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RHEOLOGY OF LIQUID POLYBUTADIENES
M. PEKAŘ, P.KOPECKÝ
Faculty of Chemistry, Technical University of Brno, Purkyňova 118, CZ-612 00 Brno, Czech Republic
Liquid polybutadienes, pure or end-capped by various functional groups, are resins of versatile use. They turn into the solid state either by crosslinking through the double bonds or by reactions of the functional groups. In the latter, polybutadiene polyols for the synthesis of special polyurethanes may serve as an example. Liquid polybutadienes have started to be produced also in the Czech Republic by Kaučuk company under the trade name Krasol.
This contribution present first results of rheological study of these new materials. Scope of this study was to characterize Krasol polybutadienes from the rheological point of view and examine their rheological behavior relevant for their applications in polyurethane preparations. Measurements were performed on HAAKE RS100 rheometer.
Flow curves of pure and a ,w -dihydroxy polybutadiene were measured at several temperatures and several molecular weights. Typical newtonian behaviour was observed.
Mixtures of a ,w -dihydroxypolybutadiene with glycerol or 2-ethyl-1,3-hexanediol in various concentrations were prepared. The former is used as a polyurethane crosslinker and is unmiscible with polybutadiene. The latter is polyurethane chain extender and much more miscible. Flow curves of these mixtures were measured at laboratory temperatures to obtain information on the relation between liquid phase behaviour and flow properties.
Curing kinetics of polybutadiene-based polyurethanes was investigated using oscillatory rheological measurements in time domain with constant frequency and strain. Studied mixtures differed in the miscibility of their constituents and content of polyurethane hard segments (crosslinker concentration). Influence of these parameters on the crosslinking course and final network was discussed.
Polyurethane compositions with lower than stoichiometric amount of isocyanate were also prepared in order to test the rheological behaviour of forming network in various states of curing degree.
M. S. Araújoa, A. L Simalb, B. V. Koktac
aDepartment of Materials Engineering, Universidade Estadual de Ponta Grossa, Paraná, Brazil
bDepartment of Materials Engineering, Universidade Federal de Sao Carlos, Sao Paulo, Brazil
cDepartement of Chemical Engineering, Université du Québec a Trois-Rivieres,Trois-Rivieres, Québec, Canada
In general, the thermoplastic composites of cellulose give an increase of Young's modulus proportional to the concentration of cellulose when compared to the polymer matrix. Meanwhile, the elongation at break and the resistance to impact decrease . In order to improve the toughness of the composites based on LLDPE and cellulose fibers, liquid polybutadiene (LPB) and isocyanate terminated polybutadiene (ITPB) were studied as agents to improve the impact resistance. Also, the dicumyl peroxide (DCP) was used as an initiator for reactions involved in the process. Both polybutadienes demonstrated to be effective in the improvement of the toughness and in the impact resistance. Although the composite based on the PBL showed higher elongation performance than the ITPB; it reached a lower impact resistance (Fig. 1 and 2). Also, it was observed that the DCP has a very important role in the toughening process of the ITPB, i.e., it maintains the Young's modulus, increases the impact resistance and improves the toughness. In order hand, DCP decreases the impact resistance and the toughness of the composites based on LPB. It seems that the ITPB is also working as compatibilizer agent, improving the yield stress of composites. This improvement is even greater when the DCP is used together with the ITPB. In the case of LPB, the DCP should not be added to the composition, since it is decreasing the mechanical properties of the composite at least within the studied concentrations.
Fig.1 : Impact resistance of composites based on LLDPE, cellulose fibers, dicumyl peroxyde (DCP) and liquid polybutadiene (LPB).
Fig. 2 : Impact resistance of composites based on LLDPE, cellulose fibers, dicumyl peroxyde (DCP) and isocyanate terminated polybutadiene (ITPB).
Peter Jandura1, Bohuslav V. Kokta1 and Bernard Riedl2
1Pulp and Paper Research Center, University of Quebec, C.P. 500, Trois-Rivieres, Quebec, Canada G9A 5H7
2Centre for Research on Science and Engineering of Macromolecules, Wood Science, Faculty of Forestry, Laval University, Quebec, Canada G1K 7P4
Unsaturated and saturated organic acids with 11 and 18 carbon atoms respectively were used to prepare fibrous cellulose esters (CEL-EST) with different degrees of substitution (DS) in the Pyridine/Toluenesulphonylchloride (Py/TsCl) system. High bleached sulfite cellulose fibers were esterified at one (A) and two (B) hours of reaction time with following acids: undecylenic acid (UNA), undecanoic acid (UNC), oleic acid (OLA) and stearic acid (STA).
Fig. 1. 13C-NMR numeration of the carbon atoms in cellulose and in long chain organic acid cellulose esters
The chemical structures of CEL-EST were identified by solid state CP/MAS 13C-NMR (75.3 Mhz) and the substitution reaction was confirmed by diffuse reflectance infrared spectroscopy FTIR-DRIFT. In all cases the heterogeneous esterifications yielded in partially substituted insoluble cellulose esters retaining their fibrous structure. 13C-NMR cellulose carbons resonance intensities ratios (C/C') as the indicators of changes in crystalline/amorphous region in CEL-EST were correlated with their DS. Infrared carbonyl (C=O) absorption band in Kubelka-Munk mode was selected to measure the extent of the modification and the correlation against the percent of acido groups (%AG) in CEL-EST was examined.
Fig. 2. Crystalline/amorph carbon ratios [C/C'] versus Degree of substitution. (A) CEL, (B) CEL-UNA-A, (B*) CEL-UNA-B, (C) CEL-UNC-A, (C*) CEL-UNC-B, (D) CEL-OLA-A, (D*) CEL-OLA-B, (E) CEL-STA-A, (E*) CEL-OLA-B.
Peter Jandura1, Bohuslav V. Kokta1 JANA MIKESOVA2 and Bernard Riedl3
1Pulp and Paper Research Center, University of Quebec, C.P. 500, Trois-Rivieres, Quebec, Canada G9A 5H7
2Institute of Macromolecular Chemistry, Academy of Science of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic
3Centre for Research on Science and Engineering of Macromolecules, Wood Science, Faculty of Forestry, Laval University, Quebec, Canada G1K 7P4
In cellulose fibers thermoplastic composites when dealing with compatibility phenomena a modification of cellulose fibers by organic acids through the esterification can be employed in order to change the hydrophilic character of cellulose fibers and prepare their surface more compatible with that of hydrophobic polymer. Especially, unsaturated bonds present on the chain of an organic acid could be of further interest as the active sites for grafting of polymer chains onto cellulose surface during compounding.
An experimental study was carried out to investigate the effect of different fibrous long-chain organic acid cellulose esters (CEL-EST) on the rheological behavior and tensile properties of cellulose fibers - polyethylene composites. Linear low-density polyethylene (PE) was used as polymer matrix. CEL-EST used were cellulose undecylenate (CEL-UNA), cellulose undecanoate (CEL-UNC), cellulose oleate (CEL-OLA) and cellulose stearate (CEL-STA). Dicumyl peroxide (DCP) was used as an initiator. It was found that the addition of CEL-EST to the CEL+PE composites affected rheological behavior of the melts and tensile properties of composites quite differently. For example the addition of CEL-OLA-B decreased the melt viscosity and increased the strength and energy at yield point of composites in comparison with polyethylene matrix filled only with cellulose fibers (PE+CEL). However there was no effect of the addition of CEL-STA-B on either the tensile or rheological properties of composites.
Fig. 1. Viscosity vs. frequency for CEL-EST/CEL - PE composites without an initiator. CEL-EST represents %wt within 30% of a total fiber content in PE matrix.
Yongsok SEOa, b, Hyuk YUb, KWANG UNG KIMa
a Polymer Processing Laboratory, Korea Institute of Science and Technology (KIST), P.O.Box 131, Cheongryang, Seoul, Korea
b Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, WI53706, U.S.A.
Using the surface quasi-elastic light scattering technique, we have studied the monolayer behavior of diblock copolymers of polystyrene(PS) and poly(methyl methacrylate) (PMMA) at the air/water interface in terms of surface viscoelasticity. Diblock copolymers have a similar molecular weight of polystyrene but differ in the molecular weight of PMMA segment. The frequency shift measurement shows that a biphasic state in PMMA moiety exists, which is in accord with other's observation using a neutron reflectometry. Damping coefficient undergoes broad maximum at a concentration where the surface pressure is still zero and then rapidly decreases with increasing concentration (hence decreasing surface area). This is related to the fact that the reduced elasticity exceeds the point of optimum resonance between the surface modes. These are manifest with a block copolymer having a longer PMMA segment.
The dynamic longitudinal elasticity and the corresponding viscosity were calculated from the frequency shift and the corrected width measurements with an assumption that the transverse viscosity is zero. The surface elasticity values show a maximum at the collapsing pressure, which indicates that the surface becomes very rigid. High molecular weight polymer deviates from the static elasticity values at much lower concentration. The surface viscosity values are also quite large. The values of the frequency-multiplied surface viscosity is as much big as the surface elasticity indicating that the monnolayer surface dissipates as much energy as it accepts. Hence, the monolayer shows the behavior of a high modulus film. Dilational surface viscosity increases more rapidly with the concentration for higher molecular weight polymer.
In the pole plot, the monolayer shows a transition from the pure liquid dynamics to the purely viscous film by way of the infinite lateral modulus. The pole figure of longer chain reveals that strong interaction between molecules leads to heterogeneous films with patches of very condensed monolayer possessing infinite lateral modulus and those of pure liquid dynamics. This is consistent with neutron relectometry results. The departue from the Kelvin limit appears at lower surface concentration (larger surface area) for the high molecular weight polymer. This is in accord with the surface viscoelastic properties.
P.ROMISZOWSKI, A.SIKORSKI
Department of Chemistry, University of Warsaw
Pasteura 1, 02-093 Warszawa, Poland
Monte Carlo simulations of lattice star-branched polymers in diluted solution confined between two parallel repulsive walls were performed. The polymers consisted of 3 branches of equal length n=16,33,66 and 133 segments. The dynamics of the system was simulated by employing the set of micromodifications to each element of the chain on a simple cubic lattice. The quality of the solvent has been varied from good solvent (athermal solution) to a bad solvent (collapsed globule regime). The changes of the solvent quality enabled one to mimic the temperature dependence of the properties of the polymer solution. The distance between the plates has been changed enabling one to observe the transition from almost 2-dimension scale to the fully 3-dimensional objects.
The static and dynamic properties of the system have shown that the distance between the plates has an influence on the dimensions of the molecules. The effect of a deformation of the molecule by the plates has been observed and discussed, especially the possible changes in the mechanism of chain motion have been discussed. Also the effect of the plate distance on dynamics of the system has been described. The short-time dynamics (center-to end relaxation times) as well as long-time dynamics (self-diffusion) have been investigated and discussed.
A MONTE CARLO STUDY
A.SIKORSKI, P.ROMISZOWSKI
Department of Chemistry, University of Warsaw
Pasteura 1, 02-093 Warszawa, Poland
Monte Carlo simulations of simple models of branched polymers were carried out. The model chains were confined to simple cubic lattice and consisted of f = 3 branches of equal length. The total number of polymer segments varied from N =49 up to 799. The simulations were performed by employing the set of local micromodifications of the chain conformations. The model chains were athermal, i.e. good solvent conditions were modeled. The density of grafted chains on the surface was varied from a single chain up to 0.3.
The influence of the branching on the static and dynamic properties of the system studied was shown. The differences between linear and branching polymer brushes were pointed out. The relation between the structure and short-time dynamics (relaxation times) was discussed.
A.HAVRÁNEK
Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, Prague, V Holešovičkách 2, CZ-180 00 Praha 8, Czech Republic
The flow of a large molecule through a gel is a very complicated process which cannot be adequately described by standard hydrodynamic models. In this flow a special type of motion appears which has been denoted geometration by Deutsch [1] as it is similar to the motion of inchworms of the family of Geometridae which move by alternately bunching up and extending. The geometration of DNA through a gel has been several times directly detected by fluorescent microscopy.(e.g. [2]). If a large molecule in the coil conformation contacts the gel fibre it is hooked around it The force which drives the molecule (e.g. the electric force in electrophoresis) at first elongates the arms of the hooked molecule. Afterwards, one of the arms wins in a tug-of-war, the whole molecule slip off the fibre, and the molecule gradually obtains again the conformation of a statistical coil.
Microrheology of geometration is studied. It is similar to that used in the reptation model concept of molecular hydrodynamics. Nevertheless, it seems to be necessary not to omit the inertia forces in the description. The neglecting of inertia forces in molecular hydrodynamics is very usual. The Newton equation of motion is replaced by the Langevin equation. This is done e.g. in the well known theories of Rouse or Zimm. We try to give an equation of motion of the Newtonian type describing geometration. It contains a quasi-inertia term by which some special features of the motion of a large molecule through a gel may be explained. One such feature is observed in DNA preparative electrophoresis performed in polymeric gels: the frequency and chain length dependent large fractionation activity observed in the field inversion electrophoresis (e.g. [3]). We hope that the microrheological study of the motion of a large molecule through a gel may give also some new viewpoints to the gel permeation chromatography.
DINO FERRI, LEONARDO CASTELLANI
ENICHEM Research Center, Via Taliercio 14, 46100 Mantova, Italy
The phenomenology of the glass transition (GT) and flow transition (FT) relaxation processes of polystyrene, styrene-acrylonitrile and a-methylstyrene-acrylonitrile copolymers is investigated by means of both dynamic-mechanical and dielectric spectroscopy in the linear response region.
The temperature dependence of the average relaxation time t of the two processes follows a
Vogel-Tammann-Fulcher (VTF) equation: 
. The flow and glass transitions exhibit
different VTF parameters, reflecting the different length and
time scales involved in the two processes. The different
relaxation mechanisms, involving different parts of the polymer
chain, exhibit an appreciably different temperature sensitivity.
This different response vitiates time-temperature
superpositioning giving rise to complex thermorheological
behavior in the glass transition zone. This finding further
confirms Donth and Ngai models.
A comparison between dynamic-mechanical and dielectric relaxation times, tmech and tdiel, in the glass transition zone highlights a profound difference in the time scale explored by the two techniques. A temperature indipendent gap betweeen tmech and tdiel is observed, revealing that segmental motions contributing to the dielectric relaxation are faster than those observed mechanically. This finding suggests a scaling law for the decay function f(t) of the glass transition of the form f(t)=g[t/t(T)] where g is temperature independent. The attention is then focused on particular relationships between the VTF parameters for GT and FT relaxation of the same polymer and for the same relaxation process of different polymers. Two coupled relationships are systematically found of the form:
and:
These relationships suggest a universal feature underlying the character of the VTF equation.
M. HUSKIĆ
National Institute of Chemistry, Hajdrihova 19, Ljubljana, Slovenia,
Lignin is the second most abudant renewable polymer resource. Unfortunately, its physical properties make lignin useless as a building or constructing material. The pulp and paper industry produces very large quantities of lignin. It is used for several purposes, but still the used quantities remain small. Approximately 90% of lignin is burned to recover energy. Many extensive studies have been made on the transformation of lignin into an useful polymeric material. Lignin was considered as as a filler in unsaturated polyester (UP) resins or as a component to make crosslinked polyesters. UP resins in which lignin is used as a component and not only a filler showed large increases of viscosity.
UP resins containing up to 10% of lignin were prepared and their rheological properties were determined by rotational viscosimetry. The resins exhibit extensive shear thinning behaviour at shear rates up to 50 s-1. At shear rates 50-190 s-1 the drop of viscosity is minimal. The viscosity of lignin based UP is significantly higher while shear thinning is lower. The viscosity of UP resin containing 2.5% of lignin is 13% higher at the shear rate 19 s-1 and 22-23% higher at shear rate 50-190 s-1. Increasing lignin content in UP above 2.5% had a smaller effect on viscosity increase. The viscosity of UP resin containing 10% of lignin is only 28% (19 s-1) - 50% (50-190 s-1) higher.
KAREL JELÍNEK, ZUZANA LIMPOUCHOVÁ AND KAREL PROCHÁZKA
Department of Physical and Macromolecular Chemistry, Charles University in Prague, Albertov 2030, 128 40 Prague 2
Block copolymers containing a long hydrophobic (e.g., polystyrene, PS,) and a long polyelectrolyte block (e.g., poly-2-vinylpyridine, PVP) do not dissolve in aqueous solvents. However, polymolecular micelles with compact PS cores and PVP shells may be prepared indirectly by dialysis from organic solvent-water mixtures into acid aqueous solutions. The PS-PVP micelles are stable in acid solutions and precipitate at high pH. An addition of a linear poly(2-vinylpyridine)-block-poly(ethylene oxide), PVP-PEO, leads to the stabilization of the original micelles at high pH in the form of "onion-skin" micelles.(ref.1)
"Onion-skin" micelles, OSM, are spherical polymeric nanoparticles containing several segregated polymeric layers. The middle layer of the three-layer micelle is formed by collapsed and strongly interpentrated PVP blocks, both from PS-PVP and PVP-PEO. The formation of OSM is usually reversible with pH which suggests interesting new applications, e.g., in environmental chemistry and biomedicine. Despite the potential applicability of OSM, very little is know concerning the chain conformations, especially in the collapsed middle layer.
In this communication, we report on our latest Monte Carlo computer simulations that are aimed to yield information on the conformational behavior of collapsed blocks in the middle layer.
[1] Procházka K., Martin T. J., Webber S. E., Munk P.:Macromolecules 29, 6526 (1996)
