Surface-modified Polyvinylidene Fluoride Research Articles

Cross-section modified and highly elastic sutures reduce tissue incision and show comparable biocompatibility: in-vitro and in-vivo evaluation of novel thermoplastic urethane surgical threads.

Surgical sutures are indispensable for a vast majority of operative procedures. An ideal suture is characterized by high tissue compliance without cutting into the mended tissue and optimal biocompatibility. Therefore, we assessed these mechanical and biological properties for novel elastic thermoplastic polyurethane (TPU) and cross-sectional modified "snowflake" sutures. Circular and "snowflake"-shaped TPU threads were manufactured and compared to similar surface modified polyvinylidene fluoride (PVDF) sutures. Regular PVDF sutures were used as the control group. Single-axis tensile test with and without gelatinous tissue surrogates were performed to evaluate the suture incision into the specimens. Biocompatibility was evaluated by subcutaneous implantation (n = 18) in rats for 7 and 21 days. Histology and immunohistology was conducted for assessment of the foreign body reaction. Regular and modified TPU threads showed a significant reduction of incision into the tissue surrogates compared to the control. Both TPU sutures and the modified PVDF sutures achieved comparable biocompatibility versus regular PVDF threads. Detailed histology revealed novel tissue integration into the notches of the surface modified sutures, we termed this newly shaped granuloma "intrafilamentous" granuloma. Elastic TPU threads showed a significant reduction of tissue surrogate incision and suture tension loss. Biocompatibility did not significantly differ from standard PVDF. Histology demonstrated tissue ingrowth following the surface modification of the suture referred to as "intrafilamentous" granuloma. Further in vivo studies are required to illuminate the exact potential of the new sutures to optimize intestinal anastomosis.

Effects of Plasma-Modified Polyvinylidenefluoride and Polyethersulfone Ultrafiltration (UF) Membrane Treatments on Quality of Soybean Oil

The effects of unmodified and surface-modified polyvinylidenefluoride (PVDF) and polyethersulfone (PES) ultrafiltration membranes on quality of crude soybean oil and crude oil miscellas were studied. Membranes were modified with hexamethyldisiloxane in radiofrequency plasma polymerization (PlzP) at 60 W (PVDF) or 75 W (PES) glow discharge power for 5 min. Contact angle results indicated an interfacial free energy increase between water and solid surface by 2.1- and 12.7-fold for PVDF and PES, respectively, after PlzP, i.e., both membranes became more hydrophobic. Modified PVDF removed 10% more free fatty acids, 8–11% peroxides, and maintained 2–5% more tocopherols compared to those of unmodified PVDF and modified PES. Oxidation products and color compound removal of modified PVDF from crude oil and miscellas were similar to the commercial bleaching step and better than degumming-neutralization step. Total tocopherol loss during modified PVDF treatment was 5.3% and 5.0–6.8% for crude oil and miscellas, respectively, and these values were far below than any processing steps in commercial refining (10.4–28.4% loss). Practical Applications PlzP coating of monomers on a polymeric-based membrane changes the membrane's chemical and physical properties due to series of sequential reactions such as oxidation, degradation and cross-linking. The predominant reactions were determined mainly with plasma power and plasma treatment time. Thus, if one can adjust the plasma parameters properly, one can create a tailor-made surface in terms of angstroms at the molecular/atomic level. The minimal refining method with plasma-modified PVDF and PES membranes described in the present study was a new practical approach to remove undesirable components from crude soybean oil as well as crude oil-hexane miscellas for meeting commercial refining standards. It simultaneously preserves the more healthy minor components found in oil.

Microfiltration and ultrafiltration as a post-treatment of biogas plant digestates for producing concentrated fertilizers

Biogas plant digestate liquid fractions can be concentrated by microfiltration and ultrafiltration. Two types of microfiltration membranes (polysulphone (PS) and surface-modified polyvinylidene fluoride (PVDF)) were used to process digestate liquid fractions, and to assess their applicability in the recovery of particulate phosphorus, compared to an ultrafiltration membrane (polyethersulphone (PES)). Results show that membrane material, operational conditions, and pore diameter influenced the permeate flux pattern during microfiltration. The PS membranes initially had a higher tendency to foul than PVDF membranes. However, during the filtration process, as fouling built up, the permeate flux behavior of the two membranes became very similar. During the concentration of digestate liquid fractions, the microfiltration PS membrane and the ultrafiltration PES membrane achieved the highest phosphorus rejection (80% w/w), suggesting that there was a correlation between the membrane material and both the fouling trend and phosphorus rejection. A two-step basic-acidic cleaning was unable to recover the initial water flux for the fouled microfiltration membranes. In conclusion, the PS microfiltration membranes might be a good strategy for recovering phosphorus from digestate liquid fractions. Further research leading to adequate cleaning procedures, for microfiltration PS and PVDF membranes treating digestate liquid fractions though, are needed.

Study on the effect of air–gap length on properties and performance of surface modified PVDF hollow fiber membrane contactor for carbon dioxide absorption

Surface modified polyvinylidene fluoride (PVDF) hollow fiber membranes (HFMs) were spun via dry–wet spinning technique at different air–gap lengths (0–20cm). The morphology of prepared membranes was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Membranes were also characterized in terms of gas permeation, overall porosity, collapsing pressure, critical water entry pressure (CEPw) and contact angle. To determine the CO2 absorption flux of HFMs, a gas–liquid membrane contactor system was used. Experimental results of this study revealed that by increasing the air–gap distance from 0 to 20cm, wetting resistance and contact angle of fabricated membranes increased due to enhancement of membrane surface hydrophobicity. The highest helium (He) permeation was achieved for the spun fiber at the air–gap of 10cm. From CO2 absorption experiment it was found that the hollow fiber spun at the air–gap of 10cm had the maximum CO2 absorption flux of 1.41×10−3mol/m2s at the absorbent flow rate of 300ml/min, which was significantly higher than CO2 absorption flux obtained by other researchers. It was also found that both highest He gas permeance and CO2 absorption flux were controlled by the surface porosity of the hollow fiber due to the maximum values obtained. Thus, the choice of an appropriate air–gap distance for fabrication of surface modified membranes was found to be a promising method to improve CO2 removal in membrane contactor systems.

Effect of SMM concentration on morphology and performance of surface modified PVDF hollow fiber membrane contactor for CO2 absorption

Surface modified polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated via a dry–wet phased inversion process. Surface modifying macromolecules (SMMs) (0, 2, 4 and 6wt.%) were used as additives in the spinning dope. During phase inversion SMM migrates to the membrane surface, resulting in different surface morphology and surface chemistry. The surface modified PVDF membranes showed the larger pore size, higher gas permeance, effective surface porosity, contact angle and overall porosity but lower critical water entry pressure compared to the PVDF hollow fiber membrane without SMM. The performance of the surface modified membrane in contactor application for physical CO2 absorption was investigated by the fabricated gas–liquid membrane contactor module, where distilled water was used to dissolve CO2. It was found that the liquid phase resistance was dominant in the absorption experiment. The results show that the surface modified PVDF membrane has a higher performance compared to control PVDF membrane. By increasing SMM concentration in the spinning dope, the CO2 absorption flux increased significantly. With the membrane prepared from 6wt.% of SMM in the spinning dope, a maximum CO2 absorption flux of 5.4×10−3mol/m2s was achieved at 300mlmin−1 of absorbent flow rate, which was almost 650% more than the fabricated membrane without SMM.

A novel surface modified polyvinylidene fluoride hollow fiber membrane contactor for CO2 absorption

A novel surface modified polyvinylidene fluoride (PVDF) hollow fiber membrane was fabricated via a dry–wet phased inversion process. A surface modifying macromolecule (SMM) was used as an additive in the spinning dope. During phase inversion SMM migrates to the membrane surface and functions as both a pore former and surface modifier. The surface modified PVDF membrane showed large pore size, higher effective surface porosity, contact angle and porosity but lower critical water entry pressure compared to the PVDF hollow fiber membrane without SMM. The performance of the surface modified membrane in contactor application for CO2 absorption via distilled water as absorbent was studied. The results show that the surface modified PVDF membrane has higher performance compared to control PVDF membranes. With the membrane prepared from SMM in the spinning dope a maximum CO2 flux of 7.7×10−4 mol/m2 s was achieved at 300 ml/min of absorbent flow rate, which was almost 93% more than the other membrane. In a long-term stability study, CO2 flux was decreased only about 7.7% by using surface modified PVDF membrane during 150 h operation.