Single Solvent‐Based Film Casting Method for the Production of Porous Polymer Films

A single solvent‐based film casting process for fabricating porous polymer films is developed in this study. The porous film is produced by mixing concentrated polylactic acid (PLA)/chloroform solution (20 wt%) and fresh chloroform solvent is followed by film casting. The average pore sizes of the films produced are seen to increase from 2.1 (±0.1) µm to 6.4 (±0.2) µm with increasing ratio of concentrated PLA solution and fresh solvent from 1:2 to 1:4. Functional groups of PLA after casting into porous film are confirmed via Fourier transform infrared spectroscopy analysis. Cytocompatibility studies (via Alamar Blue assessment) utilizing MG‐63 cells on the porous PLA films reveal an increase in cell metabolic activity up to 8 d postseeding. In addition, these direct cell culture studies show that the porous membranes support cell adhesion and growth not only on the surface but also through the porous structures of the membrane, highlighting the suitability of these porous films in tissue engineering applications.     

Preparation and Enzymatic Degradation of Porous Crosslinked Polylactides of Biomass Origin

To understand the enzymatic degradation behavior of crosslinked polylactide (PLA), the preparation and enzymatic degradation of both thermoplastic (linear) and crosslinked PLAs that have pore structures with different dimensions were carried out. The porous structures of the linear PLA samples were of micro and nanoporous nature, and prepared by batch foaming with supercritical CO₂ and compared with the porous structures of crosslinked PLA (Lait-X) created by the salt leaching method. The surface and cross-sectional morphologies of the porous structures were investigated by using scanning electron microscopy. The morphological analysis of porous Lait-X showed a rapid loss of physical features within 120 h of exposure to proteinase-K enzymatic degradation at 37 °C. Due to the higher affinity for water, enhanced enzymatic activity as compared to the linear PLA porous structures in the micro and nanoporous range was observed.     

Study on the effect of dispersion phase morphology on porous structure of poly (lactic acid)/poly (ethylene terephthalate glycol-modified) blending foams

A methodology for blending foam of poly (lactic acid) (PLA)/poly (ethylene terephthalate glycol-modified) (PETG) was proposed. PLA/PETG blends were prepared through a melt blending method, using multiple functionality epoxide as reactive compatibilizer. The effects of blending ratio and compatibilizer content on the dispersion morphology, molecular structure, mechanical properties, and rheological behavior of PLA/PETG blends were studied. Then PLA/PETG blends were foamed using supercritical CO₂ as physical blowing agent, and their porous structure, pore size, as well as pore density were investigated. The results showed that the mechanical properties and rheological parameters such as melt strength and melt elasticity, as well as the porous structure of the foams dispersion morphology of PLA/PETG blends were affected strongly. The melt elasticity of PLA/PETG blends increased with increasing compatibilizer content. Dispersion phase morphology of PLA/PETG blends also had a significant effect on the pore density of all the samples. The results indicated that homogeneous and finer porous morphology of PLA/PETG foams with high expansion ratio could be achieved with a proper content of compatibilizer in the blends.     

Development of polylactide open‐cell foams with bimodal structure for high‐acoustic absorption

In this study, a highly porous and interconnected foam structure was fabricated using compression molding combined with particulate‐leaching technique. The foamed structures were fabricated with polylactide (PLA) and polyethylene glycol (PEG) with salt as the particulate. The pore size of the foam structure is controlled by the particulates size and higher interconnectivity is achieved by the co‐continuous blending morphology of the PLA matrix with the water‐soluble PEG. PLA is a fully bio‐based thermoplastic polymer and is derived from renewable resources, such as cornstarch or sugarcanes. PEG is also fully biodegradable polymer produced from ethylene. Fabricated foams were characterized for cellular, acoustic, and mechanical properties. The acoustic performance of the foams was studied by measuring the normal incident absorption coefficient in accordance with the ASTM E1050 standard. The results show open porosity as high as 88% was achieved and the effect of water‐soluble polymer on cellular properties and acoustic and mechanical performance of the foams was studied. As a result of the secondary porous structure formed into cell walls by water soluble polymer, the overall absorption of fabricated PLA foams was increased to above 90% while the average absorption of the foams remained unchanged. In addition, the resulting acoustic foams are benign and environmentally friendly. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39518.     

Preparation of porous poly(D,L‐lactide) and poly(D,L‐lactide‐co‐glycolide) membranes by a phase inversion process and investigation of their morphological changes as cell culture scaffolds

Porous membranes composed of the biodegradable polyesters poly(D,L ‐lactide) (PLA) and poly(D,L ‐lactide‐co‐glycolide) (PLGA) were prepared by a phase inversion process. The molecular weights of the polymers and the concentrations of the polymer solutions affected the pore size and structure of the PLA and PLGA membranes. The molecular weights and morphological changes of the membranes as a function of time were investigated under incubation at 37°C in a humidified 5% CO₂ atmosphere. The pores that formed in the membranes changed dramatically with increasing time under these conditions. From the thermal characterization of the polymers in their dry and wet states, we found that the glass‐transition temperatures of PLA and PLGA affected morphological structure changes in the porous membranes. We also prepared a collagen‐coated membrane to improve the interaction between the cell and the substrate, and we observed that the collagen coating enhanced the attachment and growth of Chinese hamster ovary cells on the substrate. Finally, we found that only PLA was a suitable material to prepare a porous membrane scaffold with the phase inversion process with PLA, and a collagen coating was necessary for cell culture on the membrane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2082–2092, 2004     

Modification and extrusion coating of polylactic acid films

Polyethylene (PE) extrusion coating on paper substrates are the traditional packing material for coffee cups and take‐out food containers. It is difficult to recycle the PE/paper laminates and the thin polymer films remain in landfills after the decomposition of their paper substrates. Disposal of plastic materials is causing serious effects on our environment and wildlife. Demand for compostable or biodegradable plastic packaging products is increasing because of consumer pressure and legislation. Biodegradable polylactic acid (PLA) is regarded as one of the most promising biopolymers with a large market potential, but its applications are limited by poor thermal stability, mechanical properties and processibility. We utilize modified gelatin as additives to improve PLA's performance without compromizing the biomass origin and compostable properties of the material. Extrusion coating, or extrusion casting, of polylactic acid (PLA) films onto paper substrates to form PLA/paper laminates was achieved by modification of the polymer with a plant or animal gelatin. Various paper substrates with thin PLA coatings were prepared using a conventional extrusion coating equipment for the fabrication of take‐out food containers and coffee cups. Melt rheology of PLA and adhesion of the resulting thin film were greatly improved in the presence of a small amount of gelatin in the polymer matrices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42472.     

Porous polyimide films obtained by using lithium chloride as pore‐forming agent

Porous polymer films have been obtained from polyimide based on benzophenonetetracarboxylic dianhydride and 4,4'‐diamino‐3,3'‐dimethyl‐diphenylmethane by incorporating lithium chloride (LiCl) in the poly(amidic acid) precursor and subsequently leaching out the maximum possible LiCl by water Soxhlet extraction for 6 h. The resulting porous polyimide films were characterized with regard to their pore size, thermal stability and dielectric properties. The morphology of the porous polyimide films showed a uniform distribution and various pore sizes depending on the initial quantity of added pore‐forming agent. © 2013 Society of Chemical Industry     

Selective Coating of SnS on the Bio‐Inspired Moth‐Eye Patterned PEDOT:PSS Polymer Films

A new strategy for the selective coating of tin sulfide (SnS) on the surface of moth‐eye patterned (MEP) conducting polymer film is studied by considering the optical properties of the antireflective moth‐eye pattern and flexibility of polymer films. The semiconductor SnS is selectively coated on the surface of MEP microdomes of poly(3,4‐ethylenedioxythiophene) poly(styrene‐sulfonate) (PEDOT:PSS) film. The SnS coated MEP film is obtained by using pore selectively SnS thin layer functionalized polystyrene honeycomb‐patterned porous (HCP) film as a template. Aqueous PEDOT:PSS solution is poured on the SnS functionalized HCP films and detached for the fabrication of SnS coated MEP films. The films show a satisfactory photo‐responsive property under solar stimulated light illumination due to the antireflective MEP structure of PEDOT film and homogenous SnS coating on the surface of the conducting polymer.     

Controlled degradation of porous poly(lactide) stereocomplex films prepared by the selective extraction of co-assembled poly(vinyl alcohol)

Summary Poly(vinyl alcohol) (PVA) layers of different thicknesses were intercalated into stereocomplex films composed of poly(L-lactide) and poly(D-lactide). The immersion of composite films into boiling water selectively extracted the water-soluble PVA components, resulting in porous stereocomplex films. The hydrolytic properties of the porous films under alkaline conditions were then quantitatively analyzed. It was observed that the hydrolytic rates decreased with increasing pore sizes.     

Optimized route for the production of zirconia structures with controlled surface porosity for biomedical applications

Zirconia structures with controlled surface porosity may be used in several biomedical and engineering applications. This work aimed at developing a processing route for the production of zirconia structures with porous surfaces, using the dip coating method and without pore forming additives. Zirconia powders (~ 40?µm diameter) were used in the dip coating suspensions in three different forms: agglomerates (as received), pre-sintered (1150?°C, 1?h) and sintered (1500?°C, 2?h). The addition of fine particles (< 10?µm diameter) to the suspensions, in different contents, were tested to act as binder for the larger particles. Zirconia disk-shape compacts were dipped in the different suspensions and sintered. Pre-sintered powders were found to be the most adequate for producing the porous surface. The optimized binder content was determined as a function of the porous layer strength. A feasible route could be successfully established for the production of zirconia structures with porous surface.     

Heterogeneous latices as binders in porous particle structures

Heterogeneous carboxylated styrene-butadiene (S/Bu) latices were prepared by a two-stage polymerization process, using three seeds of polystyrene with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu-ratio of 1 and a methacrylic acid (MAA) content of either 1 or 10 wt %. It has been found that the morphology of the films made from these latices influenced the modulus in the rubbery region of these films. The heterogeneous latices were used as binders in porous structures based on micron-sized kaolin particles. Such structures are typically employed as paper coatings. Polyester substrates were coated with aqueous suspensions containing the kaolin particles and the heterogeneous latex. The coatings were dried at room temperature, which corresponds to the rubbery region of the latex films. It was found that a higher modulus (which is determined here by the morphology of the latex film) in the rubbery region of the films was associated with coating layers with higher porosity, greater light scattering ability, and higher coating gloss. This is interpreted as being the result of a retarded shrinkage of the coating layers during the drying of these structures due to the increase in modulus of the latex films. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 661–670, 1997     

Formation of porous glass via core/shell-structured poly(methyl methacrylate)/powder glass prepared by ultrasonic irradiation in liquid CO2

The formation of porous glass ceramic via core/shell-structured poly(methyl methacrylate)(PMMA)/powder glass was investigated. Core/shell structures were prepared via ultrasonic irradiation in high-pressure liquid carbon dioxide (CO₂) using PMMA microspheres as the core material and glass powder as the shell material. The mean particles sizes of PMMA template microspheres and glass powder were 9.8 μm and 0.9 μm, respectively. After removal of the PMMA template by calcination in air, porous glass was obtained. The products were characterized by scanning electronic microscopy (SEM) and thermogravimetric-differential thermal analysis (TG-DTA). The average pore diameter of porous glass was 4.3 μm. Compared with porous glass prepared by the other method, the porous glass prepared by ultrasonic irradiation of liquid CO₂ was achieved the narrow pore size distribution (CV = 35%) and the higher porosity (89%). The pores are not isolated and connected each other. Furthermore, the effects of experimental conditions, such as coating method, crosslink density of the template PMMA microspheres, ultrasonic intensity and calcination temperature, on the product morphology were investigated. The higher ultrasound intensity achieved the uniform coating of PMMA templates with powder glass. The calcination temperature and crosslinked density of PMMA template microspheres affect the pore structure.     

聚乳酸⁃羟基乙酸共聚物涂层对聚乳酸3D打印支架的性能影响

通过熔融沉积（FDM）三维（3D）打印技术制备了61.7 %孔隙率和良好连通性的3D多孔聚乳酸（PLA）支架,使用浸涂法对PLA支架表面涂覆浓度分别为2 %、4 %、6 %、8 %的聚乳酸⁃羟基乙酸共聚物（PLGA）涂层,获得了不同浓度涂层的PLA/PLGA复合支架。通过扫描电子显微镜（SEM）、接触角测量仪、万能试验机和细胞计数试剂盒⁃8方法等测试手段,探究了不同浓度PLGA涂层对PLA支架的断面微观形貌、支架表面亲水性、力学强度以及细胞在支架上增殖活性等性能的影响规律。结果表明,与未经包裹的PLA支架相比,包裹PLGA的PLA支架表面接触角显著减小,PLGA的质量分数为6 %时接触角最小为（64.7±1.1） °;接种后经24 h培养PLA/PLGA支架表面细胞活性较纯PLA支架显著增强。     

Fabrication of polylactic acid/polyethylene glycol (PLA/PEG) porous scaffold by supercritical CO2 foaming and particle leaching

PLA/PEG/NaCl blends were melt‐blended followed by gas foaming and particle leaching process to fabricate porous scaffold with high porosity and interconnectivity. A home‐made triple‐screw compounding extruder was used to intensify the mixability and dispersion of NaCl and PEG in the PLA matrix. Supercritical carbon dioxide was used as physical blowing agent for the microcellular foaming process. Sodium chloride (NaCl) was used as the porogen to further improve the porosity of PLA scaffold. This study investigated the effects of PEG and NaCl on the structure and properties of the PLA‐based blend, as well as the porosity, pore size, interconnectivity, and hydrophilicity of porous scaffolds. It was found that the incorporation of PEG and NaCl significantly improved the crystallization rate and reduced viscoelasticity of PLA. Moreover, scaffolds obtained from PLA/PEG/NaCl blends had an interconnected bimodal porous structure with the open‐pore content about 86% and the highest porosity of 80%. And the presence of PEG in PLA/NaCl composite improved the extraction ability of NaCl particles during leaching process, which resulted in a well‐interconnected structure. The biocompatibility of the porous scaffolds fabricated was verified by culturing fibroblast cells for 10 days. POLYM. ENG. SCI., 55:1339–1348, 2015. © 2015 Society of Plastics Engineers     

Hierarchically porous polymeric materials from ternary polymer blends

Hierarchically porous polymers with controllable pore size were generated through a novel polymer blending strategy in an A/B/C–B–C ternary blend system. Polylactide/high-density polyethylene/poly(styrene-ethylene/butylene-styrene) triblock copolymer (PLA/HDPE/SEBS) was used as a model system to demonstrate this technique. During melt blending, the SEBS was driven into the HDPE phase owing to the presence of the PE block in the copolymer. With proper volume fractions of PLA/HDPE/SEBS (e.g., 50/25/25), a bi-modal, dual co-continuous morphology was obtained and hierarchically porous polymeric materials were further generated by selectively removing the PLA and SEBS phases. Annealing and compositional variation were further employed to control the pore size and it is shown that the length scales of the two co-continuous morphologies can be controlled independently.     

Reactive modification and compatibilization of poly(lactide) and poly(butylene adipate‐co‐terephthalate) blends with epoxy functionalized‐poly(lactide) for blown film applications

Biodegradable blown films comprising of poly(lactide) (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) were produced using epoxy functionalized‐poly(lactide) (EF‐PLA) reactive modifiers for rheological enhancement and compatibilization. The epoxy groups on the EF‐PLA modifiers react with PBAT forming an in situ copolymer that localizes at the blend interphase resulting in compatibilization of the polymer blend components. The EF‐PLA modified polymer blends have improved melt strength and the resultant films showed better processability as seen by increased bubbled stability. This allowed for blown films with higher PLA content (70%) compared to the unmodified control films (40%). The static charge build‐up typically experienced with PLA film blowing was decreased with the inclusion of EF‐PLA yielding films with better slip and softness. The compatibilization effect of the EF‐PLA modifiers resulted in significant improvement in mechanical properties. For example, dart test performance was up to four times higher than the control, especially at higher PLA concentrations. Therefore, the rheological enhancement and compatibilization effects of the EF‐PLA reactive modifiers make them ideally suited to create high PLA content films. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43310.     

可降解聚乳酸多孔微球的制备探究

以聚乳酸为壁材,碳酸氢铵为致孔剂,采用双乳液溶剂挥发法,制备出具有孔状的聚乳酸微球,探讨制备条件对聚乳酸微球的影响.结果表明,在内外水相体积比1∶7.5,初乳化搅拌速度1 000 r/min下制得的PLA多孔微球的球形和孔结构较好.     

Poly(d,l-lactide)/poly(methyl methacrylate) interpenetrating polymer networks: Synthesis, characterization, and use as precursors to porous polymeric materials

The use of semi-hydrolyzable oligoester-derivatized interpenetrating polymer networks (IPNs) as nanostructured precursors provides a straightforward and versatile approach toward mesoporous networks. Different poly(d,l-lactide) (PLA)/poly(methyl methacrylate) (PMMA)-based IPNs were synthesized by resorting to the so-called in situ sequential method. The PLA sub-network was first generated from a dihydroxy-telechelic PLA oligomer via an end-linking reaction with Desmodur^® RU as a triisocyanate cross-linker. Subsequently, the methacrylic sub-network was created by free-radical copolymerization of methyl methacrylate (MMA) and a dimethacrylate (either bisphenol A dimethacrylate or diurethane dimethacrylate) with varying compositions (initial MMA/dimethacrylate composition ranging from 99/1 to 90/10 mol%). Both cross-linking processes were monitored by real-time infrared spectroscopy. The microphase separation developed in IPN precursors was investigated by differential scanning calorimetry (DSC). Furthermore, the quantitative hydrolysis of the PLA sub-network, under mild basic conditions, afforded porous methacrylic structures with pore sizes ranging from 10 to 100 nm -at most- thus showing the effective role of cross-linked PLA sub-chains as porogen templates. Pore sizes and pore size distributions were determined by scanning electron microscopy (SEM) and thermoporometry via DSC measurements. The mesoporosity of residual networks could be attributed to the good degree of chain interpenetration associated with both sub-networks in IPN precursors, due to their peculiar interlocking framework.     

静电纺聚乳酸纳米纤维的制备及其孔结构调控

为了调控聚乳酸(PLA)纳米纤维的孔结构,采用静电纺丝技术,以PLA母粒为原料,三氯甲烷(CF)和N,N-二甲基甲酰胺(DMF)按一定比例混合的溶液为溶剂,制备了平均直径在1.37μm的PLA纳米纤维,并对其结构进行表征。结果表明,PLA纳米纤维的平均直径随着纺丝液中CF含量、聚合物浓度、环境湿度的增加而增大;随纺丝电压和灌注速度的增大而呈减小的趋势。同时,环境湿度对纤维表面孔结构有显著影响。随着湿度的增加,纤维表面孔的分布密度增加,且形状由圆形转变为椭圆形。此外,与表面光滑的PLA纳米纤维(2.4 m²/g)相比,所制备的PLA多孔纤维的比表面积提升了10倍(24.0 m²/g)。     

Strength Degradation of Nonrandom Porous Ceramic Structures under Uniaxial Compressive Loading

Nonrandom porous mullite ceramics with controlled pore geometry have been fabricated using a lost mold process, where the molds were fabricated using the fused deposition process from CAD data. The pore geometry of molds was varied to achieve different pore sizes and shapes. These porous ceramic structures were then tested under uniaxial compression to evaluate their strength degradation for different pore volumes created by varying pore sizes and shapes. The finite element method (FEM) has been used to understand the effect of these porosity parameters based on stress concentrations along pore boundaries. Strength degradation of porous ceramics was found to be related to the increase in stress concentration along the pore boundaries in three-dimensional nonrandom porous ceramics.