Xin Min Hao

Weak bonds usually make macromolecules stronger; therefore, they are often used to enhance the mechanical strength of polymers. Not enough studies have been reported on the use of weak bonds in flame retardants. A water-soluble polyelectrolyte complex composed of polyethyleneimine (PEI), sodium tripolyphosphate (STPP) and melamine (MEL) was designed and utilized to treat bio-based polyamide 56 (PA56) by a simple three-step process. It was found that weak bonds cross-linked the three compounds to a 3D network structure with MEL on the surface of the coating under mild conditions. The thermal stability and flame retardancy of PA56 fabrics were improved by the controlled coating without losing their mechanical properties. After washing 50 times, PA56 still kept good flame retardancy. The cross-linking network structure of the flame retardant enhanced both the thermal stability and durability of the fabric. STPP acted as a catalyst for the breakage of the PA56 molecular chain, PEI facilitated the char formation and MEL released non-combustible gases. The synergistic effect of all compounds was exploited by using weak bonds. This simple method of developing structures with 3D cross-linking using weak bonds provides a new strategy for the preparation of low-cost and environmentally friendly flame retardants.

In this study, CNFs were provided by an efficient, unmodified, and clean biological method with enzymes and a small amount of alkali, compared to the CNCs with the chemical method involving a strong acid. To provide an accurate targeted selection for future applications, we made the following comparison by analyzing the differences in the preparation method, performance, and application performance of the two nanocelluloses. The result of this study indicated that CNFs and CNCs exhibited a crystallinity index of 58.2 and 83.5%, respectively. CNFs had a mean length (L) of 192.3 nm and a diameter (D) of 1.9 nm, and the average L and D of CNCs reached 123.6 nm and 3.7 nm, respectively. The solution viscosity of CNFs and CNCs reached 7.46 Pa s and 1.91 Pa s, respectively. CNFs and CNCs exhibited zeta potential values of −88.26 mV and −26.40 mV, respectively. The electrospun composite film of PLA–CNFs and PLA–CNCs achieved water contact angles of 138.7 and 34.5°, and the water–oil contact angle reached 24.7 and 30.5°, respectively. The breaking strength of PLA–CNFs and PLA–CNCs reached 96.07 cN and 163.23 cN, and the break elongation followed an order of PLA–CNCs (32.16%) < PLA–CNFs (34.70%). In brief, CNFs can make the composite membrane hydrophobic and with superior extension, and CNCs can make the composite membrane hydrophilic and enhance its strength. Both the composite films conformed to the non-toxic standard, and the PLA–CNFs film more significantly contributed to the cell growth, which is expected to serve as a medical material.

A new kind of bio-based polyamide 5,6 (PA56) fiber has been synthesized from adipic acid and 1,5-pentanediamine. In this report, the characterization, antistatic treatment, mechanical properties, moisture absorption, mass-specific electrical resistance, and static electricity of the PA56 staple fibers were investigated. The spinnability of the PA56 yarns was studied. The results showed that the breaking strength of the PA56 fibers was 3.55 cN·dtex⁻¹, the breaking elongation was 61.60% and the initial modulus was 49.32 cN·dtex⁻¹. The PA56 staple fibers had an excellent moisture absorption of 4.68% and the easy release of water from the fibers. The release of water absorbed on the staple fibers made the carding processing of the PA56 fibers difficult due to electrostatic aggregation. Thus, an antistatic treatment of the PA56 staple fibers was carried out. Compared with the untreated fibers, the treated fibers exhibited a spectacular improvement in conductivity which led to their high efficiency of carding and good spinnability. The potential of the PA56 staple fibers carding web decreased from +21.2 to +0.04 kv when treated. The mass-specific electrical resistance of the treated PA56 staple fibers decreased from more than 10⁴ MΩ·g·cm⁻² to 290 MΩ·g·cm⁻² both at a relative humidity (RH) of 35%, and from 1500 to 9.5 MΩ·g·cm⁻² both at a 65% RH. The Ring yarn and Siro-spun yarn were successful produced by their spinning systems. The measurement results of the yarns demonstrated that the Siro-spun yarn had better properties than the Ring yarn, such as tensile strength, unevenness (CV%), hairiness index (H) and abrasion resistance.

Bio‐based polyamide 56 (PA56) fibers with the circular and trefoil cross‐sections were prepared by high‐speed spinning process. The pre‐oriented yarns (POY) and draw‐textured yarns (DTY) of PA56 were studied. The results showed that γ phase crystal dominated in POY with relative high degrees in the crystallinity and crystal orientation. In DTY, the drawing effect made the crystal transform from γ to α phase with the properties of the enhanced thickness of the crystal plate and the more order arranged molecules, that was the long period in these fibers was obviously increased to 7–8 nm. γ to α phase transition was much easy for PA56 fibers with circular cross‐section during drawing. PA56 fibers had excellent moisture absorption and release performances. They were easy to be dyed and had a good color fastness.