Measured vinyl acetate content

Table I shows the measured vinyl acetate content of each of the samples based on the stoichiometry of every vinyl acetate group decomposing to acetic acid and a polyolefin in the initial weight loss. The DY values are those measured as the changes in weight of the sample by TGA. With the exception of the 12% nominal vinyl acetate sample, relatively close agreement was found between the nominal values and the TGA data.

Infrared spectra of packaging films with known vinyl acetate contents are recorded. The absorbance peak at 1030 cm-1 used to determine the content of the vinyl acetate was measured by the baseline method (A = log(/0//). The following results were obtained. 

There have been many studies of the most effective way to address a common feature in NIR and Raman spectra of reacting systems, viz. the change in spectral baseline. Figure 3.48(a) shows a typical output from a NIR diffuse-reflectance spectral measurement of 12 kinds of ethylene-vinyl acetate (EVA) copolymers differing in vinyl acetate content (Shimoyama et al, 1998). 

Infrared spectroscopy has been applied to the determination of free and combined vinyl acetate in vinyl chloride-vinyl acetate copolymers [19]. This method is based upon the quantitative measurement of the intensity of absorption bands in the near-infrared spectral region arising from vinyl acetate. A band at 1.63 pm due to vinyl groups enables the free vinyl acetate content of the sample to be determined. A band at 2.15 pm is characteristic for the acetate group and arises from both free and combined vinyl acetate. Thus, the free vinyl acetate content may be determined by difference at 2.15 pm. Polymerised vinyl chloride does not influence either measurement. 

It has been found that magnesium hydroxide appears to have a special synergy with polyethylene vinyl acetate [119], resulting in high levels of flame retardancy as measured by the limiting oxygen index tests (LOI) [120]. The effect of the magnesium hydroxide on the LOI of a polyethylene vinyl acetate (18% of vinyl acetate content) is presented in Table 3.3.1. 

The melt-extrusion transesterification of ethylene/vinyl alcohol (EVAL) copolymers was monitored by on-line NIR, measured at the exit of the extruder by use of a fiber-optic probe. Calibration models for predicting the vinyl acetate content in EVA copolymers were developed using PLS regression. The correlation coefficient and SEP were 0.96 and 0.85%, respectively [62]. 

The vinyl acetate content of films of ethylene-vinyl acetate copolymers can be determined by methods based on the measurement of absorbances at 16.1 and 1.39 pm [40] and at 8.03 pm and 5.73 pm [41]. The acrylate salt in acrylate salt-ethylene ionomers has been determined from the ratio absorbances at 6.41 pm (asymmetric vibration of the carboxylate ion) and 7.25 pm [42]. 

A second industrial field which has often used Raman spectroscopy and PLS analysis for quantitative modeling is in the production of polymers. PLS has been used on Raman spectra to predict the density of poly(ethylene terephthalate) [3] and polyethylene [73] and Chalmers and Everall mention crystallinity measurements for polyketones [74], Similarly, Sano and co-workers presented a density study of linear low-density polyethylene using PLS and Raman spectroscopy [75]. A subset of these authors have previously shown [45] the prediction of vinyl acetate content in ethylene-vinyl acetate copolymers. PLS was used along with PCA to study the rate constants for a synthesis and hydrolysis of ethyl acetate [29]. 

The tensile modulus for the EVA blends with 5 wt.% loading of the organomontmorillonite decreased steadily from approximately 1800 kg/cm for the EVA with 3 wt.% vinyl acetate content to approximately 250 kg/cm for the EVA that contained 26 wt.% of vinyl acetate. The addition of 10 wt. % of the PEMA with 1 % content of maleic anhydride consistently resulted in a significant increase in tensile modulus. Approximately a 500 kg/cm increase was measured for the 3% vinyl acetate containing polymer to a doubling of the tensile modulus value for the 26% vinyl acetate containing copolymer. 

Further studies carried out on an aluminum-trihydrate Ailed FRNC compound (compounding see Section 6.2) showed similar results. In Figure 10.14 the results of a torsion pendulum measurement are shown. The values of the first maximum are approximately equal to the 40,45, and 50 wt% copolymer-based compound, whereas the higher vinyl acetate content leads to increasing maxima. 

FIGURE 10.13 Glass transition temperature versus vinyl acetate content. (DSC measurements, heating rate 20°C/min.)... 

The measurements confirm the assumption derived from the chemical structure of the copolymer. Good oil resistance is found for the high vinyl acetate content copolymers, whereas those with lower vinyl acetate content show poorer oil resistance, as schematically shown in Figure 10.15. 

Many cable sheaths are mamrfactured from heavily filled polymers, and TGA has been foimd to be of immeasurable value in studies of such materials and some of their ingredients. The combination of the weight-loss curve, for quantitative analysis, with the derivative, for a qualitative interpretation, has been found to be particularly powerful for these applications particularly when taken together with data obtained by the other thermal methods already discussed but also with that obtained by FTIR spectroscopy. In addition the vinyl acetate content of ethylene-vinyl acetate (EVA) copolymer used in the preparation of some sheathing formulations has been measured and used as a confirmation of grade. 

The properties of ethylene-vinyl acetate copolymers vary widely with their ester content. At the lowest levels of vinyl acetate, they have physical properties that are similar to those of low density polyethylene. As the comonomer content increases, the material becomes less crystalline and more elastic. Copolymers made with the highest comonomer levels contain no measurable crystallinity. The resulting products are tough, flexible, and clear. The ester... 

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

CIL has influence on fire-retardant systems through viscosity as well. Nonmodified montmoril-lonite (NMM) and organophilic montmorillonite (OMM) have been introduced into ethylene vinyl-acetate (EVA) copolymer (clay content was 10%) and compared in AR 2000 type rheometer. (Measurements were performed at 210°C and 0.5% amplitude. The applied frequency range was co = 1-600 1/s.)... 

Water absorbed in a polymer can exist in an unassociated state or as a separate phase (cluster). In this investigation the DSC technique of water cluster analysis was used in conjunction with coulometric water content measurements to characterize the water sorption behavior of polysulfone and poly(vinyl acetate) The polysulfone had to be saturated above its Tg (190°C) and quenched to 23°C for cluster formation to occur while cluster formation occurred isothermally at 23°C in the poly(vinyl acetate) Both polymers showed an enchancement of their low temperature 3-loss transitions in proportion to the amount of unclustered water present. Frozen clustered water produced an additional low-temperature dielectric loss maximum in PVAc and polysulfone common to polyethylene and polycarbonate as well. Dielectric data obtained on a thin film of water between polyethylene sheets was in quantitative agreement with the clustered water data. 

Where the polymer material is a copolymer it is often possible to obtain a measurement of the relative amounts of the various monomer components from an infrared spectrum. For example, with an ethylene-vinyl acetate copolymer the relative heights of absorption bands from both the ethylene and vinyl acetate are measured and ratioed with the spectrum recorded in the absorbance mode. The most convenient absorbance bands are 720 cm for polyethylene and 1235 or 1740 cm for vinyl acetate. Copolymers of known composition are required for calibration. It is possible to obtain an assessment on the butadiene and acrylonitrile contents in styrene/ butadiene/acrylonitrile copolymers. The bands usually used are for styrene 1600 cm, for acrylonitrile 2240 cm and for butadiene 996 cm... 

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