摘要
木质素由于其特殊结构而具有抗紫外线、抗菌等特性,在紫外防护领域具有广阔的应用前景。为了更大程度地实现木质素的广泛利用,木质素纳米颗粒的研究一定程度上解决了木质素结构复杂、不均一以及颜色较深等问题,同时其抗紫外线能力进一步增强。本文详细介绍了木质素的紫外线防护功能、木质素纳米颗粒的制备及其在紫外防护领域的应用,为木质素在紫外屏蔽领域的资源化利用提供参考。
太阳光中含有丰富的紫外线,尽管经过大气层后仅有少部分到达地面,但仍然会对人类的生活环境造成危害。近年来,随着臭氧层的破坏,抵达地球表面的紫外线辐射增加,紫外线辐射对生态环境的影响日益加
木质素是自然界中储量仅次于纤维素的大分子聚合物,也是自然界储量最多的可再生多酚类化合物。由于其特殊结构,木质素具有抗紫外线、抗菌等优异性能,是一种广谱的防晒
目前,紫外线屏蔽剂可以分为无机紫外线屏蔽剂和有机紫外线屏蔽剂。其中,无机紫外线屏蔽剂又称物理屏蔽剂,即通过将金属氧化物、陶瓷粉等与纤维织物结合在一起,提高其对紫外线的折射和反射能力,从而达到对紫外线的防护效果。常见的无机紫外线屏蔽剂主要有TiO2、ZnO纳米颗粒
木质素是天然高分子化合物,作为植物细胞壁的重要组分之一,广泛存在于维管束植物中,是仅次于纤维素的第二大生物质资源,被誉为21世纪可被人类利用的最丰富的绿色资源之

图1 木质素的紫外防护特
Fig. 1 UV protection properties of ligni
不同分离途径获取的木质素结构不同,主要分为作为结构表征样品的天然木质素和作为工业和预处理过程副产物的工业木质素。天然木质素中应用最广泛的是磨木木质素(MWL)和纤维素酶解木质素(CEL),由于分离成本较高而不适合大规模开发利用;工业木质素主要来源于制浆和生物乙醇精炼过程。在制浆造纸和生物乙醇精炼工业中,为了充分利用纤维素和半纤维素,木质素作为脱除后的副产物通常被低值燃烧甚至丢弃。目前,木质素相关研究主要集中于工业木质素的开发与利用。工业木质素年产量约5 000万t,超过95%的工业木质素仅作为燃料用于发电或以废液形式排入江河湖泊,利用率低且环境污染负荷
随着纳米技术的发展,木质素纳米颗粒(LNP)的制备及应用备受关注。LNP比表面积大、表面活性高且形态大小容易控制,是提高木质素应用性能的一种重要途径,在碳材料、分散剂、生物黏合剂及紫外防护产品等方面具有广阔的应用前
LNP是根据木质素自身的亲/疏水特性、氢键以及π-π相互作用制备得到的粒径和形状均匀的球形纳米颗粒。制备过程中,随着亲水基团与水分子相互作用、疏水骨架与有机溶剂相互作用,木质素会趋于自组装成球状颗粒。同时,可以利用LNP的表面修饰进一步拓展其多样化应
相较于木质素,LNP除了具有比表面积大、粒径较小等一般纳米粒子的特性,还克服了木质素分子结构复杂、分子结构无规律等问题,同时也可以增加表面羟基的含量,改善木质素与基质之间的共混性能,使其在聚合物中分布均匀,提高抗紫外线、抗氧化以及抗菌等能
天然木质素是白度约为70%的淡乳白色高分子化合物,但在工业加工提取的过程中,大量发色官能团(如共轭羰基、甲氧基、苯环、醌型结构等)的引入及木质素分子的高密度聚集使得木质素呈现较深的颜色,这无疑会限制木质素在防晒霜、水凝胶等领域的应用和推广。目前,为了获得浅色木质素,通常采用不同的溶剂破坏木质素中的发色基团,但往往也会降低其紫外线屏蔽性能;或者利用低共熔溶剂法等方法获得低聚合度的木质
改性木质素,尤其是LNP凭借其良好的分散性和高比表面积有效增强了聚合物基质的相容性。将LNP和聚甲基丙烯酸甲

图2 TLNP/CLMP制备复合膜的紫外吸收特
Fig. 2 UV absorption characteristics of composite films prepared by TLNP/CLM
作为一种亲水性的三维网络结构聚合物,水凝胶具有良好的溶胀性、黏度和机械强度,在生物医学、环境保护等领域有广泛的应用。由于丰富的酚羟基和苯基丙烷单元的存在,LNP具有强大的紫外吸收能力,在功能化材料水凝胶生产中有广泛的应用前
随着紫外线辐射的加强,防晒霜已经成为人们外出的必需品之

图3 碱木质素脱甲基化后接枝二苯甲
Fig. 3 Grafting of benzophenone onto alkali lignin after demethylatio

图4 LNP制备防晒
Fig. 4 Preparation of sunscreen with LN
LNP的使用不仅可以淡化木质素原有颜色,还可以强化紫外线吸收和抗氧化性能,不仅在防晒霜中,在织物和涂料领域也有一定的应用。研究表明,以松木为原料,利用溶剂法和自组装法制备木质素纳米胶体球,加入清漆后可以使其具有更好的抗紫外线和抗氧化性

图5 LNP/CS复合材料合成路线及应
Fig. 5 Synthesis route and application of LNP/CS composite material
木质素含量丰富,具有成本效益低、生物相容性好及可生物降解等优点。同时,木质素还具有抗氧化、抗菌、抗癌和紫外线防护等多种药理活性。近年来,木质素已成为一种流行的生物聚合物,在生物医药领域的稳定化应用得到了广泛研
为了贯彻绿色环保、可持续发展的理念,实现“碳中和”“碳达峰”等号召,利用可再生能源取代传统化石能源进行生产生活已经成为了全社会高质量发展的趋势。通过物理、化学以及生物法制备的木质素纳米颗粒(LNP)能够克服木质素结构复杂、分散性差等问题,在多功能复合膜、水凝胶、防晒霜以及生物医药等领域已经有了初步的研究和应用。同时,也是制备浅色木质素的重要方向。然而,受限于成本、制备方法等问题,LNP的制备仍然处于起步阶段。因此,开发绿色经济、安全高效的LNP制备方法,推动LNP在紫外防护领域更广泛地应用,有利于木质素资源的开发,具有重要的经济效益和社会意义。
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