Preparation of Cationic CMP and Softwood Long Fibers as Strength-Enhancing Additive to CMP Pulp
Compared to chemical pulp, mechanical and chemi-mechanical pulps (CMP) are limited in regards to the manufacturing of high quality paper. Chemical additives are an effective way to enhance the properties of paper; however, the effectiveness depends on the additive type and dosage. The utilization of cationized natural polymers has been shown to offer a promising solution. In this study, softwood long fiber (SLF) and CMP were cationized by 3-chloro-2-hydroxypropyl-trimethylammonium-chloride (CHPTAC), and the effects of cationization on the properties of CMP pulp were studied. Cationization was characterized by FTIR and the nitrogen content, and its effect on the CMP properties was evaluated through mechanical tests and fines retention. Cationization at low and moderate levels and in higher mixing rates improved the mechanical properties of CMP. Compared to cationized CMP, the addition of cationized SLF (CLF) improved the strength and fines retention properties. The CLF application to CMP at a CHPTAC dosage of 5% increased the tensile, burst, and tear strengths by 66.4%, 100%, and 3.6%, respectively. The cationized SLF increased the fines retention by 12.7%.
Treatment of Fractionated Fibers with Various Cationic-Modified Poly(vinyl alcohols) and Its Impact on Paper Properties
In this work, the effects of various high molecular weight cationic poly(vinyl alcohols), CPVAs, on the fiber morphology and the properties of papers made from fractionated refined fibers were investigated. At first, bleached sulfite fibers were refined under various revolutions and then refined fibers were fractionated under various time intervals to obtain refined fibers with a similar fiber length and fines content. Then, 20 mg/g CPVAs with various charge densities was adsorbed on the fractionated refined fibers prior to making hand sheets. The results showed that the lower the charge density of CPVA, the higher the effectiveness of CPVA in improving the paper strength at any refining revolution. The reasons for such a phenomenon were perhaps the different configurations of CPVAs on the surface of the fibers and the different adhesion/repulsion forces developed between CPVA-modified fibers in hand sheets. Also, by reducing the freeness of the fractionated fibers (increasing the refining revolutions), t...
Diversity of Electrospinning Approach for Vascular Implants: Multilayered Tubular Scaffolds
Abstract The biomimetics of biological structures found in nature remains one of the most promising approaches to engineer functional tissues from natural or synthetic biocompatible materials for the replacement of damaged or injured parts of the human body. Recently, medical therapeutic regimes have advanced into a new era, overcoming the known mechanical and biological variances that occur when using autologous or synthetic grafts. Basically, the core concept of tissue biofabrication, commonly referred to as tissue engineering, is to find out the favorable cellular microenvironments to grow a living tissue prior to clinical uses. In fact, the ability of stem cells to regenerate is controlled via signaling pathways (growth factors) and supporting materials (scaffolds) that guide the cellular activities. After the first successful experiments to fabricate polymer fibers from their solutions, Cooley proposed the use of an electric field a century ago (Cooley (US 692:631, 1902 ). The electrospinning technique has been continually developed as a fruitful polymer processing technique to draw ultrafine nonwoven fibers. Electrospun polymer fibers have been used for a wide range of technical and biotechnical applications such as filtration, organic solar cells, tissue engineering, and drug releasing implants. In this regard, this review begins with an overview about the various spinning approaches for the fabrication of polymer fibers as well as the basic principles of electrospinning process. In addition, this review will highlight vascular bypass surgery and, in particular, the needs for vascular tissue engineering. Finally, the review includes some of the latest attempts to improve the mechanical and biological properties of electrospun polymeric fibers and summarizes the challenges and prospects for the future. Lay Summary However, vascular defects are treated successfully via bypass surgical bypass grafting using autologous or synthetic vessels. The small-diameter vessels (less than 6) are often associated with high failure rate. This review reports some of the recent features that should be highlighted to fabricate an ideal graft for small-diameter vascular grafts. The review introduces multilayered conduits as an alternative approach to overcome the known mechanical and biological mismatches of single layered vascular grafts of electrospun polymers.