羧乙基化和碱预处理玉米芯渣制备纳米纤维素的研究

玉米芯提取木糖后剩余的残渣富含纤维素和木质素,采用羧乙基化反应和质量分数1%的NaOH溶液分别对玉米芯渣进行预处理,再经机械解离制备了纳米纤维素,最后经棒涂法制得纳米纤维素膜,并对预处理前后玉米芯渣、纳米纤维素及其膜的化学结构、组分含量、微观形貌、尺寸分布、水接触角和热稳定性进行了分析和表征。结果表明,羧乙基化预处理可增加玉米芯渣的羧基含量,同时脱除部分木质素,而碱预处理可脱除大部分木质素。经预处理后,玉米芯渣纤维尺寸明显降低、可及度增加。经机械解离后,羧乙基化预处理所得纳米纤维素的直径更小、分布更均匀,其经棒涂法所得膜也更加致密平滑,水接触角较大。另外,两种预处理方法均降低了所得纳米纤维素膜的热稳定性。

羧乙基化法制备纳米纤化纤维素

以阔叶木为原料,采用丙烯酰胺与氢氧化钠溶液对纤维素进行羧乙基化处理,引入羧乙基基团,然后在高压均质的条件下制备纳米纤化纤维素。研究丙烯酰胺用量、氢氧化钠用量、反应温度和反应时间对羧乙基含量的影响。单因素实验最优制备条件为丙烯酰胺用量1.89 g·g^(-1)绝干浆,氢氧化钠用量1.51 g·g^(-1)绝干浆,反应温度90℃,反应时间5h;对不同羧乙基含量的纳米纤化纤维素的性能进行表征,包括:长度、直径、长径比、聚合度和透过率。结果表明:羧乙基含量越高,尺寸和聚合度越小,透过率越高。当羧乙基含量1.89 mmol·g^(-1)时,纳米纤化纤维素的直径为20nm左右,长度为1.5μm左右,长径比为80左右,在800 nm处透过率为83.89%,聚合度为265。

壳聚糖丙酮酸衍生物的合成及吸湿保湿性能(英文)

以丙酮酸改性壳聚糖制备了N-(1-羧乙基)壳聚糖(CET),用1HNMR、电位滴定等方式对产物进行了表征。研究发现,丙酮酸与糖元比例、反应时间、pH和壳聚糖相对分子质量(Mw)对产物取代度(DS)影响较大,最佳丙酮酸与糖元比例、反应时间、pH分别为8∶1,8h,4.5。随壳聚糖Mw降低,DS增加。CET比壳聚糖的吸湿保湿明显增加,并呈现与HA类似的吸湿保湿性能。

壳聚糖衍生物用于市政废水阻垢

以壳聚糖(CTS)、丙烯酸(AA)为单体,以过硫酸铵(APS)为引发剂,在体积分数为2%的冰醋酸水溶液中共聚,制备了N-羧乙基化壳聚糖(CEC)。采用红外光谱、核磁共振光谱等对壳聚糖衍生物CEC进行了表征。以阻垢性能为评判标准,通过单因素实验筛选出CEC的最佳合成条件为:m(AA)∶m(CTS)=5.30∶3.00,反应温度为75℃,反应时间为4 h,引发剂APS用量为3%(以单体总质量为基准,下同)。考察了CEC用于二级市政废水中的阻垢性能,结果表明,在经过二级处理的市政废水中,CEC阻CaCO3垢性能优异,当CEC的加药量为30 mg/L时,对CaCO3的阻垢率可达92.93%,明显优于市售阻垢剂羟基乙叉二膦酸(HEDP)。通过SEM、XRD对CEC阻CaCO3机理进行了初步探究,结果表明,CEC对CaCO3的作用机理主要是晶格畸变作用。

Visible‐light photoredox‐catalyzed carboxylation of benzyl halides with CO_(2):Mild and transition‐metal‐free

The visible‐light photoredox‐catalyzed carboxylation of benzyl chlorides and bromides with CO_(2) has been reported.With inexpensive organic dyes as photocatalysts and amines as electron donors,this carboxylation proceeds well in the absence of sensitive organometallic reagents,transition metal catalysts,or metallic reductants.A wide range of commercially available and inexpensive benzyl halides undergo such carboxylation to give valuable aryl acetic acids,including several pharmaceutical molecules and drug precursors,in moderate to high yields.Moreover,this reaction features mild reaction conditions(one atmospheric pressure of CO_(2) and room temperature),broad substrate scope,good functional group tolerance,easy scalability,and low catalyst loading,thus providing an efficient approach for the assembly of aryl acetic acids.

Preparation and characterization of ferromagnetic fluids modified by carboxyl PEG

To prepare and characterize the ferromagnetic fluid of Fe304 modified by carboxyl PEG （FF/carboxyl PEG） for hyperthermia of tumor, the magnetic nanoparticles （NPs） of Fe304 were prepared by chemical co-precipitation method, and then modified with carboxyl PEG. The iron content of FFs was determined by spectrophotometric method using o-phenanthroline. The stability of FF/carboxyl PEG was assessed by the sedimentation method. FF/carboxyl PEG was characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, infrared spectrometry （IR） and vibrating sample magnetometer （VSM）. Heating effect of FF/carboxyl PEG was measured in an alternating magnetic field in vitro. The stability of FF/carboxyl PEG was much better than that of unmodified ferromagnetic fluid. FF/carboxyl PEG was proved to be composed of Fe304 by both XRD and IR. TEM showed that the ferromagnetic particles were well-dispersed. The average particle size was calculated as 5 nm by XRD. The saturation magnetization and residual magnetization of FF/carboxyl PEG were 47.01 and 3.41 emu/g, respectively. The coercive force was 6.70e. The specific absorption rate （SAR） of the FF/carboxyl PEG was 63.0 W/g[Fe]. The FF/carboxyl PEG shows the promise for hyperthermia of tumor.