Authors:F. Cser, M. Jollands, P. White, and S. Bhattacharya
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.
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,
withTg values around −30‡C.
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.
Authors:A. Marcilla, A. Gómez-Siurana, and S. Menargues
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.
In order to provide additional information on the miscibility of the PVC/EVA system, calorimetric parameters such as ΔCpi,Tgi and ΔTgi 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
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.
Authors:X. Cai, H. Shen, C. Zhang, Y. Wang, and Z. Kong
A simple operation mode to determine the apparent activation energy Ea is introduced. Ea 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.
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
Authors:L. Bernazzani, C. Cardelli, G. Conti, and P. Gianni
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.