and solubility in selected solvents are emphasized as basis for processibility by conventional solution casting and molding techniques. The combination of properties, which in addition to thermal stability includes a high level of mechanical and electrical properties, chemical inertness, and hydrolysis resistance makes these new arylsulfone polymers useful over a wide temperature range and in severe and corrosive environments.

Mechanisms of antioxidant action: Effects of sulfur compounds on the melt stability of polypropylene

AbstractThe effects of a number of sulfur compounds on the melt stability of polypropylene milled at 165°C have been studied. Dilaurylthiodipropionate (DLTP), Mercaptobenzimidazole (MBI), and Mercaptobenzthiazole (MBT) are all antioxidiants in a polymer lightly stabilized with a phenolic antioxidant although the last two are initially pro‐oxidants. 2,2′‐Dibenzoylaminodiphenyldisulfide (22BDD) is a pro‐oxidant under the Conditions studied.In the absence of a phenolic antioxidant the effectiveness of DLTP is reduced in the early stages of oxidation, with increasing concentration although its over all antioxidant activity increases. The results are consistent with the view that both radical and non‐radical processes occur concomitantly.

Abridgment of metallic arc welding electrodes a study of the effects of surface materials

To understand the effect of surface materials on metallic arc welding electrodes, something must be known as regards the fundamental theory of arc heat distribution, arc vapor resistance and similar matters which are modified by the presence of surface materials. The character of the arc may be changed by chemical and structural variations in the surface materials. Stability is one such arc characteristic. Two types of stability are recognized, — chemical and electrical. Surface materials have a significant influence on the brittleness or ductility of weld metal. They also can be used to control the arc type, four such types being recognized. The influence of surface materials on the heating of electrodes is another phase of the matter of practical significance. Surface materials may be employed to control both the operating characteristics of the electrode and the resultant weld properties. Among the operating characteristics might be mentioned stability and rate of melting. Among the weld properties are included freedom from blow-holes and tensile strength. These and other practical applications of a comprehensive knowledge of surface materials are cited in this paper.

Metallic Arc Welding Electrodes A Study of the Effects of Surface Materials

To understand the effect of surface materials on metallic arc welding electrodes, something must be known as regards the fundamental theory of arc heat distribution, arc vapor resistance, and similar matters which are modified by the presence of surface materials. The character of the arc may be changed by chemical and structural variations in the surface materials. Stability is one such arc characteristic. Two types of stability are recognized,-chemical and electrical. Surface materials have a significant influence on the brittleness or ductility of weld metal. They also can be used to control the arc type, four such types being recognized. The influence of surface materials on the heating of electrodes is another phase of the matter of practical significance. Surface materials may be employed to control both the operating characteristics of the electrode and the resultant weld properties. Among the operating characteristics might be mentioned stability and rate of melting. Among the weld properties are included freedomf rom blow-holes and tensile strength. These and other practical applications of a comprehensive knowledge of surface materials are cited in this paper.