摘要:

Melt-mixed polyblends of high-density polyethylene (HDPE) and an ethylene-propylene copolymer (EPM) containing 78 mol% ethylene were studied in the complete composition range, using quenched and annealed samples. Phase contrast microscopy revealed that the polyblends are heterogeneous, the rubbery copolymer being dispersed as domains with sizes in the micron range, in the HDPE matrix. At intermediate compositions the blend structure was less uniform. DSC studies indicate that crystallization of PE proceeds independently of the rubbery component at all compositions with no evidence of cocrystallization to a significant extent. Dynamic mechanical studies, between –120° and 140°C at 110 Hz, of annealed and quenched specimens confirm that the system is incompatible; however, compound inclusions are formed at low EPM levels. At rubber-rich compositions EPM crystallinity is affected by the presence of the PE phase with the formation of a common crystalline supermolecular structure. Also, a small reduction of the crystallization temperature with an increase of EPM content and a melting point depression of PE at these compositions are evidence for the reduction of crystallite dimensions. This is further corroborated by a decrease of the α relaxation temperature.

ISSN:0022-2348    

DOI:10.1080/00222348308215195

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The properties of melt-mixed polyblends of high-density polyethylene (HDPE) and an amorphous ethylene-propylene-diene terpolymer (EPDM), containing 62 mol% of ethylene, were studied. The compositions covered the complete range. The techniques used were differential scanning calorimetry, dynamic mechanical spectroscopy, and phase contrast microscopy. The latter technique revealed a heterogeneous structure with a finer dispersion of the rubbery particles (at low rubber compositions), compared to a blend of a HDPE/ethylene-propylene copolymer (EPM) having a higher ethylene content and of low crystallinity. The dynamic mechanical technique at isochronous conditions (110 Hz), between–120° and 140°C, confirmed the heterogeneous nature of the polyblends and revealed mixed-phase formation at all rubber compositions. Appropriate mechanical models tested at -25°C revealed that the HDPE phase forms the matrix of the polyblends for volume fractions of EPDM, Φ (EPDM) < 0.8. More severe tests over an extended temperature range, using other models, led to the conclusion of a basically incompatible system of noninteracting phases with a highly parallel connectivity. This is consistent with a laminar distribution of phases. DSC studies showed that at Φ (EPDM) 8gt; 0.2, the PE crystallization mechanism changes, but there was no evidence of cocrystallization. In addition, the reorganization of the PE crystals during melting is significantly influenced by the viscous rubber surrounding it. This, together with the reduction of the α PE relaxation temperature, is taken as evidence that a limited mixing of the amorphous phases takes place within the interlamellar region, accompanied by a decrease of the crystal fold period.

ISSN:0022-2348    

DOI:10.1080/00222348308215196

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The effect of reequilibration reactions on the annealing of nylon 6 under elevated pressure has been investigated. The rate of the reactions was controlled by masking of end groups and varying the water content of the polyamide. In presence of 6% water, the initial rate of improvement of the crystals at 0.65 GPa and 284°C increases greatly, as concluded from the sharp rise in the melting temperature, the heat of fusion, and the long period. This is related to a drastic acceleration of the hydrolysis of amide groups, indicated by an almost instantaneous 10-fold decrease in the molecular weight, as revealed by viscometry. Annealing of extremely dry specimens under similar experimental conditions results in the generation of free radicals, and network formation slows down the perfection process. The present results strongly support the previous suggestion that chain scission is a predominant step in the annealing of polyamides under elevated pressure.

ISSN:0022-2348    

DOI:10.1080/00222348308215197

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The properties of PET (polyethylene terephthalate) fibers spun at high WUS (wind-up speed) have been compared with fibers drawn from low-WUS feedstock by measurements of initial modulus, birefringence, and extension to-break. Contrary to expectations, spun fibers are not like partially drawn fibers but are structurally different. Lack of appreciation of this can lead to errors when calibrations are used to characterize spun fibers which are based on the properties of drawn fibers (e.g., sonic modulus). Deformation and heat treatment of PET fibers leads to two types of crystallinity, strain induced (type I) and thermally induced (type II). Type I is due to extension of “backbone” molecules, and type II arises from epitaxial crystallization during heat treatment at constant length. In normal drawing type I is associated with extension on the hot feed roll; and type II, with the hot plate. In spinning at high WUS, type II occurs extensively at the crystallization WUS of about 4000 mpm, and thereafter type I and II occur together. When spun fibers are annealed taut there is a considerable increase in type II epitaxial crystallinity, and the difference between spun and drawn fibers can no longer be distinguished according to the criteria used.

ISSN:0022-2348    

DOI:10.1080/00222348308215198

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The addition of ethylene-propylene random copolymer (EPR) to polypropylene (PP) homopolymer and the synthesis of polypropylene/ethylene-propylene block-sequential copolymer (PP/E-P) have been developed in order to improve upon the mechanical properties of PP resin. The block-sequential polypropylene/ ethylene-propylene copolymer or the appropriate blend of EPR with PP gives improved impact properties without loss of elastic modulus [1–3].

ISSN:0022-2348    

DOI:10.1080/00222348308215199

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A method based on the melt flow index rather than the conventional zero shear viscosity is suggested to estimate the activation energy for viscous flow of polymer melts. The method is particularly attractive due to its simplicity and because all the conditions for its derivation fit rather well within the validity range of applicability of the Arrheniustype equation relating viscosity and temperature. Values of activation energy for viscous flow using the suggested technique are calculated for a number of polymers falling within the olefinic, styrenic, cellulosic, and engineering thermoplastic groups.

ISSN:0022-2348    

DOI:10.1080/00222348308215200

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The diamagnetic susceptibility χmof a series of low-density PE samples has been investigated with regard to the number of chain defects in the solid and in the liquid state. The diamagnetic susceptibility of PE rises gradually at the beginning of the melting interval, reaching a plateau which characterizes the diamagnetism of the liquid state. The percent increase in diamagnetism, δ χ, when passing from the solid to the liquid state is primarily due to an increase of intermolecular disorder of the crystalline segments and is apparently independent of the nature (conformation) of the lamellar surface. The increase of diamagnetism of liquid PE with the number of defects favors the view of a state of local molecular order in molten PE. Since the thickness of the crystalline lamellae decreases with the concentration of chain defects along the chains, the value of δ χ turns out to be a function of crystallinity of the lamellar material.

ISSN:0022-2348    

DOI:10.1080/00222348308215201

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

PVC forms gels in a number of solvents. Measurements of gel melting temperature as a function of molecular weight and concentration indicate that the cross-links result from H bonding between two segments. Crystallization in the gels in the form of two types of crystals is independent of the gel network formation, growing after the gel forms. The gel-forming ability and gel hardness are functions of the polymer-solvent interaction and the H-bonding ability of the solvent. Replicas of freeze-fracture-etched surfaces of the gels suggest aggregation of the PVC molecules in the form of a fibrous network structure.

ISSN:0022-2348    

DOI:10.1080/00222348308215202

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A number of years ago the morphology of amorphous polyethylene terephthalate (PET) quenched from the melt at 280°C into ice water and cast from solution was reported [1]. A nodular structure ca. 75 Å in diameter was described, the electron diffraction pattern consisting of a single diffuse ring. Based on brightfield and dark-field diffraction contrast micrographs, which showed the presence of ordered domains of similar size, it was proposed that the molecules in amorphous PET both above and below Tgare locally aligned and have a nematic liquid-crystal-like arrangment, in domains of the size of the nodules. The proposal of order in the amorphous material above Tgwas based on the assumption that the quenching was sufficiently rapid that the morphology observed in the glass reflected that present above Tgat the instant of quenching; in the melt itself the ordered domains were presumed to undergo continuous fluctuation.

ISSN:0022-2348    

DOI:10.1080/00222348308215203

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor