聚乳酸烟用过滤嘴制备工艺及若干基础问题的研究

本论文适应聚乳酸烟用过滤嘴工业化的需要，针对烟用过滤嘴特殊的工艺和技术要求，进行了相关问题的基础研究。 在自制模型小纺丝机上进行了小试研究。研究了干燥条件、树脂水分含量、树脂规格、添加助剂、纺丝温度、纺丝速度，后处理等对聚乳酸可纺性、纤维性能的影响，确定了中试纺丝条件。在聚丙烯烟用丝束国产线上进行了中试研究，研究了纺丝速度，牵倍，牵伸温度，松弛热定型温度和时间对聚乳酸纤维力学性能、热学性能、粘接性能、开松性能、过滤性能的影响，进一步明确了树脂规格和纺丝条件，研发出适合聚乳酸香烟滤材的粘接剂，并且初步得到了吸阻和硬度符合接烟要求的过滤嘴棒。在卷烟厂进行了过滤嘴的香烟接装实验，结果表明聚乳酸香烟过滤嘴可以满足高速接烟的需要。 在实验室和卷烟厂分别进行了聚乳酸滤材吸附/过滤性能研究：1）在实验室，进行了聚乳酸纤维对烟气中典型的烟气成分的静态吸附实验；2）在卷烟厂，对接装聚乳酸香过滤嘴的香烟进行了烟气分析和品吸。结果表明聚乳酸烟用丝束对极性和非极性烟气成分气体有较高的吸附/吸收能力，但对烟碱的吸附却很少。因而聚乳酸过滤嘴的香烟可能有自己独特的吸味风格。聚乳酸香烟过滤嘴具有同二醋酸纤维素过滤嘴相近的过滤能力，可以有效的过滤烟气中的有害物质，过滤效果优于聚丙烯。 针对聚乳酸在熔体纺丝过程中热稳定性差这一关键问题，深入系统地研究了添加有聚碳化二亚胺聚乳酸的流变学行为、热学性能、热降解行为、力学性能、酶降解行为和稳定机制。实验结果表明在聚乳酸中添加抗水解稳定剂能显著提高聚乳酸的加工热稳定性，表现为经过熔体加工后，分子量较少下降，熔融指数增加不多，力学性能基本维持不变。改性的原因是聚碳化二亚胺在加工的过程中与残留的或加工过程中形成的乳酸和/或水分子反应，消除或减少了聚乳酸的水解，阻止了乳酸对聚乳酸水解的催化作用；与聚乳酸的端羟基或端羧基发生了化学反应，从而减少了通过端基“反咬”形成丙交酯而降解的可能性，甚至将端基偶联，使分子量增大。 通过高压静电纺丝制备具有不同三醋酸甘油酯（GTA）含量的聚乳酸超细纤维毡，场发射扫描电镜、示差扫描量热仪、水接触角和力学性能测试表明，随着GTA含量的增加，纤维之间趋于粘连，形成立体网状结构，纤维毡的断裂伸长率、回弹率、拉伸强度可分别达到200%、85%、4.24MPa，比不改性的聚乳酸超细纤维毡有显著地提高。当GTA含量在40%以下时，纤维粘毡表现出超疏水特性，表面表观水接触角约在130°左右，当GTA含量高于50%，水能迅速浸润和渗入纤维毡，表观水接触角为0°。

A quantitative HPLC method for determining lactide content using hydrolytic kinetics

A new method for quantitative analysis of lactide has been developed by applying chemical kinetics to a HPLC system. The most important advance is its practical approach to the quantification of analytes that are unstable in the HPLC mobile phase. In HPLC analysis, anhydrous mobile phases cannot separate lactide from impurities, and only mixtures of water and organic solvent can achieve effective separation. By selecting conditions for testing and studying the kinetics of lactide hydrolysis, extensive experiments revealed that lactide degradation can be treated as a pseudo-first-order reaction under the given HPLC conditions, and lactide content or purity can be quantitatively determined. This method is practical for measuring the purity of the intermediate lactide in polylactic acid (PLA) production and the lactide content in PLA.

An Amino Acid Substitution Matrix for Protein Conformation Identification

Amino acid substitution matrices play an essential role in protein sequence alignment, a fundamental task in bioinformatics. Most widely used matrices, such as PAM matrices derived from homologous sequences and BLOSUM matrices derived from aligned segments of PROSITE, did not integrate conformation information in their construction. There are a few structure-based matrices, which are derived from limited data of structure alignment. Using databases PDB_SELECT and DSSP, we create a database of sequence-conformation blocks which explicitly represent sequence-structure relationship. Members in a block are identical in conformation and are highly similar in sequence. From this block database, we derive a conformation-specific amino acid substitution matrix CBSM60. The matrix shows an improved performance in conformational segment search and homolog detection.

Preparation And Tribology Studies of Alkyl Carboxylic Acid Monolayer Films on Pei-Coated Glass Substrate

首次在涂敷PEI的玻璃表面上制备了癸酸及全氟癸酸的单分子层膜。研究了成膜机理及摩擦特性。结果表明。脱水剂DCCD促进了癸酸或全氟癸酸与PEI酞胺化的反应。导致两种羧酸在PEI表面产生了靠化学键（酞胺键）连接的稳定的单分子层膜,摩擦、磨损实验表明。单分子层有机膜的摩擦特性受膜的组成、表面能及有序性和堆积密度的重要影响。表面能越低,有序性和堆积密度越高。摩擦系数越低。与碳氢化合物相比。碳氟化合物形成的有序膜具有更高的强度和抗磨性能。

Preparation and Tribological Studies of Stearic Acid Self-Assembled Monolayers on Polymer-Coated Silicon Surface

We present a good alternative method to improve the tribological properties of polymer films by chemisorbing a long-chain monolayer on the functional polymer surface. Thus, a novel self-assembled monolayer is successfully prepared on a silicon substrate coated with amino-group-containing polyethyleneimine (PEI) by the chemical adsorption of stearic acid (STA) molecules. The formation and structure of the STA-PEI film are characterized by means of contact-angle measurement and ellipsometric thickness measurement, and of Fourier transformation infrared spectrometric and atomic force microscopic analyses. The micro- and macro-tribological properties of the STA-PEI film are investigated on an atomic force microscope (AFM) and a unidirectional tribometer, respectively. It has been found that the STA monolayer about 2.1-nm thick is produced on the PEI coating by the chemical reaction between the amino groups in the PEI and the carboxyl group in the STA molecules to form a covalent amide bond in the presence of N,N'-dicyclohexylcarbodiimide (DCCD) as a dehydrating regent. By introducing the STA monolayer, the hydrophilic PEI polymer surface becomes hydrophobic with a water contact angle to be about 105degrees. Study of the time dependence of the film formation shows that the adsorption of PEI is fast, whereas at least 24 h is needed to generate the saturated STA monolayer. Whereas the PEI coating has relatively high adhesion, friction, and poor anti-wear ability, the STA-PEI film possesses good adhesive resistance and high load-carrying capacity and anti-wear ability, which could be attributed to the chemical structure of the STA-PEI thin film. It is assumed that the hydrogen bonds between the molecules of the STA-PEI film act to stabilize the film and can be restored after breaking during sliding. Thus, the self-assembled STA-PEI thin film might find promising application in the lubrication of micro-electromechanical systems (MEMS).

Effects of Molecular Length, Ortientation and Amino Acid Mutation on Kinetics of Selectin/Ligand interactions

Receptor/ligand interactions are basic issues to cell adhesion, which are important to many physiological and pathological processes such as lymphocyte-mediated cytotoxicity, tumor metastasis and inflammatory reactionl. Selectin/carbohydrate ligand bindings have been found to mediate the fast rolling of leukocytes on activated endothelial monolayer. Kinetic rate and binding affinity constants are essential determinants of cell adhesion...