摘要:

Three aspects of the rheological behavior of PVC are considered. These are (a) particulate flow, which occurs below the true crystal-line melting point, (b) true melting flow, which occurs at or above the melting point, and (c) the flow of PVC compounds. The effect of structural differences resulting from different polymerization temperatures employed in preparing different molecular weight polymers on the melt viscosity and flow activation energy is re-examined, and new data a r e presented to unconfound the effect of syndiotacticity and molecular weight. The three types of flow behavior of PVC are shown to be represented by three distinct flow regions. Because of thermal instability, the true melt flow region is achieved only with difficulty. However, in commercial operations this latter state is seldom, i f ever, achieved in rigid formulations. The effect of compounding additives, especially lubricants and plasticizers, and the importance of thermal and mastication history on the flow behavior are discussed with reference to the flow mechanism.

ISSN:0022-2348    

DOI:10.1080/00222347708220362

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Prof. G. Pezzin(University of Bologna, Italy). Dr. Wales will start by discussing his own results and perhaps other results on slip of PVC. Professor Lyngaae-Jorgensen will expand a little on fusion. Dr. Chauffoureaux will discuss a new topic which will be interesting for most of the technologists present who have problems with PVC processing; in particular, the problem of the measurement of friction at high temperatures. Dr. De Vries, Dr. Collins and myself can perhaps add something by answering questions.

ISSN:0022-2348    

DOI:10.1080/00222347708220363

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The viscosity and extrudate swell as functions of shear rate and temperature as well as flow profiles and complex shear modulus were measured on the melt of three suspension poly(vinyl chlorides) of different molecular weights. For all the specimens the primary particles, about 1 μ in diameter, had been previously destroyed by suitable milling. Below a distinct critical temperature the samples show a rheological behavior similar to that of slightly crosslinked amorphous polymers. Above this critical temperature the rheological properties are comparable to those of melts of amorphous polymers. The unusual rheological behavior of poly(vinyl chloride) is explained by the assumption of a network structure formed by crystallites in the melt. Because of the gradual melting of the crystallites the network becomes ineffective above temperatures of about 200°C. This temperature increases with increasing molecular weight. The assumption of crystallites acting as crosslinks in the melt is experimentally confirmed by the reversibility of the measured rheological effects, the wide melting range determined by differential scanning calorimetry, and electron micrographs which show particles of about 0.02 μm in size.

ISSN:0022-2348    

DOI:10.1080/00222347708220364

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

An investigation of the flow curves for rigid and plasticized compounds of PVC has shown that capillary rheometry on “fused” compounds is in accordance with data obtained in continuous shear. It is further concluded that the S-shaped flow curves (log shear stress against log shear rate) that can be observed are caused by the existence of stable crystallite aggregates at low temperatures and shear rates and nonisothermal conditions at high shear stresses and high shear rates.

ISSN:0022-2348    

DOI:10.1080/00222347708220365

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The behavior of polymer melts in the presence of solid walls has been studied by recording the displacement of differently colored melts of the same stock in a capillary rheometer before and after flow. For emulsion PVC (E-PVC) without lubricant and plasticizer it was found that at T = 443°K there is almost complete slip at the wall (metal). Slip of both E-PVC and suspension PVC (S-PVC) gradually decreases with increasing temperature. Since this is a reversible phenomenon it cannot be directly related to the particle structure, which disappears irreversibly with increasing temperature. For S-PVC it was further found that slip increases with increasing pressure.

ISSN:0022-2348    

DOI:10.1080/00222347708220366

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Samples of poly(vinyl chloride) plasticized with variable amounts of either dibutyl phthalate (DPB) or dicyclohexyl phthalate (DCHP) were investigated by dynamic-mechanical measurements in the β relaxation temperature range. In this range of temperature, a superposition of the relaxation due to the cyclohexyl group with the PVC β peak was found for the samples plasticized with DCHP. By studying the dependence of the activation energy and of the peak broadness on the DCHP concentration it was possible to show that the PVC β relaxation is reduced to zero at the critical plasticizer weight fraction W1= 0.2. For the PVC-DBP series the β peak disappears at the same plasticizer content. These results strengthen the hypothesis that the β peak of PVC is due to a kind of cooperative motion since 1 mole of plasticizer for every 20 repeating units of the polymer is sufficient to suppress the PVC β relaxation.

ISSN:0022-2348    

DOI:10.1080/00222347708220367

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Tensile creep tests have been carried out on poly(vinyl chloride) with small amounts of dioctyl phthalate (DOP) and dioctyl adipate (DOA) at room temperature. Creep compliance, the stress limit of approximately linear viscoelasticity, and stress dilatation are reported as functions of additive content in the time range from 10 to 1000 sec and up to 13% of additive. For both PVC-DOP and PVC-DOA, a maximum antiplasticization effect was observed at 5% additive. In the linear viscoelastic range, there were only minor differences in the degree and character of antiplasticization between the two types of blends, as visualized from dynamic mechanical data and linear viscoelastic creep compliance. The stress levels of transition from approximately linear to marked nonlinear viscoelasticity were increased during antiplasticization more than proportional to the decrease in linear viscoelastic creep compliance. This new aspect on antiplasticization showed that DOA caused stronger intermolecular interaction with the polymer compared to DOP, though less compatibility. The stress dilatation of the blends showing maximum antiplasticization was slightly lower than that of pure PVC. Nonlinear stress dilatational behavior occurred at approximately the same stress levels as the transition from linear to nonlinear viscoelasticity for both pure PVC and the blends.

ISSN:0022-2348    

DOI:10.1080/00222347708220368

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Tensile creep tests and interrupted tensile tests were performed on poly(vinyl chloride) in order to check some consequences of a rheological model previously proposed to describe the creep behavior of glassy polymers in the linear as well as the nonlinear range of viscoelasticity. The results of the interrupted tensile tests allowed us to measure the stresses borne by the elastic elements as well as the recovery stresses related to the viscous elements of the model. The level found for these stresses did not agree with the values implied by the model. We propose here an improved model consisting of a nonlinear generalized Maxwell system. It takes into account the results of the tests and explains the viscous deformation by the destruction of an initial structure present in the polymer.

ISSN:0022-2348    

DOI:10.1080/00222347708220369

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The effects of processing variables on the solid state properties of rigid PVC were studied by evaluating dynamic mechanical and tensile properties for thin film specimens of two different resins. The dynamic measurements were performed over the temperature range −1]60 to 85°C, encompassing both the low temperature β transition and above ambient a transition (Tg). Engineering tensile strengths and energies to fracture were obtained at ambient conditions for several rates of elongation. Test specimens were prepared by solvent casting and compression molding techniques and subsequently were subjected to various thermal-mechanical histories. The results obtained were similar for both types of specimens and are described below. The various thermal histories considered include: (1) quick quenching from 225°C (samples referred to as “untreated”); (2) very slow (equilibrium) cooling after annealing at Tg; (3) quick quenching from Tg. In addition, the effects of frozen stresses were examined by systematically varying the stresses imposed on samples during the cooling processes 2 and 3. Increasing the load level imposed on specimens during equilibrium cooling resulted in enhancements of the β transition loss dispersion and tensile yield strength. Changes in loading during process 3, however, had little effect on the cooled specimens. But process 3 does alter the relaxation spectrum below Tgso that additional molecular relaxation is induced between Tβand Tαas much as 45°C below the a transition. The anomalous tan δ dispersions thus produced are accompanied by diminished tensile yield strengths and greatly increased energies to fracture. The most extreme case was encountered for the “untreated” specimens which were rapidly quenched from 225°C. The loss tangent data indicate remarkable differences in the region between Tβand Tα. When comparing the dynamic mechanical data with the fracture energy results for the same samples we note that increases in the intensity of the T < Tganomalous dispersion correlate with increasing energies to fracture. On the other hand, the β transition intensity does not directly correlate. One molecular model which is consistent with these observations assumes that elongation induces a dilation of the polymer. Since most polymers possess Poisson ratios less than 0.5, the dilation will create extra internal volume (including free volume) in the polymer network. The increase in internal volume as elongation proceeds has the net effect of shifting the conditions of testing toward higher temperatures on a molecular relaxation scale permitting a higher level of molecular mobility at ambient conditions. As a sample continues to elongate one of two consequences is encountered: the imposed deformation cannot be accommodated by the available molecular mobility and the specimen fractures; or the deformation results in dilation to the extent that the response properties are shifted into a region of the relaxation spectrum where molecular mobility is sufficient for the specimen to accommodate the imposed deformation and yielding occurs. Yielding is expected if the effective temperature shifts as far as Tgbefore the sample fractures. In a case where there are additional molecular relaxation possibilities prior to the a transition, such as those in the anomalous dispersion region between Tβand Tα, sufficient dilation for yielding will be encountered before the normal Tgis reached. The anomalous T < Tgrelaxation process thus tends to promote increased elongation and higher energies to fracture in PVC.

ISSN:0022-2348    

DOI:10.1080/00222347708220370

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

This study deals with the compatibility of a poly(vinyl chloride) mixed separately with two industrial chlorinated poly(vinyl chlorides), denoted PVC/C1 and PVC/C2 (chlorine contents of 65.2 and 67.5%, respectively). The technique of mixing, examined for different compositions, is the main parameter for the compatibility of the resins. The mixtures were prepared either with a Brabender plastograph, with a milling cylinder at 190°C (the mixture being fluid), or by sintering at a temperature between 180 and 200°C under pressure. We determined the complex components of the elasticity modulus as a function of temperature (from 50 to 170°C at a frequency of 110 Hz) for each mixture, using a Rheovibron viscoelastometer. The study of the structure of the mixtures, based on the variation of the tangent of the loss modulus, allows us to say that the compatibility of polymers depends on the chlorine contents in chlorinated PVC; thus, at 65.2% the chlorinated polymer seems to be compatible with PVC, but at 67.5% the mixture shows the characteristics of a two-phase system. The compatibility is also dependent on processing methods.

ISSN:0022-2348    

DOI:10.1080/00222347708220371

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor