Microstructure of PVC primary particles

The microstructure of suspension PVC primary particles has been revealed by scanning electron microscopy. The primary particles are composed of agglutinated domains which resemble linked sausage and in some cases are branched. Use of highly polished thin sections and special ion etching techniques appears responsible for revealing these microstructural features not previously reported by other investigators.     

Gamma radiation stabilization of PVC

A new class of additives combining heat and radiation stabilization has been shown to prevent the discoloration and associated undesirable hydrogen chloride formation encountered when PVC is exposed to sterilizing doses of gamma radiation. Various mechanisms that lead to the decomposition are described and the free radical processes that cause changes in physical and mechanical properties are discussed. The performance of the new additives demonstrates that rigid PVC can be exposed to high (> 5MRad) radiation with little or no discoloration and loss of physical properties.     

Mechanistic aspects of organotin stabilization of PVC

Prompted by commercial significance and academic interest, extensive model compound and in-situ studies of PVC degradation/stabilization appear in the literature. This paper presents the results of some in-situ studies of the chemical reaction pathways undergone by organotin thioglycollate esters during PVC stabilization. Infrared spectroscopy indicates that in the case of diocyltin bis(isooctylthioglycollate), not only is the mercaptoester/chloride generated, but also the corresponding thioglycollate (Oct₂ Sn TG). The extent to which this species is observed is dictated by the processing technique. An attempt is made to correlate the chemical reaction pathway of the organotin compounds with the changes (unsaturation) within the polymer. The possible relevance of these observations to the phenomenon of mono/di synergism is also discussed. While these studies extend our knowledge of the organotin stabilization of PVC, they also show that our understanding is far from complete.     

Study of PVC stabilization using capillary rheometry

Capillary rheometry allows monitoring of PVC thermal and shear stress degradations separately. Based on testing of PVC compounds with a capillary rheometer, stabilizers can be efficiently optimized to reduce both degradation processes. Capillary rheometry is an important tool for further improving productivity of PVC processing at high shear rates.     

Characterization of fine coal particles by steric field-flow fractionation

Steric field-flow fractionation (steric FFF) is described as a method for the separation and characterization of particulate materials of particle diameter 1 μm. The theoretical basis of steric FFF is described and the concept of apparent particle radius is introduced. Experiments are described using coal ground to a few μm mean diameter. Fractionation is demonstrated by collecting fractions and reinjecting them into the device, after which they re-emerge in a position close to that of the original fraction. A size-distribution curve is obtained and compared to those generated by other means. Possible sources of discrepancies are described. The advantages and potential applications of steric FFF to process control and coal research are discussed.     

Flexible PVC stabilization: the phosphite approach

Addressing environmental concerns while maintaining levels of performance and profitability is becoming increasingly important to processors. Advanced phosphite ester technology for flexible PVC developed by Dr. Don Stevenson, Mark Harr, Bill Hood and Tom Jennings of Dover Chemical Corporation is now demonstrating improved performance, reduced processing costs and a reduction or elimination of toxic heavy metals and solvents. Plastics Additives & Compounding reports on recent developments at Dover Chemical.     

Electrostatic and electrosteric stabilization of aqueous suspensions of barite nanoparticles

Electrostatic and electrosteric stabilization of aqueous suspensions of barite nanoparticles were investigated. The state of dispersion was evaluated in terms of zeta potential, apparent viscosity and the mean particle size of solid phase in the solution. Zeta potential, apparent viscosity and the mean particle size as a function of pH were performed in absence of dispersant. The result showed that electrostatic stabilization of the aqueous suspension of barite nanoparticles can be accomplished in low acidic and high basic range of pH. In presence of sodium polyacrylate (PAA-Na) dispersant, the isoelectric point (IEP) of the barite nanoparticles was shifted to lower pH and the negative zeta potential was increased in a large range of pH above the (IEP). The optimum amount of PAA-Na dispersant is discussed in the light of zeta potential and viscosity. It is found that the adsorption of PAA is correlated to the net surface charge of the barite nanoparticles and the fraction of dissociated polymer at pH 4, 8.5 and 10. At pH 4, the state of dispersion was achieved at higher amount of electrolyte due to the low fraction of negatively charged dissociated polymer and the positively charge particles. At basic pH, the fraction of dissociated polymer was high and the surface charge of particle was highly negative, therefore, the lowest viscosity was obtained at a small amount of PAA. In addition, the optimum amount of polymer decreased with the increase in pH of the suspension.     

New organic costabilizers for the stabilization of PVC

Organic costabilizers constitute a very important class of compounds where the replacement of heavy metals in PVC stabilizers is concerned. These materials are typically added at no more than 5% of the stabilizer formulation. They do, however, make a disproportionate contribution to performance based on addition level. This situation has spurred the search for new materials. Recent advances in this field are reviewed with particular emphasis on a new class of polyketones (pyrrolidine-2,4-diones) recently patented by Akcros Chemicals. The regulatory status, performance characteristics, and mechanism of action of this type of material are described.     

PVC密封条静电植绒胶粘剂的研制

用ＰＶＣ０密封条静电植绒胶粘剂的合成工艺及应用效果进行了论述，并以本产品与国外同类产品的使用性能进行了对比讨论，证明了该产品具有广泛的应用前景。     

Recent advances in the stabilization of flexible and semirigid PVC

Both the European and USA markets for liquid mixed metal stabilizers have moved or are moving to cadmium-free products. Self-lubricating products now dominate demanding areas such as calendering and extrusion in the European marketplace while the USA market has produced higher efficiency products by other means. In both markets, the use of organic costabilizers has played a major role in the formulation of cadmium-free products. The merits of self-lubricating technology and a new class of patented pyrrolidines are discussed here.     

A new strategy for plasticizing and stabilization of PVC mixtures

This study was undertaken to examine possible use of classic tetravalent tin‐based heat stabilizers for the preparation of a polymer plasticizer: poly(ε‐caprolactone) (PCL) and simultaneous stabilization of PVC in PVC/PCL mixtures. PCL was prepared from ε‐caprolactone (CL) by polymerization initiated by tin‐containing organic compounds and successfully used to simultaneously plasticize and stabilize PVC. Moreover, conditions under which the polymerization of CL took place directly in situ during PVC/CL mixture processing were found. The procedure yielded homogeneous plasticized PVC/PCL mixtures, which were stable and contained >90% of the original monomer content. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41066.     

True stabilization: A mechanism for the behavior of lead compounds and other primary stabilizers against PVC thermal dehydrochlorination

A free-radical mechanism by which lead compounds are thought to inhibit thermal dehydrochlorination of polyvinyl chloride (PVC) is described. This mechanism is called “true stabilization” in order to distinguish it from simple hydrogen chloride (HCl) scavenging, which is a well-known and sometimes important function of all primary stabilizers used in PVC. In true stabilization, it is thought that stearate or other aliphatic carboxylate groups (initially from lubricants) react with reservoirs of basic lead compound such as the carbonates, dibasic lead phosphite, the phthalates, or the sulfates, to give mobile carboxylates of lead. These latter salts then react with chlorine atoms released by the hot PVC, giving chlorides of lead and aliphatic carboxylate free-radicals. Hence the chlorine atoms are trapped and unable to propagate free-radical dehydrochlorination. Also it is thought that the aliphatic carboxylate free-radicals esterify PVC molecules at methylenic carbon atoms (from which hydrogen atoms have been removed by chlorine atoms giving HCl and free-radical sites in the polymer chain). Thus, unpaired electrons on the carboxylate free-radicals and on these methylenic carbon atoms in the PVC molecules are paired, so that the neighboring chlorine atoms in polymer chloromethylenic groups are stabilized. Hence loss of chlorine atoms in the free-radical dehydrochlorination of PVC is prevented. The pendant aliphatic carboxylate groups dissociate from the PVC molecules taking chloromethylenic hydrogen atoms to form acid molecules, and leaving chlorine atoms in relatively stable vinyl type groups. The aliphatic carboxylic acids react with more of the basic lead compound reservoir, giving mobile carboxylates of lead which can enter further reactions as just described. Thus, the true stabilizing mechanism is continuous and cyclic, while the reservoir of basic lead is available, and the PVC thermal dehydrochlorination will be retarded to almost negligible rates in favorable circumstances. It is thought that the behaviors of metal soaps and of organo-tin stabilizers may be encompassed within the general true stabilization concepts of free-radical exchanges and PVC esterifications described above. In these ways they also would retard PVC thermal dehydrochlorination. However, they are neutral compounds and have no basic reservoir which can react with carboxylic acids in the manner described above for lead stabilizers. Hence they are not able to confer long term stability on PVC in the way that basic lead stabilizing regimes do.     

Electrostatic charge acceptance and decay of powder coating particles

Techniques have been developed to measure the acceptance and decay of electrostatic charge on a wide variety of powder coatings. The measurement of the initial charge carried by the powder was affected by the amount of powder deposited. The decay of charge occurred within four time scales: (1) 1 sec, electron loss to air and to the metallic substrate; (2) 1 to 5 sec, electron flow to neutralize induced positive charge; (3) 5 to 100 sec, rapid decay from powder; and (4) 1,000 to 10,000 sec, very long term decay. Since the decay of charge was markedly affected by moisture and composition, the decay properties can be controlled by these parameters. A mathematical model was constructed describing the quantitative charge decay during the time period of 100 to 10,000 sec. There was considerable heterogeneity within the powders with regard to charge acceptance and interaction with moisture. These measurement techniques give information concerning electrostatic effects on particle transport, adhesion, and polymer electrostatic behavior which are very important variables in a powder coating process.     

PVC stabilization mechanisms in the light of practical results

Based on the mechanism of reaction, the function of PVC stabilizers and co-stabilizers is described. In particular, the differing light stabilization abilities of recognized heat stabilizers are demonstrated. Reasons for the differences observed are put forth with chemical explanations.     

Electrostatic dispersion of fine particles in the air

The paper studied the method of keeping fine particles from aggregating in the air by electrostatic dispersion. The effects of electrode voltage, diameter, humidity and rest time, as well as van der Waals forces, electrostatic forces and liquid bridge forces between particles on electrostatic dispersion of powder were discussed. It was shown that optimal electrostatic dispersion effect of calcium carbonate and talcum particles can be achieved with corona voltage of 29 kV, particle size of 2–25 μm, and proper rest time of 48 h. Criteria for electrostatic dispersion were put forward on the basis of experimental results. Theoretical calculation indicated that the criteria for electrostatic dispersion were in good agreement with experimental results.     

A continuous steric FFF device for the size separation of particles

A new method for the continuous separation of particles according to size is described. This method, continuous steric field-flow fractionation (cSFFF), is a modification of the recently developed steric FFF procedure. The physical basis of the method and the associated apparatus are described, and the theory of selective particle deflection is developed. Results with silica microspheres of ≈4 – 40 μm in diameter confirm the feasibility of the system, and verify the general features of the theory.