左旋聚乳酸-聚己内酯-醋酸纤维素三维微-纳米复合纤维多孔支架材料的制备与生物矿化活性

赵瑨云; 刘瑞来; 胡家朋; 穆寄林; 付兴平

doi:10.13801/j.cnki.fhclxb.20210906.007

左旋聚乳酸-聚己内酯-醋酸纤维素三维微-纳米复合纤维多孔支架材料的制备与生物矿化活性

赵瑨云^1,,
刘瑞来^{1, 2},
胡家朋^1, ,,
穆寄林¹,
付兴平¹

1.
武夷学院　生态与资源工程学院，武夷山 354300
2.
福建师范大学　化学与材料学院，福州 350007

基金项目: 福建省自然科学基金(2019J01829；2019J01830；2020J01412；2020J01414)；南平市基金(2019J06)

详细信息

通讯作者:
胡家朋，博士，教授，硕士生导师，研究方向为功能高分子材料　E-mail: 22402414@qq.com

中图分类号: TB323.4
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出版历程
- 收稿日期: 2021-06-22
- 修回日期: 2021-08-10
- 录用日期: 2021-08-13
- 网络出版日期: 2021-09-06
- 刊出日期: 2022-05-31

Fabrication of polycaprolactone-cellulose acetate-poly(L-lactic acid) three-dimensional micro-nanofibrous porous scaffold composites and its bio-mineralization activity

1.
College of Ecological and Resources Engineering, Wuyi University, Wuyishan 354300, China
2.
College of Chemistry and Materials Science, Fujian Normal University, Fuzhou 350007, China

摘要

摘要: 3D纳米纤维多孔支架作为骨组织工程支架材料具有很好的发展前景。在无其它任何添加剂条件下，通过低温相分离方法制备了左旋聚乳酸-聚己内酯-醋酸纤维素(PCL-CA-PLLA)三维微-纳米复合纤维多孔支架材料。采用SEM分析聚合物比例、淬火时间、聚合物浓度和淬火温度等条件对纤维支架材料形貌影响。PCL-CA-PLLA(1∶1∶8)的直径为(276±121) nm，该直径与细胞外基质的尺寸大小(50~500 nm)相当，孔隙率和比表面积分别为95.12%和54.18 m²/g。说明PCL-CA-PLLA三维微-纳米复合纤维多孔支架材料为高孔隙率和大比表面积的三维多孔材料。与纯PLLA纤维支架材料相比，PCL-CA-PLLA三维微-纳米复合纤维多孔支架材料的机械强度有所提高，亲水性有所改善。PCL-CA-PLLA三维微-纳米复合纤维有望成为理想的组织工程支架材料。
- 左旋聚乳酸 /
- 醋酸纤维素 /
- 聚己内酯 /
- 微-纳米纤维 /
- 支架 /
- 生物矿化活性
Abstract: 3D nanofiber scaffold composites in bone tissue engineering are promising. Poly(L-lactic acid)-polycaprolactone-cellulose acetate 3D composite micro-nanofibrous porous scaffolds were prepared by low-temperature phase separation, without the assistance of additives. The effects of PCL-CA-PLLA ratio, quenching time, polymer concentration and quenching temperature on the morphology of fibrous scaffolds were investigated by SEM. The diameter of PCL-CA-PLLA (1∶1∶8) is (276±121) nm, which is similar to the size of the extracellular matrix (50-500 nm), and the porosity and specific surface area are 95.12% and 54.18 m²/g, respectively. It is indicated that PCL-CA-PLLA 3D micro-nanofibrous porous scaffold composites are 3D porous materials with high porosity and large specific surface area. Compared with pure PLLA fibrous scaffolds, the mechanical strength and hydrophilicity of PCL-CA-PLLA 3D micro-nanofibrous porous scaffold composites are improved. PLLA-PCL-CA 3D micro-nanofibrous are expected to be ideal tissue engineering scaffold materials.
- poly(L-lactic acid) /
- cellulose acetate /
- polycaprolactone /
- micro-nanofibrous /
- scaffolds /
- bio-mineralization activity

HTML全文

复合管多用于海洋油气输送，其中非粘接的钢带缠绕增强复合管多用于浅海油气运输^[1-3]。钢带缠绕增强复合管不仅克服了一般热塑性复合管质量密度低的缺点，且具有顺应性高、生产安装费用低及可再回收利用等特点^[4]。但长期恶劣的服役环境极易造成管道失效，进而引发油气泄露事故^[5]，因此开展海底复合管力学行为研究对钢带缠绕增强复合管结构设计、安全评价、操作维修等具有重要意义。

许多学者对钢带缠绕增强复合管进行了探索研究，如Bai等^[6-7]利用压溃试验和数值模拟研究发现，初始椭圆度、径厚比越大，钢带缠绕增强复合管极限抗外压能力越低。Bai等^[8]、Jiang等^[9]和Bai等^[10]利用轴向拉伸试验和数值模拟对钢带缠绕增强复合管进行研究发现，在纯拉伸载荷作用下，钢带缠绕增强复合管的拉伸刚度随着伸长量的增大而减小；同时建立了相应的解析模型并进行求解。Liu等^[11]基于蒙特卡洛(Monte-Carlo)及一次二阶矩(FOSM)相组合的方法矫正了钢带缠绕增强复合管的设计安全系数。学者们对复杂载荷下其他类型复合管进行了研究，如姜豪等^[12]建立了深海非粘结柔性管力学模型，分析了其在组合载荷工况下的力学性能。Gong等^[13]、Sertã等^[14]和Fe´ret等^[15]预测了深海柔性管的铠装层在轴向压缩、弯曲及外压下的屈曲失效。Bathtui^[16]给出用于模拟非粘结柔性立管在轴向拉伸、弯矩、内外压作用下结构响应的简化本构模型。Ramos等^[17]建立了深海柔性管在弯曲、扭转等组合载荷条件下的全滑动力学模型并得到相应解。Ramos等^[18]考虑管道层间间隙，提出了组合载荷下深海柔性管力学响应的计算模型，并进行了相应试验。Merino等^[19]采用试验和有限元方法研究发现，深海柔性管在内外压及拉伸条件下为线性响应，扭转载荷下为非线性响应。Gong等^[20]研究了深水夹芯管屈曲传播特性，提出了非粘接下深水夹芯管系统的传播压力经验表达式。Xue等^[21-23]对海底腐蚀管道在外部静水压力作用下的稳态屈曲拓展现象进行了非线性有限元分析。同时，提出一种夹芯管屈曲传播的三维分析方法，从壳的塑性稳定性理论角度描述了一种屈曲传播现象的综合机制，并提出了夹芯管的一阶剪切变形理论，推导了非浅水区夹芯层圆柱壳的平衡微分方程。

综上所述，目前针对钢带缠绕增强复合管的力学响应研究大多限于单一载荷下的试验或数值模拟，而对复杂载荷条件下的力学响应问题研究较少。由于海洋环境复杂多变，海底管道服役环境恶劣，钢带缠绕增强复合管承受复杂载荷，包括轴向拉力、弯曲载荷及内外压等，会加速管道失效。因此，本文开展多种复杂载荷下钢带缠绕增强复合管的力学特性研究。

1. 数值计算模型及验证

钢带缠绕增强复合管包含防漏和耐腐蚀的内层聚乙烯(PE)管、抵抗内外压的两层螺旋方向相反的钢质增强带、减小摩擦的保护层及抵抗外腐蚀的外层聚乙烯(PE)管^[24]，如图1所示。以长度为1 100 mm的钢带缠绕增强复合管为研究对象，建立如图1所示的数值计算模型。其中：1为内层PE管；2为内层缠绕钢带；3为外层缠绕钢带；4为保护层；5为外层PE管。

图 1 钢带缠绕增强复合管结构及数值计算模型

Figure 1. Structure and numerical calculation model of reinforced composite pipe wound with steel strip

PE—Polyethylene

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由于钢带缠绕增强复合管各层之间存在非线性接触，因此对较厚的内、外PE管采用C3D8R实体单元，对较薄的钢带及保护层采用S4R壳单元。接触关系采用法向硬接触和切向罚接触^[24]，钢带之间的摩擦系数为0.18，钢带与PE管之间的摩擦系数为0.22。管道一端完全固定，另一端施加轴向拉伸位移。根据文献[8]的试件，设置如表1所示的几何参数及材料属性。

表 1 钢带缠绕增强复合管的几何模型及材料参数

Table 1. Geometric and material parameters of reinforced composite pipe wound with steel strip

Model	Inner ring radius/mm	Thickness/mm	Helix angle/(°)	Width/mm	E/GPa	μ	Yield strength/MPa
Inner PE pipe	25.0	6.0	—	—	1.04	0.40	20
Inner steel strip	31.0	0.5	54.7	52	199.00	0.26	850
Outer steel strip	31.5	0.5	−54.7	52	199.00	0.26	850
Protective layer	32.0	1.0	—	—	1.04	0.40	20
Outer PE pipe	33.0	4.0	—	—	1.04	0.40	20
Notes: E—Elastic modulus; μ—Poisson’s ratio.

下载: 导出CSV

| 显示表格

文献[24]提出了计算钢带缠绕增强复合管轴向拉伸刚度的简化解析模型，可知钢带轴向拉力为

$\left\{ \begin{array}{l} {F_{{\rm{steel}},i}} = nbtE\cos \theta \cdot \left( {\dfrac{{\Delta L}}{L}{{\cos }^2}\theta + \dfrac{{{u_{{\rm{R}}i}}}}{{{R_{{\rm{m}}i}}}}{{\sin }^2}\theta } \right){\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} \left\{ {i = {\rm{1,}}2} \right\}\\ {u_{{\rm{R}}i}} = - \dfrac{{{{\rm{\Lambda }}_1}{\Lambda _5} + {\Lambda _6}}}{{1 + {\Lambda _2}{\Lambda _5}}}\\ {\Lambda _1} = \beta E{\sin ^2}\theta \cdot t\dfrac{{\Delta L{{\cos }^2}\theta }}{L}\left( {\dfrac{1}{{{R_{{\rm{m}}1}}}} + \dfrac{1}{{{R_{{\rm{m}}2}}}}} \right)\\ {\Lambda _2} = \beta E{\sin ^4}\theta \cdot t\left( {\dfrac{1}{{R_{{\rm{m}}1}^2}} + \dfrac{1}{{R_{{\rm{m}}2}^2}}} \right)\\ {\Lambda _5} = \dfrac{{\left( {1 + \nu } \right){R_6}\left[ {\left( {1 - 2\nu } \right)R_6^2 + R_7^2} \right]}}{{{E_{\rm{S}}}\left( {R_6^2 - R_7^2} \right)}}\\ {\Lambda _6} = \dfrac{{2\left( {1 - {\nu ^2}} \right){P_{{\rm{out}}}}R_6^2R_7^2}}{{{E_{\rm{S}}}\left( {R_6^2 - R_7^2} \right)}} + \nu \dfrac{{{R_6}\Delta L}}{L}\\[-14pt] \end{array} \right.$

(1)

式中：u_Ri为径向位移量；β为考虑间隙时的折减系数；E为钢带弹性模量；θ为钢带缠绕螺旋角度；L为管道长度；∆L为拉伸长度；n为同一层增强层中钢带的条数；b为带宽；R_mi为第i层钢带增强层的平均缠绕半径；t为钢带厚度；R₆为内层PE管外半径；R₇为外层PE管内半径；E_S为PE材料在当前加载步下的割线模量。

PE管的轴向拉力F_PEi为

${F_{{\rm{PE}}i}} = \frac{{{E_{\rm{S}}}{A_{0i}}\Delta L}}{{\Delta L + L}}$

(2)

式中，A_0i为PE管截面初始面积。

钢带缠绕增强复合管总轴向拉力F_T可看作管道各层贡献值的累加，即

${F_{\rm{T}}} = \Sigma {F_{{\rm{PE}}}} + \Sigma {F_{{\rm{steel}}}}$

(3)

图2为钢带缠绕增强复合管数值模型与实验及解析解对比。可知，将数值计算模型与文献[8]的试验结果及文献[24]的解析模型进行对比，三者变化趋势一致。同时，本文数值计算模型比解析模型更接近试验值，这是由于解析模型未考虑层与层之间的摩擦作用及螺旋钢带自身弯曲变化，即仅考虑钢带沿带长度方向的轴向变形。因此，该数值计算模型较为可靠。

图 2 钢带缠绕增强复合管数值模型与试验及解析解对比

Figure 2. Comparison of numerical model, experimental and analytical model results of reinforced composite pipe wound with steel strip

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2. 不同组合载荷下钢带缠绕增强复合管的力学性能

为研究由拉伸、内外压和弯曲载荷组合的复杂载荷下带缠绕增强复合管的力学性能，其组合类型为：内外压加拉伸、内外压加弯曲、内外压加弯曲及拉伸，同时与纯拉伸和纯弯曲载荷条件进行对比。由于海底工况复杂，带缠绕增强复合管受载具有不确定性，因此本文选取的加载路径为在同一分析步中同时施加内外压、拉伸或弯曲载荷。承载能力可通过管道屈曲时的载荷大小判定，载荷越大，承载性能越好。钢带缠绕增强复合管的拉伸刚度为

$k = \frac{F}{x}$

(4)

式中：k为拉伸刚度；F为轴向拉力；x为轴向位移。

钢带缠绕增强复合管的弯曲刚度为

$m = \frac{M}{\alpha }$

(5)

式中：m为弯曲刚度；M为弯矩；α为弯曲角度。

图3为钢带缠绕增强复合管轴向拉力和拉伸量的关系曲线。可知，在弹性阶段(AB、AC、AD段)，钢带缠绕增强复合管的拉伸刚度不变。在BE、DF、CG段，钢带缠绕增强复合管的拉伸刚度随伸长量增大而减小，非线性特征明显，将该阶段定义为过渡阶段。而EH、FI、GJ段则为整体的屈服阶段。曲线Ⅰ(内压为1 MPa、外压为3 MPa)和曲线Ⅱ(内压为2 MPa、外压为3 MPa)的拉伸刚度明显小于纯拉伸情况，这是由外压大于内压，压差引起泊松效应(一端固定条件下，钢带缠绕增强复合管因挤压而径向收缩，又因整体体积不变，钢带缠绕增强复合管将沿自由端方向伸长)造成的。在曲线Ⅰ基础上，对自由端施加0.2 rad的转角位移，钢带缠绕增强复合管被拉伸约至77 mm时其拉力急剧下降，此时钢带缠绕增强复合管失效。可以看出，弯曲载荷对钢带缠绕增强复合管拉伸刚度影响较小，但会降低钢带缠绕增强复合管屈曲时的临界拉力，即抗拉承载能力降低。

图 3 不同拉伸载荷作用下钢带缠绕增强复合管的力学性能

Figure 3. Mechanical properties of reinforced composite pipe wound with steel strip under different tensile loads

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图4为钢带缠绕增强复合管的弯矩和弯曲角度关系曲线。可知，曲线Ⅰ(内压为1 MPa、外压为3 MPa)和曲线Ⅱ(内压为2 MPa、外压为3 MPa)的钢带缠绕增强复合管弯曲刚度明显小于纯弯曲情况。这是由于钢带缠绕增强复合管不受内外压作用时，层间挤压较小，最大静摩擦力小；在弯曲过程中各层易产生相对滑移，滑动摩擦力在一定程度上阻碍钢带缠绕增强复合管变形，使钢带缠绕增强复合管产生更大弯矩，即迟滞效应。同理，钢带缠绕增强复合管承受内外压时，层间摩擦力增强，无滑移现象，钢带缠绕增强复合管整体性提高。在曲线Ⅰ基础上，钢带缠绕增强复合管被拉伸至60 mm，轴向拉力所形成的弯矩与初始弯矩叠加，使在相同弯曲形变下钢带缠绕增强复合管弯曲刚度大幅提高，柔性降低。

图 4 不同弯曲载荷作用下钢带缠绕增强复合管的力学性能

Figure 4. Mechanical properties of reinforced composite pipe wound with steel strip under different bending loads

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当钢带缠绕增强复合管承受较大内外压时，虽然钢带缠绕增强复合管整体性增强，但由于钢带缠绕增强复合管各层力学性能不同，形变过程中外层PE管易提前进入屈服阶段，使钢带缠绕增强复合管整体弯曲刚度下降，管端弯矩出现极大值，如曲线Ⅰ和Ⅱ所示。

3. 复杂载荷下钢带缠绕增强复合管各层力学性能对比

3.1 内层和外层PE管的力学性能

图5为内层和外层PE管在纯拉伸和组合拉伸(包含内外压和弯曲，且以拉伸载荷为主)载荷作用下的应力云图。可见，纯拉伸作用下应力沿管道分布较均匀，两端应力小于中间段。内层PE管出现螺旋状高应力区，这是由于拉伸过程中钢带边缘对其径向挤压。而在组合拉伸作用下，相同拉伸长度的内层和外层PE管在自由端附近产生严重的屈曲破坏，进入失效状态。

图 5 内层和外层聚乙烯(PE)管在纯拉伸和组合拉伸下的应力分布

Figure 5. Stress distributions of inner and outer polyethylene (PE) pipes under pure tensile and combined tensile loads

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图6为内层和外层PE管在纯拉伸和组合拉伸作用下应力及应变随拉伸量的变化。由图6(a)可知，纯拉伸载荷作用时，轴向位移为0~90 mm范围内的应变呈线性变化，复合管处于弹性状态，且内层和外层PE管应变基本一致。在组合拉伸下，内层和外层PE管在拉伸至77 mm时应变急剧增大，达到屈服极限，开始产生塑性变形，且外层PE管应变大于内层PE管。由图6(b)可知，当拉伸至76.5 mm时，外层PE管的最大Mises应力达到22.60 MPa，内层PE管为21.51 MPa，进一步说明在组合拉伸的条件下，外层PE管力学响应较内层PE管更为敏感。

图 6 内层和外层PE管在纯拉伸和组合拉伸作用下的应力和应变

Figure 6. Stress and strain of inner and outer PE pipes under pure tensile and combined tensile loads

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外层PE管应力分布如图6(a)内图所示。可知，在拉伸过程中管道自由端上部出现高应力区，外层PE管螺旋状高应力区的应力值逐渐增大，最终在拉伸约至77 mm时，外层PE管在自由端附近发生屈曲失效。

图7为内层和外层PE管在纯弯曲和组合弯曲(包含内外压和拉伸，且以弯曲载荷为主)作用下的应力云图。可见，在纯弯曲作用下，高应力区出现在管道固定端附近上部。而在组合弯曲作用下的高应力区出现在管道自由端附近，并发生屈曲破坏。同时外层PE管应力分布较内层PE管更具规律性。

图 7 内层和外层PE管在纯弯曲和组合弯曲下的应力分布

Figure 7. Stress distribution of inner and outer PE pipes under pure bending loads and combined bending loads

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图8为内层和外层PE管在纯弯曲和组合弯曲作用下的应力和应变随弯曲角度的变化。由图8(a)可知，在纯弯曲作用下，内层和外层PE管均处于弹性阶段；在组合弯曲载荷作用下，内层和外层PE管的应变在弯曲角度分别为0.24 rad和0.25 rad时急剧增加，外层PE管提前失效。由图8(b)可知，无论是在纯弯曲载荷作用下还是组合弯曲载荷作用下，外层PE管的Mises应力始终大于内层PE管。

图 8 内层和外层PE管在纯弯曲和组合弯曲作用下应力和应变

Figure 8. Stress and strain of inner and outer PE pipes under pure bending and combined bending loads

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外层PE管应力分布如图8(a)内图所示。可知，钢带缠绕增强复合管变形过程中外层PE管的高应力区不断向自由端集中，并在其附近发生屈曲破坏。管道整体曲率半径非常大，说明在组合弯曲载荷作用下钢带缠绕增强复合管弯曲刚度大幅度提高，柔性降低。

3.2 钢带增强层的力学性能

图9为组合拉伸载荷和组合弯曲载荷作用下内层缠绕钢带的应力云图。可见，钢带在组合拉伸载荷和组合弯曲载荷作用下应力分布几乎一致。应力沿轴向方向呈非均匀分布，这是由于边界条件的非线性即端部效应，钢带在边缘部分出现应力集中造成的。同时，应力集中区域沿某一路径具有对称性。创建相应路径及节点编号1~7，提取一组单元在同一时刻对应节点的Mises应力，如图9所示。由文献[8]可知，纯拉伸下内层钢带对称应力的路径平行于带宽分布，而组合拉伸载荷和组合弯曲载荷作用下的路径发生偏移，说明复杂载荷会改变内层钢带对称应力分布路径。

图 9 内层缠绕钢带应力云图及节点Mises应力

Figure 9. Stress cloud diagram of inner wound steel strip and Mises stress of nodes

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4. 参数敏感性分析

4.1 钢带螺旋角度

选取钢带缠绕增强复合管中钢带增强层的三种螺旋角度(±54.7°、±60.5°、±67.7°)进行分析。图10为组合拉伸载荷作用下螺旋角对钢带缠绕增强复合管拉伸性能的影响。可见，随着螺旋角度增大，由于未发生层间相对滑动，钢带缠绕增强复合管在弹性阶段的拉伸刚度几乎不发生变化；在过渡及屈服阶段，钢带缠绕增强复合管的拉伸刚度增大，柔性降低，这是由于螺旋角度的增大，增加了单位轴向长度内钢带缠绕圈数，导致钢带覆盖率提高，总摩擦力增大，钢带缠绕增强复合管各层之间不易产生滑移。随着螺旋角增大，钢带缠绕增强复合管屈曲时的临界拉力增大，抗拉承载能力提高。

图 10 组合拉伸载荷作用下螺旋角对钢带缠绕增强复合管拉伸性能影响

Figure 10. Effect of helix angles on tensile properties of reinforced composite pipe wound with steel strip under combined tensile load

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图11为组合弯曲载荷作用下螺旋角对钢带缠绕增强复合管弯曲性能影响。可见，随着螺旋角度增大，钢带缠绕增强复合管在弹性阶段的弯曲刚度基本不变；在屈服阶段，钢带缠绕增强复合管弯曲刚度随螺旋角增大而增大，柔性降低，这是由于螺旋角度越大，在保持钢带宽度不变条件下，单位轴向长度内钢带缠绕圈数增大，即钢带覆盖率越高，钢带缠绕增强复合管整体刚度越大；钢带缠绕增强复合管屈曲时的临界弯矩呈非单调变化，存在极大值，当弯曲角度为0.215 rad时，螺旋角为60.5°的钢带缠绕增强复合管弯矩为697 kN·m，载荷达到屈曲临界值，而螺旋角为54.7°的钢带缠绕增强复合管仍处于屈服阶段，螺旋角为67.7°的钢带缠绕增强复合管早已失效。

图 11 组合弯曲载荷作用下螺旋角对钢带缠绕增强复合管弯曲性能影响

Figure 11. Effect of helix angles on bending properties of reinforced composite pipe wound with steel strip under combined bending load

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4.2 层间摩擦系数

图12为组合拉伸载荷作用下摩擦系数对钢带缠绕增强复合管拉伸性能的影响。可知，在组合拉伸载荷作用下，随着摩擦系数增大，钢带缠绕增强复合管在弹性阶段轴向拉伸刚度基本不变，体现了较强整体性；在过渡阶段，钢带缠绕增强复合管拉伸刚度提高，柔性降低，这是由于摩擦系数的增大提高了层间滑动摩擦力，迟滞效应更加明显；钢带缠绕增强复合管屈曲时的临界拉力增大，抗拉承载能力提高，即当摩擦系数为0.2时，钢带缠绕增强复合管在拉伸至77 mm时失效，而对于其他情况，其失效时的拉伸量均小于77 mm。

图 12 组合拉伸载荷作用下摩擦系数对钢带缠绕增强复合管拉伸性能的影响

Figure 12. Effect of friction coefficients on tensile properties of reinforced composite pipe wound with steel strip under combined tensile load

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图13为组合弯曲下摩擦系数对钢带缠绕增强复合管弯曲性能影响。可见，随着摩擦系数增大，弹性阶段的钢带缠绕增强复合管与组合拉伸载荷作用下刚度的变化规律类似。钢带缠绕增强复合管屈曲时的临界弯矩逐渐增大，抗弯承载能力提高。

图 13 组合弯曲下摩擦系数对钢带缠绕增强复合管弯曲性能影响

Figure 13. Effect of friction coefficients on bending properties of reinforced composite pipe wound with steel strip under combined bending load

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5. 结论

(1)压差(外压大于内压，且≤2 MPa)越大，钢带缠绕增强复合管柔性越高；钢带缠绕增强复合管弯矩存在极大值。与纯拉伸作用相比，组合拉伸载荷作用时钢带缠绕增强复合管屈服时的临界拉力降低，抗拉承载能力降低；与纯弯曲作用相比，组合弯曲载荷作用时钢带缠绕增强复合管柔性大幅降低。

(2)复杂载荷作用的高应力区出现在钢带缠绕增强复合管自由端附近，并在此处发生屈曲失效，且外层聚乙烯(PE)管的应变大于内层PE管；而在纯弯曲载荷作用下，高应力区出现在钢带缠绕增强复合管的固定端，纯拉伸载荷作用下应力分布较均匀；复杂载荷会改变内层钢带对称应力的分布路径。

(3)复杂载荷作用下，钢带螺旋角度及摩擦系数越大，钢带缠绕增强复合管柔性越低。在组合拉伸载荷作用下，增大钢带螺旋角及层间摩擦系数，钢带缠绕增强复合管屈曲时的临界拉力增大，承载能力提高。在组合弯曲载荷作用下，螺旋角增大使钢带缠绕增强复合管屈曲时的临界弯矩呈非单调变化，存在极大值；层间摩擦系数越大，临界弯矩越大，钢带缠绕增强复合管的抗弯承载能力提高。

图 1 不同溶剂的PCL-CA-PLLA复合材料的SEM图像

Figure 1. SEM images of PCL-CA-PLLA composites with diffierent solvents((a) DO; (b) Acetonitrile; (c) DMAc; (d) THF)

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图 2 不同质量比的PCL-CA-PLLA三维微-纳米复合纤维扫描电镜图(其余条件参见表1)

Figure 2. SEM images of PCL-CA-PLLA 3D composites micro-nanofibrous with different mass ratio of PCL-CA-PLLA， (a) 1:1:8，(b) 1.5:1.5:7.5，(c) 2:2:6，(d) 2.5:2.5:6

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图 3 不同淬火时间PCL-CA-PLLA微-纳米复合纤维的SEM图像

Figure 3. SEM images of PCL-CA-PLLA composite micro-nanofibrous with different quenching time ((a) 1 min; (b) 3 min; (c) 5 min; (d) 10 min; (e) 30 min; (f) 60 min)

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图 4 不同聚合物浓度PCL-CA-PLLA微-纳米复合纤维的SEM图像

Figure 4. SEM images of PCL-CA-PLLA composite micro-nanofibrous with different polymer concentrations ((a) 3%; (b) 5%; (c) 7%; (d) 9%; (e) 12%)

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图 5 不同淬火温度PCL-CA-PLLA微-纳米复合纤维的SEM图像

Figure 5. SEM images of PCL-CA-PLLA composite micro-nanofibrous at different quenching temperatures((a) 10℃; (b) 0℃; (c) −10℃; (d) −20℃; (e) -30℃)

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图 6 不同质量比PCL-CA-PLLA微-纳米复合纤维的XRE图谱 (a) 和DSC曲线 (b)

Figure 6. XRD patterns (a) and DSC curves (b) of PCL-CA-PLLA composite micro-nanofibrous with different mass ratios of PCL-CA-PLLA

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图 7 PCL-CA-PLLA微-纳米复合纤维的N₂吸附-脱附等温线 (a) 和孔容-孔径分布 (b)

Figure 7. N₂ absorption-desorption isotherms (a) and pore size distribution curve (b) of PCL-CA-PLLA composite micro-nanofibrous

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图 8 PCL-CA-PLLA微-纳米复合纤维压缩强度和冲击强度

Figure 8. Compressive strength and impact strength of PCL-CA-PLLA composite micro-nanofibrous

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图 9 PCL-CA-PLLA微-纳米复合纤维支架浸泡在模拟体液(SBF)中14天的SEM图像

Figure 9. SEM images of PCL-CA-PLLA composite micro-nanofibrous scaffolds immersion in simulated body fluid (SBF) with 14 days ((a) Before immersion (PLLA); (b) After immersion (PLLA); (c) Before immersion (PCL-CA-PLLA); (d) After immersion (PCL-CA-PLLA))

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表 1 左旋聚乳酸-聚己内酯-醋酸纤维素 (PCL-CA-PLLA)微-纳米纤维的制备条件

Table 1 Preparation condition of polycaprolactone-cellulose acetate-poly(L-lactic acid) (PCL-CA-PLLA) micro-nanofibrous

Experimental condition	Solvent	Mass ratio of PCL∶CA∶PLLA	Concentration/wt%	Quenching time/min	Quenching temperature/℃
1	DO, Acetonitrile, DMAc, THF	1∶1∶8	7	120	−30
2	THF	1∶1∶8, 1.5∶1.5∶7, 2∶2∶6, 2.5∶2.5∶5	7	120	−30
3	THF	1:1:8	7	1, 3, 5, 10, 30, 60	−30
4	THF	1:1:8	3, 5, 7, 9, 12	60	−30
5	THF	1∶1∶8	7	60	10, 0, −10, −20, −30
Notes: DO—1,4-dioxane; DMAc—N,N-dimethylacetamide; THF—Tetrahydrofuran.

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表 2 溶剂和聚合物溶解度参数

Table 2 Solubility parameters of solvents and polymers

Solvent or polymer	Solubility parameter/(J·cm⁻³)^1/2
DO	20.3
Acetonitrile	24.5
DMAc	22.8
THF	18.5
PLLA	20.1
PCL	22.2
CA	21.1

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表 3 PCL-CA-PLLA微-纳米复合纤维的热力学参数

Table 3 Thermal parameters of PCL-CA-PLLA composite micro-nanofibrous

Mass ratio of PCL∶CA∶PLLA	T_m of PCL/℃	T_m of PLLA/℃	ΔH_m of PCL/(J·g⁻¹)	Χ_c of PCL/%	ΔH_m of PLLA/(J·g⁻¹)	Χ_c of PLLA/%
0∶0∶10	−	169.80	−	−	−42.74	45.66
1∶1∶8	57.98	169.01	−4.88	35.10	−34.62	46.23
1.5∶1.5∶7	56.46	169.01	−7.23	34.67	−28.88	44.08
2∶2∶6	56.22	168.90	−10.13	36.43	−25.38	45.19
2.5∶2.5∶5	57.48	168.84	−12.66	36.43	−21.10	45.09
Notes: T_m—Melting temperature; ΔH_m—Melting enthalpy; Χ_c—Degree of crystallinity.

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表 4 PCL-CA-PLLA微-纳米复合纤维各物理参数

Table 4 Physics parameters of PCL-CA-PLLA composite micro-nanofibrous

Mass ratio of PCL∶CA∶PLLA	Water contact angle/(°)	Porosity/%	Water absorption/%	Specific surface area/(m²·g⁻¹)
0∶0∶10	127.1±3.1	94.13	6.13	52.46
1∶1∶8	93.1±4.1	95.12	11.15	54.18
1.5∶1.5∶7	83.1±2.4	90.10	13.29	46.14
2∶2∶6	76.3±2.1	88.23	15.33	45.22
2.5∶2.5∶5	70.2±1.6	90.11	16.19	40.13

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