Ten different polymers were selected as possible matrix for zeolite containing desiccant composites in order to prepare functional packaging material. Water uptake was determined at 100 % RH and the results were analyzed to identify factors influencing the capacity and rate of water adsorption. The results showed that the desiccant can adsorb considerable water in its free pores. The adsorption capacity of the composites depends linearly on the amount of desiccant present, but it is independent of the type of polymer used.The diffusion of water into the composites is fast initially, but slows down with time and also with increasing desiccant content. This latter effect can be explained with the increase of the diffusion path as zeolite content increases. The initial rate of diffusion depends solely on the specific free volume of the matrix and this factor influences strongly also the overall rate of water adsorption. However, this latter characteristic depends also on other factors like the dispersion of the desiccant in the matrix. Matrix type and zeolite content must be selected according to the task to be fulfilled; fast adsorption can be achieved only with polymers having large free volume.
A large number of high‐density polyethylene (HDPE) powder samples produced by Phillips technology were taken from an industrial polymerization reactor and their catalyst residue content was determined by X‐ray fluorescence spectroscopy. The chemical structure of the powder was characterized by diffuse reflectance infrared spectroscopy (DRIFT), while the functional group content of samples processed in the presence and absence of a phenolic antioxidant was determined by Fourier transform infrared spectroscopy (FTIR). The melt flow index (MFI) of all processed samples was measured. Oxygen induction time (OIT) measurements were carried out to characterize the oxidative stability of 15 selected stabilized samples. The results indicate that the distribution of both the amount of chromium‐based catalyst residues and their composition are very heterogeneous in the produced polymer. With increasing catalyst residue content, the concentration of double bonds increases in the samples extruded with or without stabilizer. Viscosity was not influenced by catalyst residues, while discoloration increased slightly with increasing catalyst residue content. The stability of the processed polymer also depends on the concentration of double bonds and on other factors. Since other components of the catalyst, including the SiO2 support, also take part in the reactions occurring during processing, chromium content is not the sole, and perhaps not even the decisive, factor determining the properties and especially the stability of HDPE produced by a Phillips catalyst.
The number of functional and smart packaging materials increases continuously and they are used already in everyday practice in increasing quantities [1][2][3][4]. The main functions targeted for various products are small oxygen permeability or oxygen scavenging [5][6][7], humidity control [8][9][10][11][12], regulated ethylene content [13], antimicrobial effect [14][15][16][17], adsorption of odorous materials, or the opposite, the release of desirable aromas [18,19]. Intensive research and development work is carried out on these materials all over the world, but mostly in industry.Controlling oxygen permeability is especially important in the pharmaceutical industry and in food packaging. The oxygen permeability of polymers varies in a wide range covering several orders of magnitudes from a few hundred to a few hundredths or even thousands of cm 3· mm/m 2 /24 h/bar [20]. Ethylene-vinyl alcohol copolymers (EVOH) offer extremely good protection against oxygen [20][21][22][23][24][25]. The barrier properties of these materials depend on ethylene content [23,26,27], crystallinity, temperature [22,28] and humidity [24,[26][27][28][29][30][31][32][33][34]. The last factor represents also the major drawback of EVOH, since permeability may increase by orders of magnitudes with increasing water content [28] Abstract. Poly(ethylene-co-vinyl alcohol) of 48 mol% ethylene content was modified with N,N!-bis(2,2,6,6-tetramethyl-4-piperidyl)-isophthalamide (Nylostab SEED) to decrease the oxygen permeability of the polymer. The additive was added in a wide concentration range from 0 to 10 wt%. The structure and properties of the polymer were characterized with various methods including differential scanning calorimetry, X-ray diffraction, mechanical testing, optical measurements and oxygen permeation. Interactions were estimated by molecular modeling and infrared spectroscopy. The results showed that oxygen permeation decreased considerably when the additive was added at less than 2.0 wt% concentration. The decrease resulted from the interaction of the hydroxyl groups of the polymer and the amide groups of the additive. The dissolution of the additive in the polymer led to decreased crystallinity, but also to decreased mobility of amorphous molecules. Stiffness and strength, but also deformability increased as a result. Above 2 wt% the additive forms a separate phase leading to the deterioration of properties. The success of the approach represents a novel way to control oxygen permeation in EVOH and in other polymers with similar functional groups capable of strong interactions.
Stabilization of polymer material continues to be an important technical field with lot of industrial and scientific attention. Future developments in the field of polymer stabilization need to reflect the corresponding economical requirements. However, ecological requirements start to play increasingly important role in development of stabilization packages for polymers. Present theoretical understanding of polymer degradation and stabilization principles does not yet sufficiently cover the full chemical and physical complexity of polymer stabilization, and therefore it can be expected that most of new developed stabilizers and stabilization systems in near future would be still based on accumulated practical experience and existing empirical know-how.
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