服用纺织品是环境和人体间的围护结构物,除用来控制人体与环境之间的能量(热能、冲击能、光能、电能、电离辐照能等)和物质(空气、水蒸气、雨水、汗水、尘埃等)的透通和传递外,还应对环境存在的微生物,尤其是致病微生物进行阻隔和抑制,防止传染疾病侵袭人体皮肤;并要对皮肤和纤维上附着的微生物进行适度控制,既要抑制致病微生物的生长和增殖,又要避免对常驻菌和过路菌的过分“伤害”。从微生物组学的角度看,人体是由人类基因组与共生微生物基因共同构建的超级生物体,二者相互依存,共同维持人体健康稳态。有研究[1]将基因和微生物对人体健康的共同作用生动描述为“血脉”与“菌脉”并存的关系,强调了维持体表微生物生态平衡对于人体健康至关重要。因此,现代抗菌纺织品的设计理念正在发生深刻变革。其核心目标不再是广谱、高效地消灭所有微生物,而是实现“靶向化”和“适度化”的精准控制。这意味着,理想的抗菌纺织品应能有效抑制或阻隔环境中的致病微生物,防止其侵袭皮肤引发疾病;同时,又要避免对皮肤上庞大而有益的常驻菌群造成过度伤害,保护“菌脉”的健康与稳定。
随着生活水平的提升,消费者对纺织品抗菌、防臭等健康功能的需求日益增长。为响应这一趋势,纺织科技界对抗菌防臭技术的研发投入了巨大热情,催生了一系列创新技术与前瞻性见解。基于已有研究成果,本文重点剖析基于超临界流体技术和电子束辐照交联技术的抗菌剂高效固着新方法,以及通过构建纤维表面纳米结构以物理方式调控微生物行为的新策略,旨在通过多角度的分析与讨论,为我国抗菌防臭纺织品技术的未来发展理清思路、探明方向。
1 抗菌剂在纤维浅层的高效环保固着
1.1 共混纺丝
将可耐受纺丝温度的抗菌剂(例如银/铜/锌或其金属盐、稀土等无机抗菌剂,TiO2光触媒粉体,及一部分耐温性好的有机抗菌剂及高分子抗菌剂)与成纤高聚物共混纺丝,制成抗菌纤维后通过与普通纺织纤维混纺、交织等方法集成到织物中,使抗菌剂发挥抗菌防臭作用。根据抗菌纺织品安全性卫生要求[2],抗菌纺织品的抗菌物质应为非溶出性或微溶出性的抗菌剂,最终制品的抑菌圈直径应小于5 mm,故抗菌纤维多采用不易溶出的抗菌剂,且基本上只有存在于纤维表面的抗菌物质才能起抗菌作用。通过调整纺丝工艺可使抗菌剂倾向于聚集到纤维表面,但发挥抗菌作用的抗菌剂也仅是投料量中的一小部分,处于纤维内部的抗菌剂,易成为内部缺陷,降低纤维的强度和可纺性。当需要增强抗菌效果增加抗菌剂用量时,负面影响更加突出。采用皮芯复合纺丝方法可仅在纤维皮层施加抗菌剂,以改善上述状态,但皮层厚度不可能很薄,仍存在抗菌剂浪费及纤维性能劣化等问题。还有研究者利用银镜反应对长丝镀银,经微量电离/氧化生成银离子,起到抗菌作用,但银的氧化会导致颜色变化,并因持续氧化而脱落失效。
1.2 织物后整理
在织物染整加工过程中,在定形机前轧液槽中施加季铵盐、卤氨、胍类有机抗菌剂或高分子抗菌剂,在某些搭配方式下(例如蛋白质纤维与卤氨)可自然得到可靠的共价键结合,获得持久的抗菌效果;某些搭配(例如纤维素纤维与季铵盐)需将季铵盐改性为有机硅季铵盐,通过有机硅水解生成高活性的硅醇基(—Si(OH)3),再由硅醇基与纤维素表面的羟基发生脱水缩合反应,形成稳定的Si—O—C共价键。而很多搭配方式(例如聚酯纤维、纤维素纤维与这些有机抗菌剂)不能直接形成化学连接,需对纤维进行改性预处理,或借助交联剂实现键合,但交联剂的使用会导致织物手感变硬、易于脱落,且残液残留抗菌剂成分易破坏污水处理系统微生物群落平衡。
采用类似分散染料染涤纶的方式,在涤纶溶胀条件下将各种抗菌剂渗透并锚定于纤维表面浅层结构,在降温后随着纤维收缩,可将抗菌剂分子或微粒固着于纤维表面(有足够的固着牢度);但在常规染整设备的温度和压力条件下,可溶胀到适合抗菌剂植入的纤维品种有限,抗菌剂在纤维表面固着数量和牢度也有限,难以实现有效的抗菌效果,故需采用超临界流体对纤维实施充分的溶胀,并携带抗菌剂进入纤维的浅层表面。
为突破上述瓶颈,采用超临界流体技术将抗菌剂固着于纤维浅层表面成为一项极具前景的新技术。该技术借鉴了超临界CO2无水染色技术的成熟原理。
1.3 超临界CO2处理
超临界流体是温度和压力处于临界点以上的流体。以最常用的CO2而言,在31.1 ℃、7.38 MPa以上即达到超临界状态。处于超临界状态的CO2具有低黏度、低表面张力和高渗透特性,可溶胀和溶解大多数高分子材料,并可携带小分子或微纳尺度颗粒物进入所溶胀的物质。绿色环保的超临界染色技术即为典型范例,在超临界状态下该技术使染料渗入发生溶胀的纤维内,经降温释压后染料即充分固着在纤维上。同时,在恢复常压后超临界流体可循环利用,剩余的染料可以回收,纤维制品可自然干燥。此外,超临界流体本身也是一种有效的杀菌手段。
采用超临界技术可对高分子纤维材料进行各种抗菌剂的固着加工。南京禾素时代抗菌材料科技集团有限公司采用超临界技术将其生物基抗菌剂聚3-羟基丁酸酯低聚物(OPHB)固着于各类纤维上,该技术处理后的棉纤维即使再经过丝光处理,仍保持突出的抗菌效果;对羊绒制品施加OPHB处理后,手感无变化[3],显示出优异的整体效果,但超临界设备的制造成本高于一般常压设备,以超临界CO2为例,在7.38 MPa的高压下,尚难实现连续生产,只能采取间歇式生产方式进行加工。
采用超临界技术可将抗菌剂固着于天然纤维和化学纤维的浅层表面,既节省抗菌物质也不影响纤维力学性能;且因抗菌剂的施加量仅为纤维质量的千分之几,还不影响染色性能;不需要添加交联剂即可牢固地在各种纤维表面植入抗菌剂,还不影响纺织品的手感,因此,该项技术解决了传统抗菌纤维和抗菌织物加工中存在的主要问题,且制成的抗菌纤维具有良好的后加工性能,是一项技术成熟、实用性强的高水平新技术。
2 电子束辐照接枝抗菌剂技术
直线扫描式或帘式电子加速器作为电离辐射源,特别适合高分子材料的辐照改性加工,且与γ射线源相比,辐照均匀性更好、安全性更强。电子加速器发射的高能电子作用于纺织纤维的大分子主链或侧基,会断链并产生高活性的自由基,引发辐照降解效应(导致高分子物聚合度下降,例如粘胶纤维厂采用辐照技术代替原“老成”工序降低纤维素聚合度使之适合工艺要求)、辐照交联效应(使不同大分子链上的自由基相互结合,或同一分子链上的自由基发生反应,形成三维网络结构。例如聚烯烃弹性纤维(XLA)就是依靠辐照交联形成硬链段来实现弹性变形和回复能力)和辐照接枝效应(纤维大分子上产生的自由基与功能性单体实现接枝聚合,形成各种功能。例如对丝绸辐射接枝丙烯腈提高弹性、对聚酯(PET)辐射接枝含氟单体形成拒水效果)。显然,通过辐照接枝方法可将抗菌剂接枝到纺织纤维,且其加工方式均具有高效、安全、节能、无污染的优点;采用电子加速器作为电离辐射源,比γ源辐射均匀可控、管理运行简单、安全性更佳。
2.1 电子束辐照接枝加工方式
电子束辐照接枝抗菌剂有共辐照和预辐照2种方式。前者是将纤维材料与欲接枝的抗菌剂共同放入高能射线的辐照区域,让纤维材料出现自由基时即与功能性单体发生接枝反应,加工简单,但存在功能性单体发生均聚的可能性;后者则是先单独对纤维材料进行辐照加工,在产生自由基后投入到含有功能性单体的工作介质中,使辐照产生的自由基与功能性单体发生接枝反应,该操作需要有2个加工步骤,但避免了功能性单体均聚的可能性。
2.2 辐照工艺对抗菌性能的影响
在辐照剂量的运用上,需兼顾辐照接枝效应和辐照降解效应的平衡。对于辐照降解型纤维材料(例如纤维素纤维),如果辐照剂量过大、或辐照环境有利于辐照降解,会导致比较明显的降强,例如棉织物在33 kGy辐照剂量下接枝卤氨类抗菌剂,采用预辐照工艺使棉织物强度降低29.8%,采用共辐照工艺时因单体对棉纤维起到保护作用,强度损失降低到19.2%[6];周莉等[7]的研究表明在获得较好抗菌效果的同时,织物强度保留率也达到80%左右,可满足一般使用要求。相比之下,涤纶因其不属于辐照降解型高分子材料,故在50 kGy辐照剂量下接枝丙烯酸二甲氨基乙酯(DMAEA)、并用碘甲烷对DMAEA进行季铵化,使织物对大肠埃希菌的抑菌率达到75%以上,而强度仅下降3.8%[8];维纶也有类似涤纶的辐照耐受性,辐照剂量从1 kGy逐步增至25 kGy,样品强力均无明显改变[9]。
除电子束外,各种不同频率的电磁波(太赫兹波、微波、红外线、可见光、紫外线、γ射线)据其强度不同,也可能具有一定程度的杀菌消毒效果,但有显著的制约因素,即辐射能量的穿透深度。一般认为,太赫兹波、红外线、可见光、紫外线对被照射对象实体的穿透深度最高约数毫米,且这些电磁波的能量较低,除紫外线可引发核酸和细胞壁、细胞膜的破坏外,其它电磁波只有微弱的热效应;微波、γ射线和电子束的渗透深度可达数厘米,对薄片型纺织材料和制品的改性加工而言是合适的,但对较大堆集体积的纺织品集合体的消毒而言,深部能量渗入不够,而表层局部易因辐射能量过度而受损;且对于高分子材料而言,即使是高强度的电离辐射,也不会产生感生放射性,故这些电磁波或电子束照射纤维材料后,即使有消毒杀菌作用,也不存在持续的抗菌效果。
3 材料表面纳米结构的抗菌新技术
抗菌纺织品的理想状态是对需要抑制的致病微生物具有靶向性的抗菌能力、且对一般微生物减少杀伤力,以免对共生菌、过路菌造成误伤,但是,采用化学或生物学原理进行杀菌的抗菌纺织品均无法达到上述理想状态。如何建立更先进、更具生态智慧的“接触抗菌”或“结构抗菌”体系的难度不小,但可以从微生物对被沾染物的定殖过程分析,来建立新的抗菌思路。
3.1 纳米抗菌结构的设计与分析
微生物从环境或人体皮肤接触沾染于纺织纤维,到定殖形成生物膜的过程中,初次接触时具有易受纤维材质和微纳表面干扰的特点,且易脱落和去除;一旦完成附着,就会增殖形成微菌落并逐渐扩大在纤维上的覆盖面积,同时分泌由多糖、蛋白质、核酸和脂质组成的黏性基质(即胞外聚合物)如同“生物胶水”将细菌牢固锚定在纤维表面,成为长期存活和传播的主要形式[12],如长期困扰海洋航运和渔业生产的海洋微生物及藤壶、海藻等生物污染船体、缆绳、渔网的海洋污染问题。在医用纺织品上,VARSHNEY 等[13]指出,80%以上的感染源于致病菌的生物膜,且生物膜内的微生物对洗涤、消毒乃至抗生素的抵抗力,较之初始固着状态的微生物显著上升。即使受到消毒处理或在营养匮乏状态下,生物膜内的病菌会处于低代谢活性的“存活但不可培养”(VBNC)状态[14],许多毒力基因并未完全“沉默”,编码毒素、黏附素、侵袭素等关键致病因子的基因仍存在且可恢复[15-16]。
由此可见,抗菌纺织品应该在致病微生物尚未完成定殖且形成生物膜前,预先通过材质选择和纤维表面微纳结构的设计,来破坏微生物在纤维表面的固着。因为初始接触是基于微生物与纤维表面之间的范德华力、静电力和疏水相互作用发生的,微生物的细胞膜、鞭毛及菌毛等附肢结构形态、表面的疏水性和电荷,与纤维表面的物理化学性质的搭配状态,决定了微生物在纤维上的初始定着量和结合牢度。例如, 聚酯织物对金黄色葡萄球菌(SA)和铜绿假单胞菌(PAE)的初始定着量分别为3.5%和3.0%;聚酰胺织物对SA和PAE的初始定着量分别为2.1%和2.4%,而棉织物对SA和PAE的结合率分别为1.8%和1.6%[17],可见,在没有形成稳固的生物膜前,聚酯纤维制品更容易接收和固着致病菌,而棉纤维容易将所接触的致病菌洗脱。这是用来调整微生物与纤维定殖状态的一种方法,该方法具有一定的靶向性,并突破当前认为亲水性好的棉织物更易接纳更多细菌的思维定势。
更有靶向抗菌效果的是在纤维表面构建柱状、锥状、片状等密集的纳米尺度结构阵列,因为附着其上的微米尺度(数微米~数十微米)细菌受若干纳米尺度支点的托举,会因为支点尺度极小,导致在微生物自重、纳米尺度阵列缝隙形成的毛细力作用下产生极大压强,将微生物细胞膜穿刺或撕裂,以及细菌运动[18]导致细胞壁在2个纳米支点之间发生撕扯,在力学作用下使细胞死亡;且因为不同菌种的尺度和胞壁厚度及强度差异,造成纤维表面的纳米结构对不同细菌具有不同的杀伤力,这就为构建纤维的靶向性抗菌功能提出了探索途径。
3.2 仿生纳米结构作用机制
基于表面纳米结构的抗菌思路源于仿生学。例如:蝉翼表面存在基部直径为100 nm、端部直径为60 nm、中心距为170 nm、高度为200 nm左右的纳米柱集合体,能在60 min内杀死所有附着的PAE细胞[19]。类似地,蝴蝶、蜻蜓等昆虫翅膀;荷叶、芋头等植物叶片;壁虎、鲨鱼等动物皮肤表面,均有类似效果,但对不同菌种有不同的抗菌效果。研究者基于仿生学原理,采用激光刻蚀、软光刻、等离子体刻蚀、纳米模板等手段进行表面纳米结构构建方法的探索,通过激光刻蚀和水热处理在钛合金上形成直径20 nm的针状定向结构,抗细菌黏附力达66.6%、抗菌速率达1.23×107 CFU/(cm2·min)[20];用碳纳米管建立的阵列表面可在60 min内杀灭约80%大肠埃希菌,电镜照片示出碳纳米管端部对细胞膜造成损伤并使之失活[21]。模拟蜻蜓翅膀,采用反应性离子刻蚀法制得的直径为80 nm、高度为500 nm的亲水性黑硅纳米结构阵列表面,对革兰阴性菌和革兰阳性菌以及芽孢菌都分别有不同强度的杀菌能力,3 h内的杀伤率可达1.4×105~4.5×105 个/cm2 [22]之间,杀菌效果也显示出靶向性倾向。
显然,要在纺织纤维和纺织品上构建纳米阵列结构,并理清纳米阵列结构特征对不同微生物的靶向抗菌效果难度较大,但研究基于材料表面纳米结构的抗菌新技术,有重大的科学意义,并相信通过跨界联合,持之以恒,终究会解决现有抗菌方法存在的缺乏靶向性的问题。
4 结束语
超临界CO2技术作为纺织抗菌加工的革新方向,凭借流体优异的渗透与携载能力,可将抗菌剂分子或纳米颗粒高效输送至纤维浅层结构,实现抗菌功能的绿色赋予,其高效、环保特性已成为替代传统化学抗菌工艺的核心优势。
电子束辐照技术在纺织抗菌领域的应用已展现显著潜力,不仅能赋予制品长效抗菌性能,更在协同实现辐射降解(净化加工环境)与辐射接枝(强化抗菌剂结合牢度)方面积累关键经验,未来需进一步拓展其在多品类纤维(如再生纤维素纤维、高性能合成纤维)中的适配性研究。太赫兹波、微波、红外、可见光、紫外线及γ射线等电磁辐射技术,需针对不同纤维材质与加工目标,重点突破“辐射深度精准调控”技术瓶颈,开发智能化辐射参数控制系统,以满足多样化纺织抗菌加工需求。
基于仿生学原理构建的柱状、锥状、片状纳米纤维阵列,为实现靶向抗菌与适度抗菌提供了全新技术路径,有望解决传统化学或生物杀菌方法“无差别”抗菌的痛点。当前该领域虽处于纳米结构阵列制备技术优化、阵列结构与致病微生物种类/结构关联性研究的初步阶段,但未来可通过跨学科合作(纺织科学与微生物学、纳米科学深度融合),重点攻关以下方向:一是开发低成本、规模化的仿生纳米纤维结构阵列制备工艺;二是建立“阵列结构参数-抗菌靶向性-微生物作用机制”的关联模型;三是探索仿生纳米阵列与其它抗菌技术的协同应用模式,推动纺织抗菌技术向高效化、精准化、绿色化方向升级,为医疗防护、卫生保健、户外保护等领域纺织品提供更优质的抗菌解决方案。
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