Polylactide. III. Fiber preparation by spinning in precipitant vapor

The mechanical properties and morphologies of poly(L-lactide) (PLLA) fibers, prepared by spinning in different vapor precipitants and hot drawing afterward, were studied in relation to fiber in vitro degradability. Petrolether, methanol, and ethanol were employed as precipitants. PLLA was used as-polymerized, i.e., with 10% of residual L-lactide. The tensile strength, structure, and degradability of obtained fibers were mainly governed by the nonsolvent concentration in the vapor phase. Using methanol as the precipitant for the fiber preparation, total tensile strength loss was achieved during 12 wk of in vitro degradation. © 1994 John Wiley & Sons, Inc.     

Resorbable materials of poly(L-lactide). V. Influence of secondary structure on the mechanical properties and hydrolyzability of poly(L-lactide) fibers produced by a dry-spinning method

Fibers of poly(L -lactide) (PLLA) with a loosened fibrillar structure were produced by solution spinning from a good solvent (chloroform) in the presence of various additives (camphor, polyurethanes). No decrease in mechanical properties was observed as compared with PLLA fibers spun from a good solvent only. In vitro degradation studies showed that the rate of degradation of PLLA fibers with the loosened fibrillar structure was increased approaching that found for fibers composed of the homopolymer of glycolide or copolymers of glycolide and L-lactide. Helices on the fiber surface caused by melt fracture during spinning of the fibers leads to higher knot strengths of the hot-drawn PLLA fiber up to 70% of the tensile strength.     

Polylactide. I. Continuous dry spinning–hot drawing preparation of fibers

The mechanical properties and in vitro degradability of gamma-rays sterilized and non-sterlized PLLA fibers prepared by a continuous dry spinning–hot drawing process were studied in relation to the spinning solution composition. Chloroform/cyclohexane mixtures of different volume ratios were used for dissolution either purified or as polymerized (with a residual monomer) PLLA. The fibers obtained had average or poor mechanical properties and a porous structure with a pointed outer skin. No increase of the degradation rate was observed except for the fibers formed from pure chloroform with a residual monomer at a drawing temperature of 110°C. At chloroform/cyclohexane volume ratio of 6:4 the process resulted in nearly hollow fiber formation. © 1994 John Wiley & Sons, Inc.     

PHB/PLLA/PEO共混纤维的晶态结构与拉伸性能研究

采用溶液干纺法制备了聚β-羟基丁酸酯/聚乳酸/聚氧乙烯(PHB/PLLA/PEO)共混纤维,研究了PHB/PLLA/PEO初生纤维的晶态结构、在50℃和110℃下拉伸后共混纤维的力学性能及表面形态。结果表明:PHB与PLLA在PHB/PLLA/PEO共混纤维中的晶型均为α晶型;初生纤维经50℃和110℃拉伸2倍后,纤维的断裂强度均有所增加,断裂伸长率减小,50℃拉伸的纤维断裂强度高于110℃拉伸,其断裂方式均为韧性断裂;w(PEO)为5%,PHB/PLLA质量比为1:1,50℃拉伸2倍的PHB/PLLA/PEO共混纤维断裂强度为0.471 cN/dtex,断裂伸长率为34.05%     

Stereocomplex formation between enantiomeric poly(lactic acid). VIII. Complex fibers spun from mixed solution of poly(D-lactic acid) and poly(L-lactic acid)

To obtain poly(lactic acid) (PLA) complex fibers, spinning was performed by wet and dry methods from 5–10 g/dL chloroform solutions of poly(D-lactic acid) (PDLA) and poly(L-lactic), both with a viscosity-average molecular weight of 3 × 10⁵. The dope was extruded from a monohole nozzle into coagulation baths from ethanol and chloroform for wet spinning and into a drying column kept at 60°C for dry spinning. Scanning electron microscopic observation of the as-spun fibers showed that the surface of the wet-spun fiber had large basins with diameters of 50–100 μm and many pores with diameters from sub μm to 10 μm, whereas the surface of dry-spun fiber had a microporous structure with the pore diameter of 1–3 μm. The tensile strength of the wet-spun complex fiber was very low and could not be drawn at high temperatures, in contrast to the dry-spun fiber. The tensile strength of dry-spun complex fiber increased upon hot drawing and showed the tensile strength of 94 kg/mm² by drawing at 160°C to the draw ratio of 13. Differential scanning calorimetry revealed that the complex fibers contained both the stereocomplex crystallites (racemic crystallites) and the crystallites of the single polymers, PDLA and PLLA, regardless of the spinning methods. The ratio of the racemic crystallites to the single-polymer crystallites increased with the draw ratio of the complex fiber. © 1994 John Wiley & Sons, Inc.     

High-strength poly(L-lactide) fibers by a dry-spinning/hot-drawing process. II. Influence of the extrusion speed and winding speed on the dry-spinning process

This paper is concerned with the influences of the extrusion speed and the winding speed during dry spinning of 4 wt % solutions of poly(L -lactide) (PLLA) in mixtures of chloroform and toluene, on the ultimate fiber tenacities after hot drawing. It was found that high-strength PLLA fibers (1.5 GPa) can be produced at high spinning rates (> 180 m/min) if rupturing of the entanglement network and oriented crystallization during spinning is suppressed. This could be accomplished by avoiding spinline stretching and applying low elongational deformation rates in the spinneret during spinning.     

Melt electrospinning from poly(L‐lactide) rods coated with poly(ethylene‐co‐vinyl alcohol)

Rodlike poly(L ‐lactide) (PLLA) samples coated with poly(ethylene‐co‐vinyl alcohol) (EVOH) were made. Fibers were produced from these rodlike samples by using a melt electrospinning system equipped with a laser irradiating device, and the effects of EVOH content and the processing parameters of the melt electrospinning on fiber diameters were investigated. We also studied the fiber formation mechanism from the rods during the laser melt electrospinning process. The following conclusions were reached: (i) coating of EVOH on PLLA rods has a remarkable effect on decreasing fiber diameter from 3 μm to around 1 μm; (ii) increases in the electric field strength and temperature of spinning space decrease the average diameter of fibers produced from pure PLLA rods, and longer collector distance leads to lager PLLA fiber diameter; and (iii) the migration of PLLA component from the core to the surface of electrospun fibers takes place during the fiber formation process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Wet-spinning assembly of continuous and macroscopic graphene oxide/polyacrylonitrile reinforced composite fibers with enhanced mechanical properties and thermal stability

Polyacrylonitrile (PAN) composite microfibers with different contents of graphene oxide (GO) were fabricated via wet-spinning route in this work. Based on nonsolvent-induced phase separation theory, N,N-dimethyl formamide/water mixture system was employed as coagulation bath, nonsolvent (water) diffused into PAN spinning solution and led to a quick PAN fiber solidification. Nematic liquid crystal state of GO dispersions and GO/PAN spinning solutions were determined via polarized optical microscopy images, and the morphology and structure of the composite fibers were characterized via scanning electron microscope, Transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. 1 wt % GO/PAN composite fibers exhibited outstanding mechanical properties, 40% enhancement in tensile strength and 34% enhancement in Young's modulus compared with pure PAN fiber. The results of dynamic mechanical analysis indicated that the composite fiber with 1 wt % GO performed the best thermal mechanical property with 5.5 GPa and 0.139 in storage modulus and loss tangent, respectively. In addition, thermogravimetric analysis showed that thermal stability of the composite fibers enhanced with the increasing GO contents. GO/PAN composite fibers can be as the candidate of carbon fiber precursor, high performance fibers, and textiles applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46950.     

Processing,structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry‐jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent‐free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from ?50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as‐spun fiber cross‐sectional shape, as well as the as‐spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as‐spun fibers were then drawn to investigate the relationship between as‐spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as‐spun fibers with an irregular cross‐sectional shape produced using a ?50°C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross‐section. POLYM. ENG. SCI., 55:2603–2614, 2015. © 2015 Society of Plastics Engineers     

聚乳酸/聚乙醇酸复合纤维的性能探讨

对聚乳酸(PLLA)、聚乙醇酸(PGA)以复合比为85/15,70/30分别进行复合纺丝,制得两种皮芯复 合纤维,并对纤维的热性能、力学性能和结晶性能进行探讨。结果表明:PGA和PLLA在熔融纺丝时,没有发 生反应。纤维的强度随拉伸倍数的增加而增大,结晶度和取向度也都得到提高。复合纤维皮芯结合紧密,没 有裂隙和孔洞。     

Melt spinning of poly(L‐lactic acid) and its biodegradability

The melt spinning and melt drawing of poly(L ‐lactic acid) (PLLA) were carried out with a melt‐spinning machine, and the mechanical properties, structure, and biodegradability of PLLA fiber were investigated. PLLA fiber with a tensile strength of 0.81 GPa was successfully obtained through two steps of drawing at a draw ratio of 18 in hot water. This fiber had enough tensile strength for common engineering use. The fiber could be degraded under controlled composting conditions at 70°C for 1 week. In scanning electron microscopy observations of the fiber, a regular pattern of cracks running along the vertical direction to the fiber axis was clearly observed. This suggested that the PLLA fiber built up a highly ordered structure arranged along the direction of the fiber axis. After the fiber was left to lie in the ground for 1 year, however, the surface of the fiber was still smooth, and the tensile strength did not decrease much. This PLLA fiber could not be hydrolyzed after 1 month of steeping in a buffer solution at 37°C, but it was rapidly hydrolyzed at more than 60°C. It was suggested that the degradation (hydrolysis) rate of PLLA depended on the glass‐transition temperature. Upon hydrolysis at 80°C for 48 h, a regular crack along the vertical direction to the fiber axis was found that was very similar to that observed in degradation under composting conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2118–2124, 2005     

Process‐induced monomer on a medical‐grade polymer and its effect on short‐term hydrolytic degradation

While melt‐spinning biodegradable poly‐(L /D )LA 96/4 lactides into fibers, we intentionally induced monomer into the material by thermal degradation. Elevated temperatures and variable residence times were used during processing. By increasing the residence time, the molecular weight decreased, and the amount of monomer increased exponentially. The studied processing parameters induced from 0.17 to 1.24% of monomer into PLA fibers. In short‐term (9‐week) in vitro studies, the rate of degradation was significantly faster for fibers with higher amounts of monomer. After 9 weeks in vitro, the 0.17% monomer fiber lost 3% of its strength, whereas the 1.24% monomer fiber lost 65%. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Bio‐composites for structural applications: Poly‐l‐lactide reinforced with long sisal fiber bundles

Fully bio‐based and biodegradable composites were compression molded from unidirectionally aligned sisal fiber bundles and a polylactide polymer matrix (PLLA). Caustic soda treatment was employed to modify the strength of sisal fibers and to improve fiber to matrix adhesion. Mechanical properties of PLLA/sisal fiber composites improved with caustic soda treatment: the mean flexural strength and modulus increased from 279 MPa and 19.4 GPa respectively to 286 MPa and 22 GPa at a fiber volume fraction of V_f = 0.6. The glass transition temperature decreased with increasing fiber content in composites reinforced with untreated sisal fibers due to interfacial friction. The damping at the caustic soda‐treated fibers‐PLLA interface was reduced due to the presence of transcrystalline morphology at the fiber to matrix interface. It was demonstrated that high strength, high modulus sisal‐PLLA composites can be produced with effective stress transfer at well‐bonded fiber to matrix interfaces. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40999.     

In vitro degradation and biocompatibility of poly(l-lactic acid)/chitosan fiber composites

In this study, poly(l-lactic acid) (PLLA) fibers were prepared by the dry-wet-spinning method, while chitosan (CHS) fibers were prepared via the wet-spinning method. The two fibers were blend spun and then fabricated into PLLA/CHS fabrics. In vitro degradation experiments of the fabrics were carried out in a phosphate-buffered solution at 37 °C with a pH of 7.4. Changes in molecular parameters (molecular weights and molecular weight distributions), phase structures (crystallinities), morphologies (fiber surface topologies) of the PLLA fibers, and their macroscopic properties (the fabric weight losses and mechanical strengths) were monitored with degradation times. These results were compared with control samples with no degradation. The hydrolysis mechanism of PLLA/CHS fabrics was analyzed. It was found that the degradation rate of dry-wet-spun PLLA fibers was higher than those of the melt-spun or dry-spun ones. Furthermore, the compatibility between PLLA/CHS fabrics and osteoblast under the in vitro degradation was investigated for the potential application of using the PLLA/CHS fabrics as supporting materials for chest walls and bones. Cell strain hFOB1.19 human SV40-transfected osteoblast and PLLA/CHS mixed fabrics were incubated. The cell morphology at early stages of cultivation was also studied. Excellent adhesion between osteoblast and PLLA/CHS fabrics was observed, indicating good biocompatibility of the fabrics with osteoblast.     

Resorbable materials of poly(L-lactide). II. Fibers spun from solutions of poly(L-lactide) in good solvents

Fibers of poly(L -lactide) (PLLA) with a tensile strength up to 1.2 GPa and Young's modulus in the range of 12–15 GPA were obtained by a hot drawing of fibers spun from solution of PLLA in good solvents such as dichloromethane and trichloromethane. The tensile strength of fibers was strongly dependent on the molecular weight of PLLA and on polymer concentrations in the spinning solution. Changing of the polymer concentration in the spinning solution gives rise to formation of fibers with different shape and porosity. Fibers spun from 10–20% solutions at room temperature exhibit a regular structurization, due to the melt fracture. These fibers had knot strengths up to 0.6 GPa, whereas fibers with a smooth surface spun from more dilute solutions had weaker square knots up to 0.3 GPa.     

Ripening time and fiber formation of chitosan spinning dope

A study was carried out on the wet spinning of chitosan fibers using 2% acetic acid as a solvent, 10% aqueous sodium hydroxide as a nonsolvent, and 4% chitosan solution as a polymer concentration. In this study, we investigated the effect of the ripening time of the spinning dope on the ability of fiber formation (i‐value), structure, thermal, and mechanical properties (such as fineness, tenacity, elongation, work of rupture, etc.) of chitosan fibers. Based on the results, it can be seen that the ripening time of spinning dope (in days), with the same polymer concentration of spinning dope, changes from 1 to 8, and the i‐value of the spinning dope increased with an increasing of the ripening time. At the ripening time of 8 days, tensile strength, elongation, and work of rupture showed minimum value attributed to the excessive degradation of the chitosan polymer chains left from the mixing operation that took place at the same time as the ripening time of the spinning dope, which means that the optimum ripening time of the spinning dope is 1 to 7 days. However, the thermal decomposition temperature and the onset of the exothermic temperature of thermal properties decreased with an increased ripening time. On the other hand, tenacity, elongation, and toughness decreased with increasing ripening time, and these qualities radically decreased with an increasing ripening time of more than a week. This indicates that the dispersion of aggregates and the degradation of chitosan polymer chains left from the mixing operation occurred at the same time during the ripening time of the spinning dope. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2870–2877, 2003     

Enzymatic Degradation of Biodegradable Polyester Composites of Poly(L‐lactic acid) and Poly(ε‐caprolactone)

Summary: Two different types of biodegradable polyester composites, PLLA fiber‐reinforced PCL and PCL/PLLA blend films were prepared at PCL/PLLA ratio of 88/12 (w/w), together with pure PCL and PLLA films. Their enzymatic degradation was investigated by the use of Rhizopus arrhizus lipase and proteinase K as degradation enzymes for PCL and PLLA chains, respectively. In the FRP film, the presence of PLLA fibers accelerated the lipase‐catalyzed enzymatic degradation of PCL matrix compared with that in the pure PCL film, whereas in the blend film, the presence of PLLA chains dissolved in the continuous PCL‐rich domain retarded the lipase‐catalyzed enzymatic degradation of PCL chains. In contrast, in the FRP film, the proteinase K‐catalyzed enzymatic degradation of PLLA fibers was disturbed compared with that of the pure PLLA film, whereas in the blend film, the proteinase K‐catalyzed enzymatic degradation rate of particulate PLLA‐rich domains was higher than that of pure PLLA film. The reasons for aforementioned enhanced and disturbed enzymatic degradation are discussed.

Normalized PCL weight loss of pure PCL, FRP, and blend films as a function of Rhizopus arrhizus lipase‐catalyzed enzymatic degradation time.     

静电纺丝法纺制聚乳酸纳米纤维无纺毡

采用静电纺丝法制备了生物降解聚乳酸(PLLA)纳米纤维无纺毡。分析了纺丝液浓度、电压、接收距离、挤出速度等因素对纤维形态的影响。结果表明:纺丝液的浓度和挤出速度对纤维直径的影响较为明显,溶液挤出速度增大,所得纤维微孔含量及尺寸也增大;适当的电压和接收距离有利于收集无液滴纤维;随着纤维直径的减小,无纺毡的孔径呈减小趋势。在PLLA质量分数为5．7％、挤出速度0．8 mL／h、接受距离 15．5 cm、电压8 kV的静电纺丝条件下,可制备纤维直径为200-400 nm的PLLA纳米纤维无纺毡。     

Effect of interface and confinement size on the crystallization behavior of PLLA confined in coaxial electrospun fibers

Poly(l ‐lactide)/polyacrylonitrile (PLLA/PAN) core‐sheath composite fibers were fabricated by coaxial electrospinning. The crystallization behavior of PLLA within the coaxial electrospun fibers was studied by differential scanning calorimetry (DSC). The PLLA/PAN coaxial electrospun fiber with a PLLA diameter of ～32 nm (C1) exhibits a crystallization temperature (T_c) of 22.5 °C higher but a cold‐crystallization temperature (T_cc) of 10 °C lower than bulk PLLA. The crystallinity of C1 fiber is also higher than bulk PLLA. In both isothermal melt‐ and cold‐crystallization, PLLA in C1 fiber crystallizes faster than the bulk PLLA, as revealed by the smaller half crystallization times (t_1/2). The enhanced crystallizability of PLLA in the C1 fiber may be attributed to the increased nuclei number and crystal growth rate induced by the PAN surface, i.e., surface‐induction effect. However, PLLA also suffers a nano‐confinement effect exerted by PAN sheath in the coaxial electrospun fiber, which can suppress PLLA crystallization. When the diameter of PLLA is too small (< 32 nm), the nano‐confinement effect may prevail over the surface‐induction effect, leading to a slower crystallization rate and smaller crystallinity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45980.     

Incorporation of salicylates into poly(l-lactide)

Summary Recent studies have indicated that complications like swelling and inflammation of the surrounding tissue may occur in the late stage of thein vivo degradation of semi-crystalline PLLA bone fixation devices. Incorporation of an anti-inflammatory drug, like a salicylate, in the poly(L-lactide) chain might be a route to prevent these complications. In this study, it has been shown that it is possible to copolymerize L-lactide with di- and trisalicylide and to use salicylic acid as an initiator for the L-lactide polymerization or the L-lactide/-caprolactone copolymerization. Furthermore, PLLA was blended with poly(salicylic acid) and Zn(salicylate)2 was synthesized and turned out to be a catalyst for the ring opening polymerization of L-lactide. The binary poly(L-lactide)/o-acetyl salicylic acid system has an eutectic composition for 52 % w/w of poly(L-lactide) in the mixture. Its eutectic melting temperature is 119 °C.