Unplasticized Poly Research Articles

Smoke/Char Relationships in PVC Formulations

Two blends of acrylonitrile-butadiene-styrene with unplasticised poly (vinyl chloride) and a tertiary blend of acrylonitrile-butadiene-styrene, unplasticised poly (vinyl chloride) and poly (propylene) containing a smoke sup pressing iron compound gives good reductions in smoke and high yields of car bonaceous char when heated in air

Surface analysis and peel strength of aged, oxygen-plasma-modified unplasticized poly(vinyl chloride) films

The surface of unplasticized poly(vinyl chloride) (UPVC) was modified by oxygen plasma treatment and analysed using X-ray photoelectron spectroscopy (XPS), contact angle analysis (CAA) and 180° peel test measurements. XPS results show a surface rich in oxygen-containing species which are detectable on the surface after 10 weeks following plasma treatment. CAA results, however, indicate that an initial increase in surface energy immediately after the plasma treatment is followed by a dramatic decrease after 24 h of ageing due to a thin layer of organic contamination. Peel test results imply that oxygen plasma treatment initially increases peel strength of Scotch Magic ® tape against the surface, but after 8 weeks the peel strength decreases below that of the untreated sample, suggesting the formation of a weak boundary layer.

Plasticizer migration from plasticized into unplasticized poly(vinyl chloride)

AbstractThere exist important industrial applications, such as hoses or plastic windows, dealing with closely combining plasticized and rigid poly(vinyl chloride). Nevertheless, migration of plasticizer causes severe variation of the mechanical performance of the end‐products. This work comprises an effort to investigate and understand these phenomena, also as an extension of previous work of ours in migration to liquid environments. The common system plasticized PVC/dioctylphthalate/unplasticized PVC was studied under two‐sided diffusion conditions, i.e., from a thin sheet of plasticized sheet. The whole assembly was placed between two glass plates and then was held in an oven at 64°C to simulate accelerated test conditions. Some pressure was also applied to ensure perfect contact between the plastic sheets. Three different levels of initial plasticizer concentration (48, 66, and 100 phr) have been considered for a period of about five months, until equilibrium was reached. During this period the migration process was monitored by weight changes. Plots of Mt/M∞ vs. t½, where M∞ the amount migrated at equilibrium and Mt the amount lost at time t, resulted in evident linear relationship. Therefore, it was proved that the Fick's law approximation for short times can be used to describe the migration kinetics for this solid/solid system. On the other hand, macroscopic observations revealed that no plasticizer was accumulated at the interface, i.e. all plasticizer leaving the plasticized sheet entered the rigid ones. Finally, it seems that the controlling stage is the diffusion inside plasticized PVC while possible annealing of the plasticized polymer structure cannot be excluded.

Char formation in polymer blends

A quantitative study on the formation of carbonaceous char at 350, 500, 650 and 800°C in unplasticized poly(vinyl chloride), acrylonitrile-butadiene-styrene and especially in blends of the two polymers has been carried out. Incorporating iron compounds at varying levels into the polymer blends dramatically increases char formation even at 800°C. Flammability and smoke data are also presented and the relationship between char formation and levels of iron present are discussed. Crosslinking/char-forming schemes are proposed in an attempt to explain the action of iron compounds in these polymer formulations.

Silane cross‐linking of PVC. II. Influence of silane type and conditions on cross‐linking by water

AbstractThe cross‐linking of plasticized and unplasticized poly(vinyl chloride) (PVC) grafted with amino‐ and mercaptoalkyltrialkoxysilanes has been studied in water and in air at 20–140°C. In both media, the cross‐linking occurs faster for plasticized PVC grafted with aminosilanes; however, at temperatures above 100°C, the effect of degradation cross‐linking is apparent. For mercaptosilanes, a marked dependence of the cross‐linking rate on the silane structure was found; plasticized PVC with grafted 3‐mercaptopropyltrimethoxysilane was cross‐linked in water at 100°C after 6 h, whereas this process took 12 h for 5‐mercaptopentyltriethoxysilane. Practically no cross‐linking occurred in unplasticized PVC below Tg, whereas the rate at 100°C was comparable with that for plasticized PVC. The cross‐linking rate is affected by the chain mobility, water content, and diffusion of water into the material; a very slight dependence on the thickness of the material was found for plasticized PVC. © 1993 John Wiley & Sons, Inc.

Poly(vinyl chloride) composition. II. Study of the flammability and smoke‐evolution of unplasticized poly(vinyl chloride) and fire‐retardant additives

AbstractThe influence of natural, activated, and modified microzeolite with the general formula Me2/m · Al2O3 · nSiO2 · pH2O (where Me = Fe3+, Ca2+, Mg2+, Zn2+, K+, Na+) and an organic additive, such as ammonium sulfamate combined with ammonium sulfate on smoke formation and flammability of suspension poly(vinyl chloride) has been studied in the present work. Microzeolite in native (i.e., natural), activated, and modified forms has been found to possess both fire‐retardant and smoke‐suppressant effects in solid poly(vinyl chloride) compositions. Such effects have been best revealed by modified microzeolite containing 3,5–4% zinc. On the other hand, the ammonium sulfamate combined with ammonium sulfate is believed to act as a strong smoke‐suppressant additive. Thermogravimetric examinations and limited oxygen index measurements show that microzeolite acts as a fireresistant and smoke‐suppressant additive predominantly in the condensed phase. The ammonium sulfamate in combination with ammonium sulfate gives evidence of the same effects, mostly in the gaseous phase.

Single screw extrusion of poly(vinyl chloride): Effect on fusion and properties

AbstractThe behavior of unplasticized poly(vinyl chloride) (UPVC) during single screw extrusion was studied. The melting and gelation mechanisms under a variety of operating conditions were identified using microscopy, density measurements, and thermal analysis. The compound followed the behavior of wall‐slipping materials, the melt forming a pool near the passive flight of the screw. Gelation involved the progressive destruction of the original powder morphology and the development, upon cooling, of an entanglement network with primary and secondary crystallinity. Both the breakdown and internal fusion of the grains were observed, depending on the location of the material around the screw. Tensile yield parameters were found to be independent of the gelation level. The values of the post‐yield parameters reached a maximum for gelation levels in the range of 70% to 85%.

A simulation of the enthalpies of fusion of unplasticized poly(vinyl chloride)

AbstractEnthalpies of fusion were measured by differential scanning calorimetry for PVC compounds processed within the range 150°–220°C by twin‐screw extrusion or compression molding. It was observed that the effects of polymer molar mass (K‐value) or sample formulation on values of the experimental enthalpy change follow identical pattern as effects of the same parameter on elastic response established by rheometry. It was assumed that the “amorphous” phase is made up of a matrix of locally ordered chain segments and occluded free‐volume and that this matrix constitutes what is described as “secondary crystallinity” of bulk PVC. On the basis of this assumption, a model was developed incorporating a parameter for the contribution of enthalphy of relaxation of free volume to the observed enthalpy of fusion of the secondary crystallinity. Graphical comparison of the simulated enthalpy changes with the measured values produced accurate measures of the critical temperature where a change in melt flow activation energy has been established by rheometry. The comparison further predicts that if PVC was processed below 190°C, an increase in shear intensity should reduce the free‐volume content of the product, while processing above 200°C should result in the converse. Also, with increasing processing temperature above 200°C a shear‐independent linear decrease in free‐volume of the bulk product is suggested to be operative. Thus, the material produced by extrusion or compression molding between 190 and 200°C should be least dense and least crystalline in line with previous observations.

Factors affecting the leaching of lead from UPVC pipes

This paper summarizes the results of a series of studies on the various factors that affect the leaching of lead from unplasticized poly(vinyl chloride) (UPVC) pipes. Factors that were studied include temperature, pH and extractants. Results showed that, for a given UPVC pipe, the rate of leaching of lead depended primarily on temperature and the nature of extractants. While the rate of leaching of lead was quite low with distilled water, it was very much enhanced by the presence of low concentration of anions such as Cl(-), HPO inf4 (sup2-) HCO inf3 (sup-) , NO inf3 (sup-) , SO inf4 (sup2-) and EDTA. EDTA, being a strong complexing agent, was most effective. Rates of leaching were found to be higher at elevated temperature except in the cases of HPO inf4 (sup2-) and EDTA. Effect of pH was not pronounced. The temperature at which the UPVC pipes were extruded was found to affect the rate of leaching of lead. Pipes extruded at 190°C were found to have lower rate of leaching than those extruded at 180°C and 170°C. Analysis of the pipes by Scanning Electron Microscopy showed that the distribution of lead in the pipes extruded at 190°C was more uniform than those extruded at 170°C.

Some further studies on factors affecting the leaching of lead from unplasticized poly (vinyl chloride) pipes

Several extractants were used to further study the leaching rate of lead from unplasticized poly (vinyl chloride) pipes under different temperatures. The effects of the concentration of extractant and extraction time on the leaching of lead were also investigated. The results show that the complexing agent (EDTA) extracts much more lead from the pipes than other extractants. The study also shows that the extrusion temperature of the pipe affects the leaching rate of lead by tap water, nitrate, sulphate, carbonate, phosphate and EDTA. The lower rate of lead extraction is obtained from the pipe when extruded at 190°C as compared to those extruded at 170 to 180°C.

Weather-Induced Degradation of Plastic Pipes

Abstract A number of plastic materials, such as unplasticized poly(viny1 chloride) (uPVC), acrylonitrile-butadiene-styrene (ABS), high-density polyethylene (HDPE), poly-(vinylidene fluoride) (PVDF), and chlorinated poly(viny1 chloride) (cPVC), are available for numerous applications. uPVC and HDPE pipes are used in pressurized piping systems in Saudi Arabia for industrial, agricultural, domestic, and general-purpose applications. Some studies have been carried out to investigate the causes of failure in plastic pipes, which is very high in the area. In this chapter an overview of the failure of plastic pipes is presented, with emphasis given to failure of pipes due to severe weather conditions in Saudi Arabia.

Fracture behaviour of uPVC thin tubes at high loading rates

The use of fracture mechanics concepts in describing the failure behaviour of unplasticized poly(vinyl chloride) at high loading rates is studied. An impact test is employed which uses a gas pulse generated by a shock tube to load thin cylindrical specimens. These controlled pulses are used to internally pressurize specimens containing machined notches of different lengths or unnotched specimens. The specimen and the apparatus are both instrumented such that the pressure pulse and the resulting strain in the specimen are monitored throughout the tests to the point of fracture. Linear Elastic Fracture Mechanics (LEFM) is successfully applied to describe the fracture behaviour of the specimens at room temperature over a wide range of loading rates. A criterion is proposed by which the values ofKc andGc can independently be obtained over the range of the loading rates applied.

Temperature effects on the leaching of lead from unplasticized poly(vinyl chloride) pipes

The leaching of lead from unplasticized poly(vinyl chloride) pipes under different temperatures and by different extractants was studied. The extractants used were tap water, sodium hydrogen carbonate and disodium hydrogen phosphate solutions. The results show that for tap water and sodium hydrogen carbonate extractants, increasing the temperature generally increases the leaching rate of lead. The reverse was observed for the phosphate extractant. The study also shows that the extrusion temperature of the pipes affects the leaching rate of lead by water. Less lead is leached from pipes extruded at higher temperature.

Fatigue crack propagation in unplasticized poly(vinyl chloride): 1. Effect of mean stress

Abstract The effect of mean stress on fatigue crack growth in an unplasticized poly(vinyl chloride) (uPVC) pipe material was investigated using single-edge-notched (SEN) specimens and the results analysed in terms of fracture mechanics. Three series of experiments were conducted. In the first the fatigue crack growth rates d a d N were collected as a function of the applied stress intensity factor range ΔK (= K max − K min ) by keeping the stress ratio R(= K min K max ) constant. In the second series of experiments d a d N were obtained as a function of ΔK when the mean stress intensity factor K m was constant; and in the third series ΔK was maintained constant, d a d N were obtained with increasing K m . All experimental results were obtained and processed using computerized data acquisition systems. When the data were analysed in terms of the conventional log d a d N versus log ΔK and log K m plots the effects of R and K m on fatigue crack growth rate were insignificant. However, there was a strong dependence of d a d N on R when analysed in terms of Williams' line zone model for fatigue crack growth.

Fatigue crack propagation in unplasticized poly(vinyl chloride) (uPVC): 2. Near-threshold fatigue crack growth

Abstract A new computer-aided test method was developed to measure near-threshold fatigue crack growth rates for a 150 mm class 12 uPVC pipe. A computer program was written to drive the fatigue testing machine and an optical microscope of 0.01 mm resolution was used to determine crack growth in the single-edge-notched specimen. The efficiency and advantages of this new technique are discussed and compared to the current ASTM proposed method. For crack growth rates of the order of 10 −9 m cycle −1 the present computerized method was approximately seven times more efficient and therefore greatly minimized the testing times required to collect near-threshold fatigue data. Using this method the effects of stress ratio and level of processing on the near-threshold fatigue crack growth were investigated. It is observed that multiple crazes were predominant at stress ratios larger than 0.6 but they apparently disappeared at lower stress ratio values. This phenomenon was explained in terms of a critical stress criterion for craze formation and the elastic stress field near the crack tip. The fatigue threshold ΔK th at a crack growth rate of 5 × 10 −10 m cycle −1 was found to decrease linearly with stress ratio from 0 to 0.5 and to remain constant thereafter. The two levels of processing studied for this uPVC pipe material did not produce any effect on ΔK th .

Unnotched impact bend test assessment of the degree of gelation in unplasticized poly(vinyl chloride) pipe

AbstractIt is suggested that the unnotched impact test is suitable for quantitative quality control of unplasticized poly(vinyl chloride) pipe. The relative level of processing is assessed by the probability that failure is nucleated at a surface flaw. Tests show that this assessment is very sensitive to the level of processing.

Anomalous behavior of unplasticized PVC compounds in capillary flow

Capillary rheometry was performed over a temperature range of 170°–200°C and a shear-rate range of 3–3000 sec−1 on an unplasticized poly(vinyl chloride) compound. The data were corrected for the effect of pressure on viscosity, for pressure loss in the barrel and at the capillary entrance, and for the non-Newtonian velocity profile. The pressure coefficient of viscosity was found to be in the same order of magnitude as those previously found with linear polyethylene and butadieneacrylonitrile copolymers. The pressure–shear-rate superposition of the flow curves is valid at least approximately, although the temperature–shear-rate superposition is inapplicable. The shape of flow curves at 180°, 190°, and 200°C are concave downward when they are expressed as log-shear-stress-log-shear-rate. Similar plots at 170° and 175°C, however, are very different; shear stress is independent of shear rate at low shear rates, increases somewhat and becomes independent of shear rate again at high shear rates. There is no detectable temperature dependence of flow behavior at 170° and 175°C. Irregularly shaped extrudates were obtained at higher shear rates. At constant shear rate the irregularity increased with the length of the capillary. The effect of thermal-mechanical history on the particulate and crystalline structure is discussed with possible influence on the reproducibility of the rheological data.

Molecular orientation behaviour of uniaxially stretched poly(vinyl chloride) film: 1. Birefringence: effect of plasticizers and draw ratio above and below Tg

In order to investigate the orientation behaviour of a non-crystalline chain polymer, plasticized and unplasticized poly(vinyl chloride) films (PVC) are chosen for investigation. The following two orientation distribution functions are postulated to calculate the second moment of the molecular orientation: (a) for the unplasticized film drawn below the glass transition temperature the distribution function derived from an affine deformation mechanism is applied; (b) for the all plasticized films or for the films drawn above the glass transition temperature a compound distribution function derived from the affine deformation mechanism and that of a rubber-like chain (Langevin model) proposed by Roe et al is applied. The parameters which are included in the distribution function, viz. the ratio of the affine part to the Langevin part, the ratio of polyene to carbonyl in a heat treated film and the segment number of the Langevin chain, can be evaluated experimentally. The intrinsic birefringences of normal and heat treated unplasticized and plasticized films are estimated theoretically on the basis of additivity of band polarizabilities. The calculated birefringences and orientation distribution functions show good agreement with measured values.

Fourier Transform Infrared Study of Plasticized and Unplasticized Poly(vinyl chloride)

The molecular structure of plasticized and unplasticized poly(vinyl chloride) (PVC) has been examined. The crystalline vibrational spectrum, obtained for normal commercial PVC, is in agreement with that of extended syndiotactic PVC, prepared from urea complex. The plasticized PVC spectra indicate that the crystalline regions are not solvated by the plasticizer. The plasticizer does solvate amorphous chain segments, and this possible results in complex formation of the type C=O...Cl-C between the carbonyl of the plasticizer and the chloride atom of PVC.

A collaborative study of capillary flow of a highly lubricated unplasticized poly (vinyl chloride)

AbstractViscometric measurements carried out by ten members of the IUPAC Working Party “Structure and Properties of Commercial Polymers” is summarized and discussed. The participants in the study carried out steady flow measurements with capillary, slit, cone‐and‐plate and concentric cylinder apparatuses. Dynamic viscosities were determined with the Contraves Balance Rheometer.In this study a highly lubricated material with a relatively low molecular weight was chosen: highly lubricated to aid slip, low molecular weight to obtain a thermal transition at a relatively low temperature.The influence of capillary length and diameter on the flow curve has been the main subject of this study. Information supplementary to this was obtained with the other equipment.Above 180°C it was found that the flow curves obtained by the participants were consistent when account was taken of the lengths and radii used by the respective participant. The reason for this seemed to lie in the effect of hydrostatic pressure on the viscosity. There was no evidence at these temperatures of slip at the capillary wall. A change in the radius of the capillary did not alter the measured flow curve except at high shear rates when the effect of shear heating could be seen.Below 180°C there were indications that wall slippage or other, possibly structural, changes were taking place. However, strong evidence for this was not found by all participants and in some cases the findings were even contradictory.