Preparation of interconnected poly(\u3b5-caprolactone) porous scaffolds by a combination of polymer and salt particulate leaching

This paper examines a new technique for the preparation of porous scaffolds by combining selective polymer leaching in a co-continuous blend and salt particulate leaching. In the first step of this technique, a co-continuous blend of two biodegradable polymers, poly(\u3b5-caprolactone) (PCL) and polyethylene oxide (PEO), and a certain amount of sodium chloride salt particles are melt blended using a twin screw extruder. Subsequently, extraction of the continuous PEO and mineral salts using water as a selective solvent yields a highly porous PCL scaffold with fully interconnected pores. Since, the salt particles and the co-continuous polymer blend morphology lead to very different pore sizes, a particular feature of this technique is the creation of a bimodal pore size distribution. Scanning electron microscopy, mercury intrusion porosimetry and laser diffraction particle size analysis were carried out to characterize the pore morphology. The prepared scaffolds have relatively homogeneous pore structure throughout the matrix and the porosity can be controlled between 75% and about 88% by altering the initial volume fraction of salt particles and to a lesser extent by changing the PCL/PEO composition ratio. Compared to the conventional salt leaching technique and to its different variants, the proposed process allows a better interconnection between the large pores left by the salt leaching and a fully interconnected porous structure resulting from the selective polymer leaching. The average compressive modulus of the different porous scaffolds was found to decrease from 5.2 MPa to about 1 MPa with increasing porosity, according to a power\u2013law relationship. Since, the blending and molding of the scaffold (prior to leaching) can be made using conventional polymer processing equipment, this process seems very promising for a large scale production of porous scaffold of many sizes and in an economic way.Peer reviewed: YesNRC publication: Ye

Non-Fluorinated Proton Exchange Membranes Based on Melt Extruded SEBS/HDPE Blends

Peer reviewed: YesNRC publication: Ye

Continuity development in polymer blends of very low interfacial tension

Phase continuity development and co-continuous morphologies are highly influenced by the nature of the interface in immiscible polymer blends. Blends of ethylene\u2013propylene\u2013diene terpolymer (EPDM) and polypropylene (PP) possess an interfacial tension of about 0.3 mN/m and provide an interesting model system to study the detailed morphology development in a very low interfacial tension binary system. A variety of blends with viscosity ratios of 0.2\u20135.0 and shear stresses of 11.7\u2013231.4 kPa were considered. Using a variety of sophisticated morphology protocols it is shown that at low blend compositions, the dispersed phase actually exists as stable fibers of extremely small diameter of 50\u2013200 nm and the continuity develops by fiber\u2013fiber coalescence. An analysis using break-up times from Tomotika theory also supports the notion of highly stable dispersed fiber formation. These results challenge the current view of the dispersed phase as small spherical droplets. It is shown, under these conditions, that a seven-fold variation in the viscosity ratio has virtually no influence on%continuity or morphology, while a large change in the matrix shear stress from 11.7 to 90.9 kPa has an important effect on pore diameter. Both sides of the continuity diagram are studied and highly symmetrical continuity behavior is observed with composition. In fact a single master continuity curve is observed for these blends varying in viscosity ratio from 0.7\u20135.0 and with shear stresses from 11.7\u201390.9 kPa. Although the glass transition temperatures indicate that these materials are completely immiscible after melt mixing and cooling, it is shown that the blends demonstrate the morphological features of a partially miscible system. These results support a concept that the blend was partially miscible during melt blending, at which time the gross morphological features of the blend were developed, but becomes fully phase separated upon cooling. It appears that the quenching of the EPDM/PP blend from the melt is rapid enough to preserve the imprint of that partial miscibility on the gross blend morphology.Peer reviewed: YesNRC publication: Ye

Comparison of sorbitol and glycerol as plasticizers for thermoplastic starch in TPS/PLA blends

This article investigates the structure and properties of thermoplastic starch/PLA blends where the TPS phase is plasticized by sorbitol, glycerol, and glycerol/sorbitol mixtures. The blends were prepared using a twin-screw extruder where starch gelatinization, water removal, and dispersion of TPS into a PLA matrix were carried out sequentially. The plasticizers were added to starch in the first stage of the extruder to allow complete starch gelatinization. The PLA was added at mid-extruder and thoroughly mixed with the TPS. The plasticizer concentration was varied from 30 to 42% and the TPS content was varied from 27 to 60% on a weight basis. In all investigated blends, the PLA formed the continuous phase and the TPS was the dispersed phase. The viscosity, blend morphology, tensile mechanical properties as well as the thermal properties of the materials were measured. It was found that the glycerol/sorbitol ratio has an important effect on the blend properties. Finer blend morphologies, higher tensile strength and modulus but lower crystallization rate were found for the sorbitol plasticized blends.NRC publication: Ye

Preparation and properties of extruded thermoplastic starch/polymer blends

This article examines the starch gelatinization and the blend morphology development in blends of thermoplastic starch (TPS) with high-density polyethylene, polypropylene, polystyrene, poly(lactic acid), and polycaprolactone. The TPS gelatinization and mixing with the second polymer was carried out on a twin-screw extrusion process, where the starch was sequentially gelatinized, devolatilized, and then mixed in the molten state with a synthetic polymer. The role of excess water and process temperature on starch gelatinization was assessed by measuring the X-ray scattering. All prepared blends included 25 % TPS that was dispersed in the synthetic polymer matrix. Compatibilized versions of these same blends were obtained by partially substituting the polymer matrices with maleated analogs. The blend morphology was probed by scanning electron microscopy. Complete starch gelatinization was obtained when the gelatinization process was carried out over 100\ub0C regardless of amount of water used as co-plasticizer. The blend morphologies were greatly improved when a maleated compatibilizer was added. Only TPS/PCL blends exhibited a finely dispersed TPS phase without the use of a compatibilizer. In general, the addition of the TPS reduced slightly the tensile modulus and strength of the different polymers and more importantly the elongation at break.Peer reviewed: YesNRC publication: Ye

Nucleation and Crystallisation of PLA

Peer reviewed: YesNRC publication: Ye

Biaxial orientation and properties of polylactide/thermoplastic starch blends

The biaxial stretchability and film properties of polylactide/thermoplastic starch blends were investigated. Polylactide (PLA) and thermoplastic starch (TPS) were blended in various proportions. Blends containing 33 and 67 wt.% TPS were prepared via a twin-screw extrusion process. Water, glycerol and sorbitol were used as plasticizers. Interfacial modification was performed by grafting the PLA with maleic anhydride. A chain extender was also used. These blends were subsequently cast into sheets and biaxially drawn using a laboratory biaxial stretcher. The structural properties and mechanical performance were evaluated. The addition of the grafted PLA and chain extender yielded a much finer TPS dispersed phase, which was preferentially oriented in the direction of flow. The addition of TPS, grafted PLA and chain extender affected the biaxial stretchability of the neat PLA. The tensile properties for both cast sheets and biaxial films were evaluated as a function of process parameters and composition of the blends. Adding TPS to PLA resulted in a decrease of the tensile modulus and strength but increased the elongation at break in some cases.Peer reviewed: YesNRC publication: Ye