Dual roles of sodium polyacrylate in alginate fiber wet-spinning: Modify the solution rheology and strengthen the fiber.

Limitations to the scaling of sodium alginate (SA) fibers by wet spinning and for commercial applications are the high spinning dope viscosity and low fiber mechanical performance. In this study, the viscosities of SA spinning dopes dramatically reduced to an order of magnitude lower while the maximum spin draw ratio increased from 1 to 6 as sodium polyacrylate (PAAS) loading increased up to 20 %. However, distinct to a simple plasticizing effect, adding appropriate amount of PAAS strengthens the mechanical properties of fully drawn fibers, through the formation of new physical crosslinks with SA. Fibers having the tenacity of ∼0.6 cN/dtex, modulus of ∼37 cN/dtex, strain at break of ∼7 % and toughness of ∼4 J/g were achieved with 15 % PAAS loading. Therefore, the PAAS addition has dual-effects in SA fiber wet spinning: to modify the rheology of the SA spinning solution and to strengthen the wet-spun SA fibers for textile applications.

Using Sodium Polyacrylate to Gel-Spin Lignin/Poly(Vinyl Alcohol) Fiber at High Lignin Content.

Lignin is the world's most naturally abundant aromatic polymer, which makes it a sustainable raw material for engineered polymers and fiber manufacturing. Dry-jet gel-spinning was used to fabricate poly(vinyl alcohol) (PVA) fibers having 30% or more of the lignin biopolymer. To achieve this goal, 0.45 wt.% of aqueous sodium polyacrylate (SPA, at 0.55 wt.% solids) was added to spinning dopes of PVA dissolved in dimethylsulfoxide (DMSO). SPA served to enable the spinning of fibers having high lignin content (i.e., above 30%) while eliminating the aging of as-spun gel fiber prior to elevated temperature drawing. SPA impedes the migration of acetone soluble lignin from the skin of as-spun gel fibers, because SPA is insoluble in acetone, which is also a nonsolvent coagulant for PVA. PVA fibers having 30% lignin exhibited the highest tenacity of 1.3 cN/dtex (centinewton/decitex) and specific modulus 35.7 cN/dtex. The drawn fiber of 70% lignin to PVA, showed tenacity and specific modulus values of 0.94 cN/dtex and 35.3 cN/dtex, respectively. Fourier Transform Infrared (FTIR) spectroscopy showed evidence of hydrogen bonding between lignin and PVA among the drawn fibers. The modification of PVA/lignin dopes with SPA, therefore, allowed for the fabrication of gel-spun biobased fibers without the previously required step of gel aging.

The effect of wet spinning conditions on the structure and properties of poly-4-hydroxybutyrate fibers.

Polyhydroxyalkanoates (PHAs), also known as bacterial polyesters, are considered novel polymers for fabricating biomedical products, such as sutures and hernia meshes, because of their biocompatibility and slow biodegradability. Poly-4-hydroxybutyrate (P4HB) is a commonly used PHA that was explored in this study as an absorbable biomaterial for several medical applications, including controlled drug delivery. Currently, P4HB is melt spun and drawn into filaments at high processing temperatures (~200°C), precluding the incorporation of thermally sensitive drugs within the polymer during melt spinning. Post-spinning drug incorporation can potentially cause nonuniform drug absorption that leads to an uneven release profile. This raises the need for a low temperature spinning process for these polymers. Until now, there has been no defined procedure to produce P4HB fibers through a low temperature solution spinning process. This study focuses on determining suitable wet spinning conditions to form continuous P4HB fibers. After several preliminary tests, it was found that a chloroform-based spin dope with 10-15% polymer concentration facilitated the extrusion of continuous stretchable fibers into a coagulation bath containing reagent alcohol. Subsequently, several P4HB fibers were spun with various spin dope concentrations, coagulation bath temperatures, and spin draw ratios to assess their effect on fiber structure and properties.

Flexible Cyclic-Poly(phthalaldehyde)/Poly(ε-caprolactone) Blend Fibers with Fast Daylight-Triggered Transience.

Cyclic-poly(phthalaldehyde) (cPPHA) exhibits photo-triggerable depolymerization on-demand for applications like the photolithography of microfabricated electronics. However, cPPHA is inherently brittle and thermally sensitive; both of these properties limit its usefulness as an engineering plastic. Prior to this report, small molecule plasticizers are added to cPPHA-based films to make the polymer more flexible. But plasticizers can eventually leach out of cPPHA, then leaving it increasingly more brittle throughout product lifetime. In this research, a new approach to fabricating flexible cPPHA blends for use as spun fibers is achieved through the incorporation of poly (ε-caprolactone) (PCL) by a modified wet spinning method. Among blend compositions, the 50/50 cPPHA/PCL fiber shows fast transience (<50 s) in response to daylight while retaining the flexibility of PCL and mechanical properties of an elastomer (i.e., tensile strength of ≈8 MPa, Young's modulus of ≈118 MPa, and elongation at break of ≈190%). Embedding 2 wt% gold nanoparticles to cPPHA can further improve the transience rate of fibers comprising less than 50% cPPHA. These flexible, daylight-triggerable cPPHA/PCL fibers can be applied to an extensive range of applications, such as wearable electronics, intelligent textiles, and zero waste packaging for which modest mechanical performance and fast transience are desired.

Glucaric acid additives for the antiplasticization of fibers wet spun from cellulose acetate/acetic acid/water.

Cellulose acetate (CA) receives notable attention as an environmentally friendly, biodegradable polymer from renewable, low-cost resources. CA polymers are believed to have a critical role in shaping a greener and more circular textile economy. However, the mechanical properties of CA fibers are among the lowest in terms of its tensile strength, poor wet strength, and low flexural strength. This study investigates the effect of biobased additives for antiplasticizing the mechanical performance and structure of CA fibers. At up to 5 % of CA, glucaric acid (GA) and its monoammonium salt were added to CA fibers. With 1.5 % GA additive, tensile modulus improved by 155%, tensile strength by 55 %, and CA flexibility according to knot to straight fiber tenacity ratios improved by 107 % when compared to neat CA fibers. Based on the results, green small molecule antiplasticizers do exist, but their performance improvements are observed at low percentages of loading.

Thermal properties and surface chemistry of cotton varieties mineralized with calcium carbonate polymorphs by cyclic dipping.

In this study, hydroentangled cotton nonwovens were identified as effective hosts for mineralization of calcium carbonate (CaCO3) polymorphs to modify and improve their properties. All cotton varieties studied, including raw white cotton, scoured white cotton, and raw brown cotton, readily crystallized CaCO3 via a simple cyclic dipping process. A combination of analyses agreed that the surface chemistry of cotton fibers influenced the formation of different CaCO3 polymorphs. Scoured white cotton that consisted of almost pure cellulose predominantly produced the most stable calcite, whereas raw white and raw brown cottons that contain proteins facilitated the production of partial metastable vaterite. The morphology of calcite was better defined on the scoured cotton. The mineralization altered the hydrophobic surface of raw cottons to be hydrophilic, i.e., two-fold increase in moisture regain and decrease in water contact angle from 130 to 0 degrees. The mineralized cottons also exhibited improved thermal resistance, i.e., slower thermal decomposition with decreased activation energies and reduction in heat release capacity by up to 40%.

Role of single-walled carbon nanotubes on ester hydrolysis and topography of electrospun bovine serum albumin/poly(vinyl alcohol) membranes.

Electrospun membranes were studied for the chemical deactivation of threat agents by means of enzymatic proteins. Protein loading and the surface chemistry of hybrid nanofibers influenced the efficacy by which embedded enzymes could digest the substrate of interest. Bovine serum albumin (BSA), selected as a model protein, was electrospun into biologically active fibers of poly(vinyl alcohol), PVA. Single-walled carbon nanotubes (SWNTs) were blended within these mixtures to promote protein assembly during the process of electrospinning and subsequently the ester hydrolysis of the substrates. The SWNT incorporation was shown to influence the topography of PVA/BSA nanofibers and enzymatic activity against paraoxon, a simulant for organophosphate agents and a phosphorus analogue of p-nitrophenyl acetate (PNA). The esterase activity of BSA against PNA was uncompromised upon its inclusion within nanofibrous membranes because similar amounts of PNA were hydrolyzed by BSA in solution and the electrospun BSA. However, the availability of BSA along the fiber surface was shown to affect the ester hydrolysis of paraoxon. Atomic force microscopy images of nanofibers implicated the surface migration of BSA during the electrospinning of SWNT filled dispersions, especially as greater weight fractions of protein were added to the spinning mixtures. In turn, the PVA/SWNT/BSA nanofibers outperformed the nanotube free PVA/BSA membranes in terms of paraoxon digestion. The results support the development of electrospun polymer nanofiber platforms, modulated by SWNTs for enzyme catalytic applications relevant to soldier protective ensembles.