Porous materials from crystallizable polyolefins produced by gel technology

Abstract

A new method for obtaining porous and porous fiber polymers is presented. This method is based on using gel‐type technology (without previously preparing polymer solutions) for crystallizable polymers, preparing polyethylenes, and including polyethylenes of very high molecular mass and isotactic polypropylene. The method consists in swelling crystalline polymer films at elevated temperatures in a proper solvent with subsequent precipitation with a non‐solvent at different conditions. In this case, simultaneous or consecutive processes of phase separation of amorphous or/and crystalline type occurs; stretching the sample can also accompany this process. Complete phase diagrams of two‐ and three‐component systems (polymer‐solvent and polymer‐solvent precipitator) were constructed. Temperature‐concentration boundaries of amorphous separartion (binodal) and crystallization (liquidus) are reported for the system polyethyleneo‐xylenedimethyl formamide. Phase transitions of both types influence characteristics of the resultant porous structure. They were prepared by simultaneous (precipitation of a gel by dimethyl formamide at 25°C) or consecutive (precipitation with a hot non‐solvent at 138°C and following cooling) phase separation. Studied were the effect of experimental conditions (temperature, times for solvation and precipitation, polymer molecular mass, the thermodynamic quality of solvents and parameters of film stretching) on peculiarities of the structure and quantitative characteristics of final porous and fiber‐porous polyolefins. It has been demonstrated that the method proposed allows us to obtain a crystalline and highly porous polymer with open poros, a bimodal size distribution and with a highly developed inner surface. Further high strength and small shrinkage are characteristic of the fiber‐porous materials. The method under discussion appears to be universal, it does not require a preliminary preparation of polymer solutions and can be realized within a general technology of polymer films and sheet processing. Highly porous polymers obtained by this technology, primarily based on polyethylenes of very high molecular mass, can be used as neutral supports for multi‐functional membranes, polymeric covers, frame systems for implants and other applications.

Acrylic-Based Materials for Biomedical and Bioengineering Applications

“…The interconnection and geometry of pores depend primarily on the tissue to be regenerated which then provide information on the desired physicochemical properties and mechanical resistance of the material. Several methods and techniques have been reported to produce scaffolds: gas foaming [118], fibre meshes sintering [119], solvent casting [120], polymerisation in solution [101,121,122], porogen leaching method [123,124], freeze-drying methods [125,126], electrospinning [127], 3D printing [128], 3D bioplotting of scaffold and cells [129], etc. For instance, acrylic scaffolds with interconnected spherical pores and controlled hydrophilicity were synthesised using a template of sintered PMMA microspheres of controlled size.…”

Latest Improvements of Acrylic-Based Polymer Properties for Biomedical Applications

“…The interconnection and geometry of pores, which depend on the tissue to regenerate, physicochemical properties and mechanical resistance of the material, play in these biomedical applications a major role. Thus, there are several methods to produce scaffolds, which include gas foaming [100], sintering fiber meshes [101], solvent casting [102], polymerization in solution [80,103], porogen technique [104,105], freeze-drying techniques [106,107], electrospinning [108], 3D printing [109], 3D bioplotting of scaffold with cells [110], etc. For example, acrylic scaffolds with interconnected spherical pores and controlled hydrophilicity with interconnected porous structure were synthesized using a template of sintered PMMA microspheres of controlled size.…”

Three‐dimensional nanocomposite scaffolds with ordered cylindrical orthogonal pores

“…In general these layouts are dictated by the mechanical and functional requirements of the different specialized tissues. There are several methods to produce scaffolds, which include gas foaming,1 sintering fiber meshes,2 solvent casting,3 and others 4, 5. Different kinds of porogenic agents and ways to induce porous architectures have been reported;2, 6, 7 each has some advantages and some disadvantages with respect to matters such as the control of the pore size, pore distribution, interconnectivity, and construction of channels within the scaffold to guide cell growth.…”