Polymer/layered silicate nanocomposites: a review from preparation to processing

Biodegradable polymers and their layered silicate nanocomposites: In greening the 21st century materials world

The use of polymer modified asphalts for waterproofing and in road pavement has been continually increasing worldwide, because a relatively small quantity of added polymer can significantly enhance performance and durability. The knowledge of the morphological structure of such materials is still incomplete and controversial, mainly because of the compositional complexity. In practice, rheology is one of the most useful tools for the study of polymer modified asphalt. Particularly, nonlinear rheology may give unique information that helps to interpret how the polymer organizes when it is blended with asphalt. In this paper, besides a brief description of linear rheological properties and modeling, particular attention is paid to the most recent studies on the structure and to material functions, such as shear viscosity and relaxation modulus in the nonlinear viscoelastic region. The correlation of nonlinear behavior with polymer characteristics and with the architecture established when polymers are blended with asphalts is then described.

Relation between polymer architecture and nonlinear viscoelastic behavior of modified asphalts

Polypropylene (PP)/clay nanocomposites (PPCNs) were autoclave-foamed in a batch process. Foaming was performed using supercritical CO 2 at 10 MPa, within the temperature range from 130.6°C to 143.4°C, i.e., below the melting temperature of either PPCNs or maleic anhydride-modified PP (PP-MA) matrix without clay. The foamed PP-MA and PPCN2 (prepared at 130.6°C and containing 2 wt% clay) show closed cell structures with pentagonal and/or hexagonal faces, while foams of PPCN4 and PPCN7.5 (prepared at 143.4°C, 4 and 7.5 wt% clay) had spherical cells. Scanning electron microscopy confirmed that foamed PPCNs had high cell density of 10 7 -10 8 cells/mL, cell sizes in the range of 30-120 μm, cell wall thicknesses of 5-15 μm, and low densities of 0.05-0.3 g/mL. Interestingly, transmission electron microscopic observations of the PPCNs' cell structure showed biaxial flow-induced alignment of clay particles along the cell boundary. In this paper, the correlation between foam structure and rheological properties of the PPCNs is also discussed.

Foam processing and cellular structure of polypropylene/clay nanocomposites

We use a new extensional rheology test fixture that has been developed for conventional torsional rheometers to measure the transient extensional stress growth in a number of different molten polyethylene samples including a linear low density polyethylene (Dow Affinity PL 1880), a low density polyethylene (Lupolen 1840H), and an ultrahigh molecular weight polyethylene (UHMWPE). The transient uniaxial extensional viscosity functions for the linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) samples have both been reported previously in the literature using well-established instruments and this allows us to benchmark the performance of the new test fixture. Transient stress growth experiments are carried out over a range of Hencky strain rates from 0.003 to 30s−1 and the data show excellent agreement with the published material functions. At deformation rates greater than 0.3s−1 a true steady state extensional viscosity is not obtained in the LDPE samples due to the onset of neckin...

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Measuring the transient extensional rheology of polyethylene melts using the SER universal testing platform

Polymer melt elongation is one of the most important procedures in polymer processing. To understand its molecular mechanisms, we constructed an elongational flow opto-rheometer (EFOR) in which a high precision birefringence apparatus of reflection-double path type was installed into a Meissner's new elongational rheometer of a gas cushion type (commercialized as RME from Rheometric Scientific) just by mounting a small reflecting mirror at the center of the RME's sample supporting table. The EFOR enabled us to achieve simultaneous measurements of tensile stress σ(t) and birefringence Δn(t) as a function of time t under a given constant strain rate 
$$\dot \varepsilon _0$$

 within the range of 0.001 to 1.0s−1. σ(t) can be monitored upto the maximum Hencky strain ɛ(t) of 7 as attained, in principle, with RME, while the measurable range of the phase difference in the birefringence was 0 to 250 π (0 to 79 100 nm for He-Ne laser light) within the accuracy of ±0.1 π (±31.6 nm) up to ɛ(t) ∼ 4. The performance was tested on an anionically polymerized polystyrene (PS) and a low density polyethylene (LDPE). For both polymers σ(t) first followed the linear viscoelasticity rule in that the elongational viscosity, 
$$\eta _E (t) \equiv \sigma (t)/\dot \varepsilon _0$$

 , is three times the steady shear viscosity, 3η
o(t), at low shear rate 
$$\dot \gamma$$

 , but the η
 E
 (t) tended to deviate upward after a certain Hencky strain 
$$\varepsilon (t) = \dot \varepsilon _0 t$$

 was attained. The birefringence Δn(t) was a function of both Hencky strain 
$$\varepsilon (t) = \dot \varepsilon _0 t$$

 and strain rate 
$$\dot \varepsilon _0$$

 in such a way that the stress-optical law holds with the stress-optical coefficient C(t) = Δn(t)/δ(t) being equal to the ones reported from shear flow experiments. Interestingly, however, for PS elongated at low strain rates the C(t) vs σ(t) relation exhibited a strong nonlinearity as soon as σ(t) reached steady state. This implies that the tensile stress reaches the steady state but the birefringence continues to increase in the low strain-rate elongation. For the PS melt elongated at high strain rates, on the other hand, C(t) was nearly a constant in the entire range observed. For LDPE with long-chain branchings, σ(t) exhibited tendency of strain-induced hardening after certain critical strain, but C(t) was nearly a constant in the entire range of σ(t) observed.

Elongational flow opto-rheometry for polymer melts : 1. Construction of an elongational flow opto-rheometer and some preliminary results

Elongational flow and birefringence of low density polyethylene and its blends with ultrahigh molecular weight polyethylenet

Elongational flow-induced morphology change of block copolymers. 2. A polystyrene-block-poly(ethylene butylene)-block-polystyrene triblock copolymer with cylindrical microdomains

Elongational flow-induced morphology change of block copolymers. Part 1. A polystyrene-block-poly(ethylene butylene)-block-polystyrene-block-poly(ethylene butylene) tetrablock copolymer with polystyrene spherical microdomains

Akira Kojima

Papers

Elongational flow opto-rheometry for polymer melts : 1. Construction of an elongational flow opto-rheometer and some preliminary results

Elongational flow and birefringence of low density polyethylene and its blends with ultrahigh molecular weight polyethylenet

Elongational flow-induced morphology change of block copolymers. 2. A polystyrene-block-poly(ethylene butylene)-block-polystyrene triblock copolymer with cylindrical microdomains

Elongational flow-induced morphology change of block copolymers. Part 1. A polystyrene-block-poly(ethylene butylene)-block-polystyrene-block-poly(ethylene butylene) tetrablock copolymer with polystyrene spherical microdomains