The appearance retention properties of poly (vinyl chloride) compounds during weathering

Damage to poly (vinyl chloride) (PVC) compounds due to thermal degradation during processing has an important influence on its subsequent weatherability. High melt temperatures and/or high residence times cause white PVC to become more yellow and colored PVC to fade and bleach more upon weathering. If high melt temperatures are used, then short residence times are needed to maintain excellent weatherability. In addition to careful consideration of extrusion conditions, stream-lined equipment is necessary to produce extrudate of uniform thermal history. Also, relatively high thermal stabilizer levels help reduce thermal damage and, therefore, improve weatherability. Impact resistance is better retained when processing occurs at higher melt temperatures. A reasonable compromise between extrusion rate and temperature must be reached to provide for adequate color and impact retention.     

The solubility of vinyl chloride in poly(vinyl chloride)

The solubility of vinyl chloride monomer (VCM) in PVC powders has been studied by equilibrium vapor pressure and microbalance gravimetric techniques at temperatures from 30 to 110°C. At temperatures and VCM concentrations above the glass transition, the solubility closely follows the Flory-Huggins equation with χ = 0.98 and is independent of temperature and of the PVC type, molecular weight, or history. In the glassy state, the VCM solubility is higher than the Flory-Huggins value and shows pronounced dependence upon time and the PVC history. These results have been interpreted through the dual-mode sorption concept of Michaels, Vieth, and Barrie: Normal dissolution follows the Flory-Huggins relation, and the additional glassy-state solubility represents the contribution of a hole-filling process. Changes in solubility with time and sample history parallel well-known volume relaxation processes, indicating that vapor solubility measurements offer a direct and sensitive measure of the free-volume state of glassy polymers.     

Dynamic mechanical analysis of poly(vinyl chloride) compounds and blends

PVC is one of the most versatile and cost effective commercial polymers. A main limitation of PVC is optimizing its fabrication characteristics and end use properties with minimum adverse effect on either. PVC compounding technology is supersensitive due to effect of subtle variations in formulations causing “inspec” products during one production run and “out-of-spec” products in another. Large variations in properties are frequently due to improper mixing. Dynamic mechanical analyses provides a method of monitoring variations in mixing and their affect on morphological structure deviations which can lead to poor processing and end use properties.     

Miscibility in poly(vinyl chloride)/chlorinated poly(vinyl chloride) blends,and blends of different chlorinated poly(vinyl chlorides)

Blends of poly(vinyl chloride) with chlorinated poly(vinyl chloride) (PVC), and blends of different chlorinated poly(vinyl chlorides) (CPVC) provide an opportunity to examine systematically the effect that small changes in chemical structure have on polymer-polymer miscibility. Phase diagrams of PVC/CPVC blends have been determined for CPVC's containing 62 to 38 percent chlorine. The characteristics of binary blends of CPVC's of different chlorine contents have also been examined using differential calorimetry (DSC) and transmission electron microscopy. Their mutual solubility has been found to be very sensitive to their differences in mole percent CCl₂ groups and degree of chlorination. In metastable binary blends of CPVC's possessing single glass transition temperatures (T_g) the rate of phase separation, as followed by DSC, was found to be relatively slow at temperatures 45 to 65° above the T_g of the blend.     

Biaxial orientation of poly(vinyl chloride) compounds: Interaction between drawing,structure, and properties

Rigid poly(vinyl chloride) (PVC) sheets were stretched uniaxially (at constant width), equally biaxially, and unequally biaxially to various draw ratios. Tensile properties, density, and birefringence of the stretched sheets were measured, and their wide angle X-ray diffraction traces recorded. Comparison of results showed the highest crystallite and overall orientation and density in the uniaxial samples, and lowest values for the equal biaxial samples. Drawing resulted in the alignment of some existing crystallites in the plane of the film, together with the formation of new mesomorphous structures. Changes in tensile strength were attributed to overall orientation.     

Modification of poly(vinyl chloride). XIX. Electroplating of poly(vinyl chloride)

As a preliminary treatment in the PVC-electroplating procedure, treatment with dimethylformamide followed by sensitization leads to a finely roughened and a highly hydrophilic surface with reducing power. This is caused by the formation of an ionic complex compound between dimethylformamide and tin(II) chloride absorbed in the PVC surface. A much more finely and deeply etched surface which exhibits higher adhesion through the mechanical interlocking effect is obtained with the PVC blends containing the plasticizer with a low value of interaction parameter and with a solubility parameter approximate to that of PVC. Adhesion of the metal layer to the PVC surface thus obtained is improved about 1.5 times by thermal aging at 120°C for 20 min.     

Relationship between gelation and wall slip in unplasticised poly(vinyl chloride) compounds

Abstract

The degree of gelation reached upon processing influences heavily the properties of poly(vinyl chloride) (PVC) made parts. Gelation involves the conversion of the initial PVC particle structure into an increasingly homogeneous melt and therefore the rheological properties of PVC at low temperatures are very different from those at higher ones. Whereas the former involves both wall slip and particle flow, the latter yields a more conventional behaviour.

As a consequence, the nature and origins of the different mechanisms giving rise to wall slip in PVC compounds must be taken into account when trying to understand the relationship(s) between the processing conditions, the physics of the gelation mechanism, and the final product characteristics.

This work involves the study of the rheological properties of PVC compounds for different initial gelation levels and the identification of wall slip mechanisms using rotational rheometry.     

Modification of pitches by poly (vinylidene chloride) and poly (vinyl chloride)

Poly(vinylidene chloride) — PVDC — and poly(vinyl chloride) — PVC — reacted with pitches at elevated temperature with an increase in the yield of residual carbon; the greater the aromaticity and ‘fixed carbon’ of the pitch, the greater the increase. PVDC especially had a remarkable effect. This increase of residual carbon may be due to an increase in the molecular weight of pitch produced by its reaction with PVDC or PVC via dehydrochlorination. This tends to elevate the softening point and increase the insolubility in solvents. It is clearly indicated from i.r. spectra that reaction takes place mainly between aromatic hydrogen in the pitch and chlorine in PVDC. X-ray diffraction profiles of the reaction products show that the pitch forms hard (non-graphitizing) carbon as the PVDC content in the mixture increases.     

Effect of compatibility between solvent and poly(vinyl chloride) on dechlorination of poly(vinyl chloride)

In this study, the use of diethylene glycol (DEG), triethylene glycol (TEG), n-C₁₀H₂₁OH, and ethylene glycol (EG) as solvents for NaOH in the dechlorination of poly(vinyl chloride) (PVC) was investigated. In the early reaction time, the degrees of dechlorination for DEG, TEG, and n-C₁₀H₂₁OH were notably higher than that for EG. Further, the high compatibility between PVC and the solvents was considered to result in the easy penetration of the solvent and OH⁻ into PVC particles, leading to the acceleration of dechlorination in the early reaction stage. An improvement of the dechlorination was actually observed for DEG and TEG compared with EG. The solvent with the best compatibility to PVC, n-C₁₀H₂₁OH, however, showed little improvement due to the formation of a protective polyene layer on the surface of the PVC particles.     

Radiation yield of hydrogen chloride in gamma-irradiated poly(vinyl chloride) stabilized by epoxy compounds

The G_HCI values of γ-irradiated PVC mixtures were studied after addition of various amounts of three epoxy stabilizers: diglycidyl ether of 2,2-bis(4-hydroxy-3-methylphenyl)propane (I); diglycidyl ether of 1,1-bis(4-hydroxyphenyl)cyclohexane (II), and butyl-cis-9,10-epoxystearate (III). The results indicated that two processes are essential for the stabilization: HCI capture by the epoxy groups, and an external protective effect, due to the remaining part of the stabilizer molecule. The role of the benzene rings in stabilizers I and II, as compared with the protective effect due to the long chains of stabilizer III, is not as dominant as one would expect.     

Degradation of poly(vinyl chloride)

The decomposition of poly(vinyl chloride) below 155°C has been examined by thermogravimetric analysis. Degradation is enhanced by irradiation with 1 MeV electrons. Later stages of isothermal weight loss for thermal and radiolytic decomposition follow 3/2-order kinetics and a similar reaction scheme is inferred. A free radical mechanism for dehydrochlorination involving allyl and polyenyl radicals is postulated.     

Chemically crosslinked poly(vinyl chloride)

The effect of mixing time, temperature, and thermal treatment on mechanical properties of crosslinked PVC is investigated. The tensile properties and gel content of crosslinked and uncrosslinked PVC molded samples are evaluated. The cured samples exhibited higher tensile strength and thermal stability than unmodified PVC.     

Wet poly(vinyl chloride) membrane

Wet, porous, and semipermeable poly(vinyl chloride) (PVC) membrane prepared from a binary system, PVC and dimethylformamide, by immersing in alcohols or ethers was studied. The pore dimensions of the wet PVC membrane were from 0.01 to 0.05 μm, calculated from hydrodynamic permeability by using experimental values such as water flux and water content. They agreed reasonably well with the dimension of the pores which prevented the protein passing through the membrane, observed by SEM photographs. Formation of the wet PVC membrane can be explained by slow phase separation and slow leaching of the casting solution immersed in alcohols and ethers such as methanol and ethylene glycol monomethyl ether.     

Dehydrochlorination of poly(vinyl chloride)

PVC has been dehydrochlorinated with alcoholic alkali in soution at 7°C for different lengths of time. At early stages of dehydrochlorination the dominant reaction is intramolecular removal of HCl and this gives rise to two intense Raman bands at ～ 1126 (ν₁) and ～ 1518 cm^?1 (ν₂) and following UV irradiation, to a quadruplet ESR spectrum. Increasing polyene sequence length and intermolecular removal of HCl at later stages of reaction alters the quadruplet signal to a singlet, shifts ν₁ and ν₂ to lower frequencies and increases the molecular weight. The presence of polyene units stiffens the chain and increases the elastic modulus. The T_g is, however, lowered slightly due to the removal of bulky chlorine atoms which relieves steric hindrance and dipole interaction between neighboring chains. The β-transition is also rendered less distinct.     

Correlation between some solution and mechanical properties of poly(vinyl chloride) and chlorinated poly(vinyl chloride)

Correlations have been found between solubility parameters and some mechanical properties of a series of vinyl polymers containing 56.6–69.9% chlorine when tested below their glass transition temperature. It is shown that stress at yield increases similarly with chlorine content and with the volume occupied by a monomer unit in the polymer. Using the Reiner-Weissenberg theory of the dynamic strength of materials as a criterion and a rheological model based on a pair of Maxwell bodies in parallel with a Hooke spring, the amount of dissipated and conserved work to yield point was calculated. A parameter, defined as the ratio of work to cohesive energy density, describes the efficiency of the system. The overall efficiency of the system, based on work to break, and proportional efficiency, based on work to yield point, are affected by chlorine content and strain rate. In addition, a potential energy parameter is defined which describes the cohesive energy per volume occupied by monomer unit of the polymer. This parameter is proportional to the total work to break as well as to the ratio of the residual work after yield to total work at all strain rates tested. The major portion of work is conserved up to yield; only a small portion is dissipated. From the yield point to break, after the onset of viscous flow, the major part of this work is dissipated.     

Reversible discoloration effects in the photoaging of poly(vinyl chloride)

It is often observed that the photochemical degradation of titanium dioxide pigmented PVC leads to a latent discoloration that is revealed only during a further period of storage of the aged material in the dark. This effect is reversible, and photobleaching can be provoked by a new irradiation of the polymer. This behavior can be attributed to the formation of polyenic sequences with a short conjugation length, which present an absorption below 400 nm. The screen effect of the pigment protects these polyenes against photooxidation, which permits these polyenes to accumulate in the degraded polymer. In the absence of light, these polyenes can be thermally isomerized, so leading to isomer forms absorbing at longer wavelength above 400 nm. This absorption is responsible for a yellowing of the polymer. The isomerization is perfectly reversible and a further irradiation provokes the conversion to the isomer form absorbing below 400 nm, leading then to a photobleaching of the sample. These experiments can be repeated many times before any distortion occurs.