贴肤用熔喷非织造材料柔韧化改性及应用研究进展

2023-07-04 00:52秦子轩张恒甄琪李晗王镕琛宋卫民
丝绸 2023年3期

秦子轩 张恒 甄琪 李晗 王镕琛 宋卫民

摘要: 熔喷非织造材料是一种由超细纤维直接组成的柔性多孔介质,具有纤维比表面积大、结构蓬松和屏蔽性好等特点,在医疗防护和个人卫生等贴肤领域中具有广泛应用。然而,由于部分熔喷非织造原料的固有脆性,导致熔喷非织造材料存在柔软舒适性差的问题。因此,提升熔喷非织造材料柔韧性,已经成为贴肤用纺织品领域的研究热点。本文整理熔喷聚合物原料共聚改性和共混改性研究进展,介绍了熔喷非织造生产工艺对材料柔韧性影响规律,阐述了熔喷非织造材料在柔性贴肤领域应用形式,为熔喷非织造材料柔韧性提升与贴肤性应用提供研究思路。

关键词: 熔喷;非织造材料;柔韧化改性;共聚改性;共混改性;贴肤应用

中图分类号: TS176

文献标志码: A

文章编号: 1001-7003(2023)03-0073-09

引用页码:

031110

DOI: 10.3969/j.issn.1001-7003.2023.03.010(篇序)

熔喷非织造材料具有纤维线密度小、孔隙率高和质地柔软等特点[1-3],在医疗防护(口罩、防护服等)[4]、个人卫生(面膜、湿巾等)[5]和智能调温(服装、家纺等)[6]等贴肤产品领域发挥着重要作用。在医疗防护领域,熔喷非织造材料所制备的口罩类医疗防护装备,具备屏蔽细菌和过滤病毒等特性,在抗击新型冠状病毒肺炎(COVID-19)疫情中有效阻断了病毒扩散与传播;在卫生用品领域,熔喷非织造材料因具有材质轻和结构蓬松等特点,在湿巾和尿不湿等产品中应用广泛。

目前,熔喷非织造原料以聚丙烯(PP)、聚乙烯(PE)为主,且随着人们环保意识不断增强,聚乳酸(PLA)等新型可降解聚合物受到越来越多学者关注[7-9],这为熔喷非织造材料新产品开发和应用带来了新契机。然而,熔喷非织造材料用聚合物原料中含有较多刚性分子链段,从而导致非织造材料脆性较大且柔韧性差,限制了其在贴肤领域的应用,而通过对熔喷非织造用聚合物原料进行化学改性(共聚)或物理改性(共混),向聚合物大分子链中引入柔性分子链段或添加柔性聚合物,可以有效改善材料硬度[10],满足人们对于舒适性能的需求。因此,探究采用共聚和共混改性的方法降低聚合物原料中分子链刚性,提升熔喷非织造材料柔韧性,并进一步实现贴肤性应用具有十分重要的意义。

此外,聚合物原料在熔喷工艺中因加工温度、加工流程等导致其在应用方面的局限性(脆性大、舒适性不足等)进一步加大。基于此,本文综述了针对不同熔喷非织造材料用聚合物原料的柔韧化改性方法研究进展,列举了柔软母粒在提升熔喷非织造材料柔韧性的应用概况,并简述了熔喷工艺特性和贴肤性应用,以期为熔喷非织造材料柔韧性提升和贴肤性应用开发提供参考和思路。

1 熔喷非织造材料原料柔韧化改性

熔喷非织造技术起源于传统聚合物熔体纺丝,将单一或多种聚合物原料均匀混合后喂入螺杆挤出装置,高温熔融形成聚合物熔体后,在模头处经高速热空气充分牵伸,由喷丝孔喷出,快速冷却成纤后,均勻铺网,形成非织造纤维材料,熔喷非织造生产工艺流程如图1所示。相较于其他非织造材料成型工艺,熔喷工艺用聚合物原料具有较高熔融流动指数(MFI),同时其相对分子质量分布较窄、熔融黏度较低,这不仅有助于聚合物熔体充分牵伸成纤,而且能够引入其他物质来改善非织造材料柔韧性。因此,到目前为止,在熔喷工艺中对聚合物原料进行共聚和共混改性[11-13]提高聚合物柔韧性,是熔喷非织造原料柔韧化改性的常用方法之一。

1.1 共聚改性

共聚改性是通过化学反应向聚合物大分子主链上引入某些特定作用分子链段,从而改变聚合物分子结构,并达到提高聚合物分子链柔韧性目的[14]。常用柔韧性分子链段主要包括马来酸酐和甲基丙烯酸缩水甘油酯等,如表1所示。

Zhang等[21]在PLA-PEG-PLA共聚物(图2(a))制备过程中,探究了聚乙二醇(PEG)对PLA柔韧化改性效果,结果表明该共聚物可以提高PEG分子在PLA基体中分散性,从而有效提高PLA大分子链段运动能力,使材料具有更好的柔韧性。Theryo等[22]首先通过开环共聚方法制备了1,5-环辛二烯-co-5-降冰片烯-2-甲醇(PCN),然后侧链接枝PLA生成了PCNL共聚物(图2(b)),该样品断裂伸长率高达238%,比纯PLA材料提高了1 700%。Yu等[23]先将羧基接枝到PE分子链上生成m-LDPE,然后再以聚苯乙烯-甲基丙烯酸缩水甘油酯(SG)为主要接枝链,接枝生成PLLA/m-LDPE共混物。结果发现,PLLA和m-LDPE羧酸基可以与SG主链上环氧基团发生反应,使共混体系界面相容性提高(图2(c)),增容后共混物断裂伸长率由9%提高至367%。

通过上述研究发现,向聚合物大分子链段引入特定柔韧性分子链,能够有效提升聚合物分子链柔韧度。因此,共聚改性是一种提升聚合物柔韧性的有效方法。

1.2 共混改性

共混改性具有操作流程简便、生产成本低等优点,是改善聚合物柔韧性常用的物理改性方法,通常采用弹性体或低聚物等与聚合物进行熔融共混。一方面,基体中加入弹性体,利用其柔韧性分子链段分散在聚合物基体中,降低共混物刚性;另一方面,低聚物中小分子可以分散在基体分子链段中,削弱分子间作用力,提高聚合物分子运动能力,增加共混物柔韧性。

1.2.1 弹性体改性

热塑性聚氨酯弹性体(TPU)是由柔性软段和刚性硬段交替组成的聚合物,具有良好柔韧性和延展性[24]。有学者将TPU与PLA[25-26]等聚合物进行共混熔喷(图3(a)),制备出一种手感柔软的熔喷非织造材料。研究表明,TPU在纤维内以“岛”的形式存在,为柔韧性和延伸性改善提供了桥梁作用,并且样品柔韧性随着TPU含量增大而增大。随后,Zhang等[27]则以聚氨酯弹性体预聚体(PUEP)作为活性增容剂,对PLA/TPU进行增容共混改性(图3(b)(c)),加入PUEP后发现,共混体系界面相容性显著提高,共混物断裂伸长率提高至92.6%。

同理,Lin等[28]以聚丙烯接枝马来酸酐(PP-g-MA)为相容剂(图4),进行PP/TPU共混成型研究。结果发现,当共混物中TPU与PP-g-MA质量分数分别为20%和5%时,共混物样品较纯PP弹性提升了30%。综上,加入相容剂不仅有助于共混物形态稳定,同时共混物中加入TPU,其柔软性链段有助于改善PP与PLA刚性,促进PP/TPU和PLA/TPU等共混物柔韧性提升。

乙烯-辛烯弹性体(POE)与乙烯-醋酸弹性体(EVA)是辛烯软链段和醋酸软链段分别与乙烯结晶链段相互交联而制成的共聚物。赵洪等[29]探究了POE/PP复合材料的力学性能,发现复合材料结晶度随着POE含量增大而降低,当POE含量为40%时,复合材料形变量增大至11.25%,远大于纯PP的1.25%。同时,Chang等[30]研究了不同EVA含量对PP/EVA熔喷非织造材料性能影响,发现PP/EVA共混物具有良好热稳定性和流变性能,当EVA比例在5%~30%时,样品的断裂伸长率明显提高。

1.2.2 低聚物改性

低聚物与熔喷聚合物原料进行共混改性时,能够均匀分散在聚合物基体中,通过削弱分子间作用力,提高分子链运动能力,从而降低聚合物脆性。常用的低聚物有柠檬酸脂类和聚乙二醇等。为了探究不同檸檬酸酯类物质对聚乳酸柔韧化改性作用,尹静波等[31]分别采用乙酰柠檬酸三正丁酯(ATBC)、柠檬酸三正丁酯(TBC)、柠檬酸三乙酯(TEC)等与PLA进行共混。通过对样品分析后发现,柠檬酸酯类物质与PLA有良好相容性。当其添加量为10%~15%时,共混物的断裂伸长率较纯PLA提升了近40倍;同时,随着柠檬酸酯中醇相对分子质量越低,越有利于降低共混物玻璃化温度,从而提高其柔韧性。类似的,Guo等[32]研究了不同相对分子质量(600、2 000)聚乙二醇(PEG)对PLA改性效果。研究发现,PEG增强了PLA分子链段运动能力,当共混物中PEG含量为20%时,其断裂伸长率增大到370%~400%。

1.2.3 熔喷非织造材料用柔软母粒

在熔喷非织造材料实际生产中,加入一定比例柔软母粒能够增加熔喷非织造材料柔韧性。目前,柔软母粒一般由柔软剂、润滑剂、分散剂和弹性体等主要成分组成。同时,为满足材料多功能性需要,柔软母粒中还会含有抗菌剂、抗静电剂、阻燃剂等成分。柔软母粒功能及其种类如图5所示。

通过柔软母粒中多种组分协同作用,可以在实际生产中有效提升熔喷非织造材料柔韧性。如在专利《一种熔喷柔软母粒及其制备方法》中提供了一种包括硬脂酸酰胺、乙撑双硬脂酸酰胺、聚乙烯蜡和1-辛烯与乙烯等成分组成的柔软母粒。应用发现,该柔软母粒可以有效增加聚合物熔体韧性,为生产超细柔软熔喷非织造材料提供了技术支撑。专利《一种无纺布柔软母粒及其制备方法》则提供了一种可以快速发挥稳定作用的柔软母粒。该母粒以油酸酰胺和芥酸酰胺为润滑剂,在赋予熔喷非织造材料柔软手感的同时,也能保证其柔性作用的耐久性。专利《一种柔软母粒及其制备方法》提供了一种由壳聚糖、铜、铝和聚乙烯组成的母粒,该母粒同时具有柔韧性、抗菌和防霉等功能性。此外,专利《一种聚丙烯抗静电柔软母粒及其制备方法》中提到在聚丙烯柔软母粒中加入了抗静电剂成分,获得了一种制备聚丙烯非织造材料的抗静电柔软母粒。

图6为近十年来关于熔喷非织造材料柔软母粒专利在全球和中国的申请情况。从图6可以看出,全球专利申请数量有867篇,在中国专利数量有520篇。需要注意的是,2020年柔软母粒专利申请个数迎来了一个小高峰,国内申请数量达到81篇,全球申请数量为114篇。这可能是由于COVID-19爆发,导致全球范围内对医疗卫生防护产品及其柔软舒适性能的需求大幅增加。

2 成型工艺对非织造材料柔韧性影响规律

熔喷非织造材料在加工成型过程中,通过对接收距离(DCD)、热风压力、热风温度和模头温度等工艺参数调整,能够获得纤维直径更细,孔隙率更高和结构更蓬松的柔韧性非织造材料。Zhang等[33]和彭梦娜等[34]分别通过改变DCD和热风温度来研究非织造材料结构与性能。如图7所示,随着DCD从10 cm增加至30 cm,材料的孔隙率增大,结构变蓬松;对于PP/TPU非织造材料而言,随着热风温度不断升高,熔喷非织造材料主要纤维直径分布在6 μm以下,当热风温度从250 ℃升高到270 ℃时,PP/TPU熔喷非织造材料具有良好弹性回复和触觉柔韧性。Yesil[35]研究了DCD、热风压力和模头温度对聚乙烯(PE)熔喷非织造材料结构和力学性能影响(图8)。研究表明,随着DCD从15 cm增加到25 cm时,样品材料直径明显减小,而继续增加会由于空气冷却原因导致纤维直径很难再发生变化;风压增大,会使材料纤维直径减小的同时,结构也更加蓬松。此外,付小栓等[36-37]研究发现,熔喷工艺参数改变对非织造材料结构性能影响呈现出相同规律,即纤维直径会随着DCD和风压逐渐增大而减小,同时,模头温度在一定范围内逐渐升高,会提高材料流动性,有利于获得纤维直径更细的熔喷非织造材料。

通过对熔喷非织造生产工艺参数(DCD、热风压力、温度和模头温度等)进行调整,对非织造材料纤维细度和结构蓬松度等产生影响,进而改善材料柔韧性。从上述研究可以得出,在工艺参数范围内,DCD增加会使接收网帘纤维直径减小;热风压力及温度增高,有助于熔体细流得到充分牵伸,从而获得线密度更小的纤维。而对于非织造材料而言,固定其他参数不变的情况下,纤维直径越小,使得材料厚度越小,蓬松度与孔隙率越高,材料柔韧性也就越好。因此,通过研究工艺参数的调控对非织造材料结构和性能影响,能够为进一步改善熔喷非织造材料柔软舒适性及开发贴肤用非织造材料提供参考。

3 熔喷非织造材料贴肤性应用

熔喷非织造材料在防护服、口罩和面膜等贴肤领域具有广泛应用前景,已成为近年来熔喷非织造材料的重点应用方向。图9为熔喷非织造材料贴肤应用场景。

3.1 医疗防护用品

熔喷非织造材料具有优异屏蔽性、过滤性和透气性[38],被广泛用于口罩、防护服和手术服等医疗防护装备。专利《一种口罩非织造布及工艺》采用PP熔喷非织造材料生产一种医疗防护用口罩,该产品不仅可以屏蔽病毒,同时使用过程中也能给人带来柔软贴肤的舒适感。此外,專利《防护服用原材料和防护服》利用熔喷非织造材料纤维线密度小、结构蓬松等特性,制造了一种透气性良好、质量轻和手感柔软的医用防护服装备,解决了传统防护服穿着舒适性不足和柔软贴肤性差等问题。随着生物可降解聚合物不断发展,也为熔喷非织造材料在医疗领域带来更多应用前景。如彭鹏等[39]以聚乳酸为原料,通过熔喷工艺制备了一种超细纤维医用敷料,测试证明,该材料纤维直径主要为2~5 μm,具有透气性好,贴肤柔软的同时具有很好的抗菌效果,对人体无毒副作用。

3.2 卫生用品

随着人们生活水平不断提高,使得熔喷非织造材料在卫生用品领域柔性应用也越来越广泛。专利《一种超柔软贴肤面膜专用非织造布及其制造方法》为了解决当前面膜基布存在贴肤性差等问题,采用PP与丙烯基弹性体为原料,生产了一种柔软贴肤性好的熔喷非织造材料,该材料具有柔韧性高、密度小和贴肤性好等特点。为了提升熔喷非织造材料柔韧性,扩大其在卫生用品领域应用,专利《一种柔性和透气性较好的卫生用品及复合无纺布》则制得了一种以柔韧性优异的熔喷非织造材料为主的卫生用品,该熔喷材料兼具有拒水和抗菌效果。

3.3 保暖材料

熔喷法非织造材料纤维线密度小,会使材料孔隙率增大,较多孔隙可以使材料内部储存空气,起到保温隔热效果。仇何等[40]使用聚乳酸与聚酰胺弹性体为原料,通过将制备的熔喷超细纤维喷覆在直径25 μm的长丝上,获得具有类似鹅绒结构的保暖材料,这类材料在具有良好保暖效果的同时,也拥有柔韧性好、亲肤的特点,可以广泛地应用于服装,家纺等产品。

因此,通过上述分析可以发现,熔喷非织造材料在医疗(口罩和防护服等)、个人卫生(面膜和湿巾等)及保暖材料(服装、家纺填充物)等贴肤领域应用越来越广泛。同时,这也对探究柔韧化改性熔喷非织造材料在贴肤应用领域开发与推广具有重要意义。

4 结 语

近年来,熔喷非织造材料作为一种超细纤维材料,在医疗防护和个人卫生等贴肤领域应用越来越广泛。而在熔喷非织造材料开发应用中,还存在脆性较大、柔软舒适度不足等。因此,在提升熔喷非织材料柔韧性过程中,还存在一些亟须解决的问题:一方面,可用于熔喷非织造的聚合物种类繁多,需要采用不同的方法(化学或物理)来提升材料柔韧性,而目前较多的研究方法仍旧处于实验阶段。因此,不仅要选择合适的方法提高材料柔韧性,同时也要遵循操作简便、成本低及可工业量产化等原则。另一方面,提升熔喷非织材料柔韧性能是提高其在贴肤材料领域应用的前提,为了更好满足人们对美好生活需求,就要对熔喷非织造材料多样化的功能性应用提升投入更多研究,这也会成为熔喷非织材料的未来发展方向。

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Research progress of flexible modification and applications of skin-fitting melt-blown nonwovens

QIN Zixuan1a, ZHANG Heng1a, ZHEN Qi1b, LI Han1a, WANG Rongchen1a, SONG Weimin2

(1a.College of Textiles; 1b.College of Fashion Technology, Zhongyuan University of Technology, Zhengzhou 451191, China;2.Suzhou Doro New Material Technology Co., Ltd., Suzhou 215600, China)

Abstract:

Melt-blown nonwovens, flexible porous media made up directly of superfine fibers, not only have a large fiber specific surface area, fluffy structure and good shielding properties, but also have a wide range of raw material sources, short production processes and many product variations, and are currently used in a wide range of skin-fitting applications such as medical protection, personal hygiene and intelligent temperature regulation. However, the polymer raw materials currently used in melt-blown nonwovens are mainly polymers such as polypropylene, polyethylene and polylactic acid, which contain multiple rigid molecular chain segments in their structure, resulting in brittle nonwovens that are not sufficiently tough. Therefore, how to improve the softness of melt-blown nonwovens so as to further develop their application in the field of skin-fitting products has become a major issue and research hotspot in the field of skin-fitting textiles.

This paper reviews the research progress on copolymer modification and blending modification of melt-blown polymer raw materials, summaries the influence of melt-blown nonwoven production processes on the flexibility of the materials and describes the forms of applications of melt-blown nonwovens in the field of flexible skin-fitting, providing references and new ideas for the flexibility improvement and skin-fitting application and development of melt-blown nonwovens.

The high melt flow index, narrow molecular weight distribution and low melt viscosity of the polymer raw materials used in the melt-blown process not only help the polymer melt to draw into fibers, but also improve the flexibility of the nonwoven materials by introducing other substances. A common method of improving the softness of polymers is therefore the copolymerization and blending of polymeric raw materials in the melt-blown process, and a great deal of work has been done by many researchers to improve the softness of polymers. Copolymer modification is to introduce the specific molecular chain segments into the main polymer macromolecule chain through a chemical reaction, so as to change the polymer molecular structure to improve the polymer molecular chain flexibility. In contrast, blending modification can be done by blending elastomers, small molecule oligomers or soft masterbatches to reduce the rigidity of the blends, which is a common physical modification method to improve the polymer flexibility, with the advantages of simple operation process and low production costs. In addition, the control of the forming process of melt-blown nonwovens can be easily regulated. The flexibility of the nonwoven material can be improved by making the resulting fibers finer in diameter, more porous and fluffier in structure by adjusting the process parameters such as the receiving distance, hot air pressure, hot air temperature and die head temperature. Therefore, the study of the influence of process parameters on the structure and properties of nonwovens can provide a reference for the further improvement of the softness and comfort of melt-blown nonwovens and the development of skin-fitting materials.

This paper presents a review of methods to improve the flexibility of melt-blown nonwovens and their skin-fitting applications. Based on this, it is found that adding flexible molecular chains to the macromolecular chains of polymer raw materials or melt blending them with flexible materials, or adjusting the parameters of the melt-blown nonwoven process, can effectively improve the flexibility of nonwovens. At the same time, there are several issues that need to be improved: (i) different types of polymer raw materials require different methods (chemical or physical) to improve material flexibility, and it should be considered that the method has the characteristics of simple operation, low cost and industrial mass production; (ii) it is also necessary to increase the diversity of functional applications of materials in improving the flexibility of melt-blown nonwovens, which is also a future melt-blown nonwovens research hotspot.

More and more scholars will pay attention to the research of melt-blown nonwovens for flexible skin-fitting application as the field of application of melt-blown nonwovens expands. This paper reviews the polymer modification methods, melt-blown nonwovens processes and applications of flexible skin-fitting nonwovens, with the aim of providing a reference for subsequent research on melt-blown nonwoven flexibility enhancement and its application in new skin-fitting products.

Key words:

melt-blown; nonwovens; toughness modification; copolymerization modification; blending modification; skin-fitting application

收稿日期:

2022-07-06;

修回日期:

2023-01-20

基金项目:

国家自然科学基金项目(52003306);河南省高等学校重点科研项目(23A540003);河南省重大科技专项项目(221100310500);先进纺织装备技术省部共建协同创新中心项目(2021-CYY-001);中原工学院自主创新应用研究项目(K2020YY002)

作者简介:

秦子轩(1996),男,硕士研究生,研究方向為新型非织造成型技术的研究。通信作者:张恒,副教授,zhangheng2699@zut.edu.cn。