棉织物可控接枝核苷酸/氨基酸梯度聚合物的成炭行为和阻燃机理

Phosphorus-containing flame retardants are mainly employed in flame retardant modification to solve the problem of flammability of cotton fabrics. Physiological toxicity has been found in some of synthesized phosphorus-containing flame retardants. Moreover, excessive formaldehyde is released from durable phosphorus-containing flame retardants. Recently, bio-based flame retardants provide a new method for green flame retardant modification. DNA is a bio-based macromolecular intumescent flame retardant used for modification of cotton fabric via layer-by-layer self-assembly. However, the natural connection between nucleotides in a DNA strand and physical adsorption of DNA onto fiber surface result in poor durability and efficiency of flame retardancy. In this research, poor durability of flame retardant properties is to be avoided via RAFT controlled graft polymerization of N-acryloyl-ribonucleotide monomer towards cotton fabrics. The decreased steric hindrance of N-acryloyl-ribonucleotide monomer and formation of synergistic gradient polymer are to be achieved by simultaneous addition of N-acryloyl-amino acid monomer. Subsequently, flame retardant protective multilayers are to be formed on fiber surface and inside the fiber upon swelling cotton fibers to solve the problem of poor efficiency of flame retardancy. The relationship between the chemical structure and space conformation of grafted gradient polymer and the structure and morphology of hierarchically porous char is to be analyzed to clarify the behavior of char formation of gradient polymer. Moreover, the influence of distribution of gradient polymer on the surface of hierarchical fractal fibrillar cellulose on flame retardant properties is to be discussed, illustrating flame retardant mechanism. The research will provide a scientific theoretical foundation for applicable graft retardant techniques.

棉织物大多采用含磷阻燃剂进行阻燃改性以解决易燃性问题，但部分合成含磷阻燃剂具有潜在生理毒性，而耐水洗含磷阻燃剂大多甲醛含量超标。近年来发现的生物基阻燃剂为棉织物绿色阻燃提供了新途径。其中，DNA作为大分子膨胀型阻燃剂经层层自组装对棉织物改性，但其固有的核苷酸堆砌方式和对纤维表面的物理吸附导致其耐久性差、阻燃效率低。本课题拟采用RAFT可控接枝N-丙烯酰基核糖核苷酸单体的方法，解决阻燃耐久性差的问题。同时引入N-丙烯酰基氨基酸单体，既可降低核苷酸单体空间位阻又堆砌成协效阻燃的梯度聚合物，进而通过溶胀棉纤维，在其表面和内部形成多层阻燃保护层，以解决阻燃效率低的问题。通过分析梯度聚合物的化学结构和空间构象与燃烧时形成多层次炭的结构和形态间的关系，明确其成炭行为；分析棉纤维溶胀状态下梯度聚合物在多级原纤体表面的分布对阻燃性能的影响规律，确定其阻燃机理，为后续易规模化推广的接枝阻燃技术提供理论参考。

棉织物大多采用含磷阻燃剂进行阻燃改性以解决易燃性问题，但部分合成含磷阻燃剂具有潜在生理毒性，而耐水洗含磷阻燃剂大多甲醛含量超标。DNA作为大分子膨胀型阻燃剂经层层自组装对棉织物改性，但其固有的核苷酸堆砌方式和对纤维表面的物理吸附导致其耐久性差、阻燃效率低。本项目成功合成烯丙基溴改性磷酸腺苷单体、甲基丙烯酸缩水甘油酯（GMA）改性一磷酸腺苷单体（AMP-m-GMA）、GMA改性二磷酸腺苷单体（ADP-m-GMA）、GMA改性三磷酸腺苷单体（ATP-m-GMA）、烯丙基半胱氨酸单体、纤维素基二硫代酸酯类RAFT链转移剂，通过光接枝和RAFT接枝制备了生态阻燃棉织物。在磷酸腺苷单体中加入质量分数10%半胱氨酸单体，或将双键与磷酸腺苷母体间的碳链长度增加至C6，都可有效降低磷酸腺苷单体的空间位阻，提高了接枝率，形成的梯度接枝聚合物将棉织物的续燃时间和阴燃时间降低至0s。AMP-m-GMA/ADP-m-GMA/ATP-m-GMA质量比为0.2/1/0.8时，梯度接枝聚合物燃烧时形成球形膨胀炭结构，残炭的石墨化程度提高，使棉织物无续燃和阴燃时间且损毁长度减至9.8cm，极限氧指数约为28.41%，满足国标要求。不同溶胀程度下梯度聚合物在多级原纤体表面的分布对阴燃时间的缩短更为有效。RAFT接枝聚合物和光接枝聚合物在不同pH值下空间构象的变化对阻燃性能影响甚小。受热时接枝聚合物先于纤维素在较低温度下进行分解，产生不燃性气体，逸出时受到炭层的束缚导致，形成膨胀炭层。厚炭层对热传导和热辐射形成阻隔，较好地阻止热和氧的传递，实现良好的阻燃效果。本项目研究成果为后续易规模化推广的接枝阻燃技术提供了理论参考。