Stability PVAC

Paxnol ALES Paxnol LES Paxnol PLES foam builder/stabilizer, PVAc acrylic emulsions... 

In poly(vinyl acetate) copolymer emulsions, the properties are significantly affected by the composition of the aqueous phase and by the stabilizers and buffers used iu the preparation of these materials, along with the process conditions (eg, monomer concentrations, pH, agitation, and temperature). The emulsions are milk-white Hquids containing ca 55 wt % PVAc, the balance being water and small quantities of wetting agents or protective coUoids. 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

Other components in PVAc-formulations are defoamers, stabilizers, filler dispersants, preservatives, thickeners (hydroxyethylcellulose, carboxymethylcellu-lose), polyvinyl alcohols, starch, wetting agents, tackifiers, solvents (alcoholes, ketone, esters), flame retardants and others. 

Direct insertion probe pyrolysis mass spectrometry (DPMS) utilises a device for introducing a single sample of a solid or liquid, usually contained in a quartz or other non-reactive sample holder, into a mass spectrometer ion source. A direct insertion probe consists of a shaft having a sample holder at one end [70] the probe is inserted through a vacuum lock to place the sample holder near to the ion source of the mass spectrometer. The sample is vaporized by heat from the ion source or by heat from a separate heater that surrounds the sample holder. Sample molecules are evaporated into the ion source where they are then ionized as gas-phase molecules. In a recent study, Uyar et al. [74] used such a device for studying the thermal stability of coalesced polymers of polycarbonate, PMMA and polylvinyl acetate) (PVAc) [75] and their binary and ternary blends [74] obtained from their preparation as inclusion compounds in cyclodextrins. 

The first synthetic polymers to be used as paint varnishes were acrylic and vinylic resins. Poly(vinyl acetate) (PVAc), commercialized under the name Mowilith by Hoechst and Vinylite by Union Carbide, has been used in conservation as an adhesive since 1932 and in 1937 it was proposed as a picture varnish by Stout and Cross [63]. PVAc was soon rejected as a varnish because, despite its light stability and good solubility in organic solvents, it demonstrated poor optical properties in terms of colour saturation and the tendency to pick up dirt due to its low glass transition temperature. 

It was observed that both the poly (vinyl acetate)(PVAc) and poly(methyl methacrylate) (PMMA) latexes stabilized by PIB and... 

When pressure is applied to the latex, the UCFT is seen to move to higher temperatures as indicated in Figure 2. It was found that the PMMA latex stabilized by PIB of Mn - 2 x lCrcould be fitted to the same curve as the PVAc latex stabilized by PIB of Mjj 4 x 10. A linear regression analysis of the UCFT as a function of applied pressure gave ... 

Another attractive quality of the PVA is its outstanding chemical stability. Peter and Stefan ( ) investigated the chemical stability of PVA vis a vis a series of solvents and reagents and some of their results are summarized in Table I. This table presents a comparison between the chemical resistances of PVA, polyvinyl butyral(PVB), polyvinyl acetate(PVAc), and cellulose acetate(CA). It is evident from this table that the PVA is considerably more stable than the rest of the tested materials. 

Grafting and Stabilizers. The degree of grafting of poly(vinyl acetate) (PVAc.) on poly(vinyl alcohol) (PVA) and other stabilizers during emulsion polymerization strongly affects latex properties such as viscosity, rheology, and polymer solubility. 

Another important application is the introduction of a thermoplastic such as poly(vinyl acetate), PVAc, into an unsaturated polyester resin to improve dimensional stability of the mold part. Keeping in mind (sec. 2.3.2) that an unsaturated polyester is dissolved in styrene, the modifier is the third component and the behavior is described with the help of a ternary-phase diagram (Fig. 8.3, Suspene et al., 1991). 

Fig. 19 n-< A > isotherms for 72 mol % PVP/PVAc mixed monolayers on water at 25 °C by stepwise addition and compression. Surface pressure 77 for 72 mol % polyfvinyl palmitate)/poly(vinyl acetate) binary mixture as a function of area per monomer. The surface concentration was controlled as noted in the plot. For the stepwise-addition technique, lens formation was observed in the region where the two techniques differ for 77 lOmNm-1. For the plot, the mixture required stabilization times considerably longer than the 1-2 hours allowed between points to form equilibrium films. < A > = average area per monomer... 

Aizpurua et al. [96] have studied the kinetics of vinyl acetate miniemulsions stabilized with PS or PVAc. Guyot and coworkers [97] used PS as the costabilizer for the mini emulsion encapsulation of pigment. Samer [67] has used PMMA to stabilize MMA miniemulsions for continuous polymerization in a CSTR. 

PVAc is also the precursor to a few other types of adhesives. For example, poly (vinyl alcohol) (PVA), -[CH2-CH(OH) , is formed by the hydrolysis of PVAc. Low molecular weight grades of PVA are used in PVAc emulsions to improve colloidal stability of the emulsions, i.e., as a protective colloid. Higher molecular weight grades, only partially hydrolyzed, modify other properties such as adhesion, viscosity, and film formation. 

Kollicoat SR 30 D is a sustained release coating dispersion marketed by BASF based on PVAc. Kollicoat SR 30 D is a 30% (w/w) dispersion of PVAc (27%) in water stabilized by povidone (2.7%) and sodium lauryl sulfate (0.3%) prepared by an emulsification... 

Oxygen Quenching in Poly(vinyl acetate) Particles. In order to study a system in which fluorescent groups could be Introduced into both the stabilizer and core polymers, we turned our attention to poly(vinyl acetate) [PVAc] particles sterically stabilized by poly(2-ethylhexyl methacrylate) [PEHMA] (14,15). Phenanthrene [Phe] was chosen as the fluorescence sensor. It was Introduced into the stabilizer by mixing a small amount (ca. 1%) of 9-phenanthrylmethyl methacrylate 1. with EHMA in the synthesis of PEHMA. It was introduced into the core polymer by mixing a trace (ca. 0.01%) of J with VAc in the presence of unlabelled PEHMA in the particle synthesis step. 

Advastab . [Mmton Int L Morton bit l. NV SA] Organotin compd. lubricating stabilizer for PVC pipe, rigid sheet-mg, moldings, extrusions, bt es, o-files, PVC-PVAc systems catalyst for rigid and flexible systems. 

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