天然大分子材料化學(xué)課件

1、天然大分子材料化學(xué)天然大分子材料化學(xué)n纖維素n淀粉n天然膠n其他天然大分子天然大分子材料化學(xué)纖維素（Cellulose）n纖維素是資源豐富的天然高分子化合物(830 million tons)，主要來(lái)源于棉花和木材，除了棉花中的長(zhǎng)纖維可以直接紡制成織物外，棉花短纖維和木材中纖維素必須經(jīng)過(guò)適當(dāng)?shù)幕瘜W(xué)反應(yīng)后才能形成有用之物n由其結(jié)構(gòu)式可見(jiàn)，纖維素的每個(gè)結(jié)構(gòu)單元含有三個(gè)羥基，故纖維素有很強(qiáng)的氫鍵，結(jié)晶度(60-80%)也很高，所以天然纖維素加熱直至分解也不熔融，難于加工。但可以利用這些羥基的化學(xué)反應(yīng)，如酯化、醚化等，破壞氫鍵，改變其性能天然大分子材料化學(xué)纖維素的溶解（粘膠纖維）n纖維素通過(guò)化學(xué)反應(yīng)變

2、成可溶性黃原酸衍生物，然后紡絲或成膜n2，3和6位上的羥基都有可能起黃原酸化反應(yīng)，實(shí)際生產(chǎn)中黃原酸化程度為每個(gè)重復(fù)單元大約0.5個(gè)黃原酸基團(tuán)，這可足以形成纖維素溶液天然大分子材料化學(xué)纖維素的降解（degradation）n氧降解（Oxidative degradation）n堿降解（Alkaline degradation）n酸水解（Acid hydrolysis）天然大分子材料化學(xué)Oxidative degradation天然大分子材料化學(xué)Alkaline degradationnUnzipping reaction at the reducing end group leads to a

3、weight loss, but not a loss in DP, continues until it is stopped by an irreversible stabilization reactionnchain scissionEnolization烯醇化天然大分子材料化學(xué)nThe generally accepted mechanism for alkali catalyzed cleavage of the glycosidic linkages in nonoxidized cellulose has been derived mainly from studies of

4、model compounds, I.e. various -D-glucoopyranosides. The proposed mechanism is shown below天然大分子材料化學(xué)Acid hydrolysisnA slow scission of the glycosidic linkage is the rate-determining stepnAttack of the linkages occurs primarily in the disordered regionsnThe decrease in DP is limited (length of cellulos

5、e crystallite)天然大分子材料化學(xué)Cellulose derivativesnCellulose esternCellulose ethersnCyanoethyl（氰乙基） cellulosenDeoxy （脫氧） cellulosenCellulose carbamates（氨基甲酸酯）nCellulose xanthate（黃酸鹽）nCellulose sulfate esters天然大分子材料化學(xué)Cellulose estersnInorganic esters(cellulose nitrates, cellulose phosphate)nEsters of organ

6、ic acidsCellulose Triacetate（三乙酸纖維素）Secondary cellulose acetate （二乙酸纖維素）Cellulose monoacetates（乙酸纖維素）Cellulose butyrate （丁酸纖維素）Mixed cellulose esters天然大分子材料化學(xué)纖維素的酯化（esterification）n纖維素的酯化產(chǎn)物有醋酸纖維、醋酸-丙酸纖維、醋酸-丁酸纖維和硝化纖維等n醋酸纖維為在強(qiáng)酸催化劑（如硫酸）存在下，在醋酸和醋酐混合液中進(jìn)行乙?；姆磻?yīng)，如下所示n控制適當(dāng)?shù)臈l件，可得到三醋酸纖維素。部分乙酰化纖維素是將三醋酸纖維素部分水解間

7、接制成n酯化纖維素可以作為熱塑性塑料，能用模壓、擠出等方法加工，醋酸纖維素可用作電影膠片、涂料、塑料制品，但用量最大的是作人造纖維（又稱人造絲）天然大分子材料化學(xué)Cellulose ethersnMethyl cellulose（MC，甲基纖維素）nEthyl cellulose（EC，乙基纖維素）nCarboxymethyl cellulose（CMC，羧甲基纖維素）nHydroxyethyl cellulose（HEC，羥乙基纖維素）nHydroxypropyl cellulose（HPC，羥丙基纖維素）nCarboxymethyl hydroxyethyl cellulose（CMHEC

8、）nHydroxy ethyl methylcellulose（HEMC）nHydroxy ethyl ethyl cellulose（HEEC）nHydroxy propyl methyl cellulose（HPMC）nHydroxy butyl methyl cellulose（HBMC）天然大分子材料化學(xué)纖維素的醚化（etherification）n可由纖維素與氯代烷在氫氧化鈉作用下，反應(yīng)制得纖維素醚化產(chǎn)物，其中甲基和乙基纖維素最為重要，其反應(yīng)式如下n乙基纖維素具有耐化學(xué)試劑、耐寒、不易燃，對(duì)光與熱較穩(wěn)定以及能溶于廉價(jià)溶劑等優(yōu)點(diǎn)，故可廣泛地用于涂料、清漆、乳化劑、上漿劑、上光劑和粘合劑

9、等nCMCBy-product天然大分子材料化學(xué)nHECnHPCnCMHEC天然大分子材料化學(xué)Cyanoethyl cellulosenCellulose readily reacts with olefins containing polar substituentsnThe reaction proceeds particularly smoothly where R is H and Y, is a strongly electron-withdrawing group shuch as CN, -CONH2 or SO2R天然大分子材料化學(xué)Deoxy cellulosenMost in

10、volve displacement of a good leaving group,e.g., a tosylate（甲苯磺?；?or mesylate（甲磺?；ゞroup by a halide, nitrate or sulfate via an SN2 nucleophilic substitution type reaction nHalodeoxy celluloses are prepared by the nucleophilic displacement of a good leaving group by halides in a variety of solvents

11、X= F, Cl, Br or I天然大分子材料化學(xué)Cellulose carbamatesnThe reaction medium is usually pyridine but homogeneous reactions have been recently descibed. The degree of substituion (D.S.) of 3 is easily obtainablenReaction of cellulose with diisocyanates have been used to crosslink cellulose天然大分子材料化學(xué)Cellulose xa

12、nthatenThe formation of cellulose xanthate is employed in the viscose rayon process. Commerically, a vapor phase process is usednThe D.S. Values are low (ca. 1-1.5) as this is sufficient for solubilization of the xanthate in aqueous NaOH for the wet spinning of viscose rayon fibers天然大分子材料化學(xué)Reduction

13、 of cellulosenThe most convenient method for the reduction of aldehydes and ketones is to use metal hydrides such as lithium aluminum hydride and sodium borohydride. The carbonyl group is reduced to give primary or secondary alcohols nAs a result this procedure can only be applied to cellulose that

14、have been oxidized to give aldehyde or carboxylic groups天然大分子材料化學(xué)Cellulose graft copolymernThe first method involves reacting the cellulose (via its OH groups) with a performed polymer having a reactive end groupnIn the second method, an active species (free radical or ion) is generated on the cellu

15、lose backbone, which initiates the polymerization of monomers天然大分子材料化學(xué)木質(zhì)素（Lignin）n在植物界中是僅次于纖維素的天然有機(jī)高分子n其不溶于水，只能溶于強(qiáng)堿與亞硫酸鹽溶液中n屬芳香族類，其中含有羥基、甲氧基和羰基等天然大分子材料化學(xué)Lignin biopolymernAlkylation and dealkylation（烷化和脫烷）nMethylolation（羥甲基化）nAmination（胺化）nCarboxylation and acylation（羧化和?；﹏Halogenation and nitration（鹵化和硝化）nHydrogenolysis（氫解）nOxidation and Reduction（氧化還原）nSulfomethylation（磺甲基化）nSulfonation（磺化）nNitroxide formation（硝基氧化）nSilylation（硅烷化）nPhosphorylation（磷酸化）nGrafting and Oxyalkylation（接枝和烷氧基化）天然大分子材料化學(xué)AlkylationnReaction with diazoalkanes（重氮烴類）nReaction with alcohols in t