Search Results

You are looking at 1 - 10 of 1,230 items for :

  • All content x
Clear All

Abstract  

Cross-linked polymers have particular rheological responses during reprocessing, e. g. if the material is recycled, special processing conditions are required. Other virgin polymers can be used as a blending component to enhance rheological properties. Bi-layer film of EVA/LLDPE was produced on a blown film line and cross-linked by high-energy radiation. This film was ‘agglomerated’ then reprocessed in a twin-screw extruder with virgin LLDPE and blown into film. The miscibility of the blend components was then studied using a TA Instruments temperature modulated differential scanning calorimeter (TMDSC). It was found that the cross-linked EVA/LLDPE scrap and the LLDPE have a slight miscibility in the liquid state. A bigger portion of LLDPE was miscible (dissolved) in EVA in low LLDPE blends. A positive deviation in the heat capacity of the LLDPE component compared to the additivity rule indicated melting to be more reversible in the first heating cycle. This initial miscibility was attributed to being induced by high shear during processing. A smaller positive deviation also occurred in the second heating cycle. This was attributed to intrinsic miscibility.

Restricted access

Abstract  

The properties of polymeric blends originate from the synergistic association of their components. In this investigation, phenolic resins obtained by the reaction of cashew-nut shell liquid (CNSL) and aldehyde are used in several applications. Mixtures of CNSL with industrial reject ethylene-co-vinyl acetate (EVA reject) were prepared with an EVA reject content up to 70%. The thermal compatibility and stability were evaluated by means of thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). For blends containing a high percentage of EVA reject, the TG curves clearly show two decomposition stages, one at 350‡C and the other at 450‡C (onset 467‡C). The DIG curves of the blend containing 70% CNSL exhibit decomposition at 240‡C. The DSC curves show that the samples containing a high percentage of EVA reject are incompatible, withT g values around −30‡C.

Restricted access

Abstract  

Thermal stability and degradation processes in PVC/EVA systems were evaluated for a series of EVAs with different vinyl acetate contents. The experimental data revealed a relationship between the thermogravimetric curves and the degree of interaction in the mixtures as compared to the pure polymers, which is consistent with the results of microscopic analysis. Kinetic parameters and lifetime data on the mixtures were also calculated.

Restricted access

Oxidative degradation of EVA copolymers in the presence of catalysts

Comparison among different zeolites and related materials

Journal of Thermal Analysis and Calorimetry
Authors: A. Marcilla, A. Gómez-Siurana, and S. Menargues

Abstract

A study of the catalytic degradation of EVA copolymers under air atmosphere has been carried out using thermogravimety (TG). Three commercial EVA copolymers and five zeolites and related materials catalysts have been selected. The degradation process in air atmosphere involves four main decomposition steps (as observed in TG), being more complex than the corresponding process in inert atmosphere. The presence of MCM-41, HY and H-β does not seem to noticeably affect to the overall degradation temperature, despite the temperature of maximum reaction rate for the second decomposition step being slightly displaced towards lower temperatures. Contrarily, the presence of HZSM-5 and HUSY zeolites seems to displace the main stage of the oxidative degradation process towards higher temperatures. Moreover, the relative importance of the second and third decomposition step is different depending on the amount and the nature of the zeolite mixed with the EVA sample. The results obtained show that the presence of the catalyst also enhances the formation of the carbonous residue.

Restricted access

* Éva Jakab: Praedicere und cavere beim Marktkauf. Sachmängel im griechischen und römischen Recht. Verlag C. H. Beck, München, 1997. XII + 332 S.

Restricted access

Abstract  

In order to provide additional information on the miscibility of the PVC/EVA system, calorimetric parameters such as ΔC pi,T gi and ΔT gi were obtained with a different approach. A qualitative and quantitative measure of the blend composition at the interface was obtained. This indicated that the domains are rich in each component and the presence of the second component in the phase has little effect on the main chain relaxation. The PVC fraction in the EVA-rich phase is always larger than the EVA fraction in the PVC-rich phase. Positive and small values of the Flory-Huggins interaction parameter were obtained from calorimetric data.

Restricted access

Abstract  

The synergistic effects of zinc oxide (ZnO) with layered double hydroxides (LDH) in ethylene vinyl acetate copolymer/LDH (EVA/LDH) composites have been studied using thermal analysis (TG), limiting oxygen index (LOI), UL-94 tests, and cone calorimeter test (CCT). The results from the UL-94 tests show that the ZnO can also act as flame retardant synergistic agents in the EVA/LDH composites. The CCT data indicated that the addition of ZnO in EVA/LDH system can greatly reduce the heat release rate. The TG data show that the ZnO can increase the thermal degradation temperature and the charred residues after burning.

Restricted access

Abstract  

A simple operation mode to determine the apparent activation energy E a is introduced. E a can be determined with a double-curve method by using a constant reaction rate (CRR) approach of Hi-Res TG. The most appropriate mechanism function f(α) and frequency factor A are determined by a single-curve method when the activation energies provided by the two methods are in good agreement with each other. The deacetylation of EVA copolymer has been used for illustration. Advantages of the CRR are discussed.

Restricted access

Abstract  

When ethylene-vinyl acetate copolymer, EVA, is heated, a two-stage thermal degradation occurs following its melting. The vinyl acetate content of the copolymer was determined to be 43.8% by using TA 2950 and TA 2050 thermogravimetric instruments. TG/FTIR was used to detect the evolved gas. Acetic acid and trans-1-R-4-R'-cyclohexane were the main products evolved from EVA in the first and second stage, respectively. The apparent activation energies were determined for both stages by differential methods.

Restricted access

Abstract  

The miscibility of blends of poly(vinyl-chloride) (PVC) with poly(ethylene-co-vinyl acetate) (EVA) was investigated through analog calorimetry and a group contribution procedure based on the UNIQUAC model. The group contribution parameters quantifying the pair interactions between the structural features of the above polymers were calculated from experimental excess enthalpies of a series of binary mixtures of chlorocompounds, esters and hydrocarbons. Enthalpy data were also collected for the ternary mixtures (2-chloropropane+ethyl acetate+n-heptane) and (2-chlorobutane + methyl acetate+n-heptane), chosen as possible models for the studied macromolecular mixtures. The miscibility window of the PVC-EVA blends is fairly predicted by the group contribution method. It is also acceptably predicted by the enthalpic behaviour of the first ternary set, but only when the latter is calculated with binary data. A slightly narrower miscibility range is predicted by the binary interaction model. The results of these procedures are compared and the higher reliability of the group contribution procedure is emphasized in terms of its capability to reproduce the exact structure of the macromolecules and the non-univocal choice of the model molecules involved in the analog calorimetry approach.

Restricted access