萬(wàn)濤,王博,韓慶,劉奎仁,王玉江,魏世丞,
納米TiO2改性環(huán)氧樹(shù)脂的制備技術(shù)與性能研究進(jìn)展
萬(wàn)濤1,王博2,韓慶1,劉奎仁1,王玉江2,魏世丞1,2
(1.東北大學(xué),沈陽(yáng) 110819;2.陸軍裝甲兵學(xué)院,北京 100072)
環(huán)氧樹(shù)脂是性能優(yōu)異的熱固性材料,因具備良好的耐腐蝕性、熱穩(wěn)定性及力學(xué)性能,被廣泛應(yīng)用于航空航天、石油化工、艦船、海洋等領(lǐng)域。環(huán)氧樹(shù)脂的高交聯(lián)結(jié)構(gòu)使其韌性及脆性較差,應(yīng)用受限,高性能環(huán)氧樹(shù)脂的制備已成為研究熱點(diǎn)。概述了納米TiO2改性環(huán)氧樹(shù)脂制備技術(shù),主要包括機(jī)械攪拌法、超聲法、機(jī)械攪拌和超聲結(jié)合法、珠磨法和化學(xué)物理結(jié)合法等。同時(shí)歸納了各制備技術(shù)的原理及各制備技術(shù)對(duì)納米TiO2在環(huán)氧樹(shù)脂中分散性的影響和存在的不足。重點(diǎn)綜述了納米TiO2改善環(huán)氧樹(shù)脂的相關(guān)性能,主要包括力學(xué)性能、耐腐蝕性能、防污損性能及耐候性能等。TiO2可與環(huán)氧樹(shù)脂發(fā)生接枝反應(yīng),改善環(huán)氧樹(shù)脂的結(jié)構(gòu),提高復(fù)合材料的力學(xué)性能;此外,TiO2的填入可有效提高復(fù)合材料的致密度,減小孔隙率,降低表面能,提高其耐腐蝕性能;TiO2/EP復(fù)合材料利用TiO2的光催化性能及吸收紫外光性能,大大改善了環(huán)氧樹(shù)脂的防污損性能及耐候性能。最后對(duì)TiO2/EP復(fù)合材料的下一步研究進(jìn)行了展望。
環(huán)氧樹(shù)脂;納米TiO2;復(fù)合;制備技術(shù);性能;TiO2/EP
隨著科技的發(fā)展,復(fù)合材料成為未來(lái)極具潛力的材料之一,其中高分子量材料已成為近年來(lái)最熱的材料。環(huán)氧樹(shù)脂(EP)作為一類(lèi)高性能的熱固性聚合物,由于具備質(zhì)量輕、密度高、黏度大、成本低等優(yōu)點(diǎn),被廣泛應(yīng)用于航空航天、石油化工、艦船、海洋等領(lǐng)域。但環(huán)氧樹(shù)脂較高的交聯(lián)結(jié)構(gòu)使其脆性和韌性較差,且固化后環(huán)氧樹(shù)脂中羥基含量較高,限制了其應(yīng)用范圍[1-4]。為進(jìn)一步提高環(huán)氧樹(shù)脂性能、拓展環(huán)氧樹(shù)脂應(yīng)用領(lǐng)域,需將環(huán)氧樹(shù)脂進(jìn)行改性,目前改性環(huán)氧樹(shù)脂的技術(shù)有化學(xué)法和物理法[5]?;瘜W(xué)法[4,6-7]是指通過(guò)化學(xué)的方法在環(huán)氧基團(tuán)或羥基上引入軟鏈或硬鏈,從而改善環(huán)氧樹(shù)脂的韌性和硬度的方法。物理法[8-10]是通過(guò)引入無(wú)機(jī)填料,使環(huán)氧樹(shù)脂形成有機(jī)–無(wú)機(jī)復(fù)合材料的方法。物理填料法是一類(lèi)用于處理復(fù)合材料表面缺陷的方法,該方法能達(dá)到填充、流平、保護(hù)和絕緣基板等目的,已成為改善環(huán)氧樹(shù)脂性能的有效技術(shù)[11]。與微米級(jí)等粒徑較大粒子作為填料形成的傳統(tǒng)復(fù)合材料相比,將納米粒子摻入聚合物基質(zhì)中可以更好地改善材料的特性,特別是材料的韌性和剛度[12-13],納米粒子作為填料組成的復(fù)合材料已成為研究熱點(diǎn)[14]。
目前,納米填料多種多樣,如SiO2[15]、TiO2[16-17]、ZnO[18-20]、CaCO3[21-22]、SnO2[23]、Fe3O4[24-25]、石墨烯[26]、氧化石墨烯(GO)[27]、碳納米管[28]、BN[29]等,將這些納米填料加入環(huán)氧樹(shù)脂中可顯著提高環(huán)氧樹(shù)脂的力學(xué)性能、防腐性能、耐候性能及其他特殊性能。其中納米TiO2因具有無(wú)毒、較好的化學(xué)穩(wěn)定性、較好的光穩(wěn)定性、較好的防腐性、較好的電性能、較好的相容性、高光催化活性、高折射率和可吸收紫外光等優(yōu)異性能[30-31],而成為改善環(huán)氧樹(shù)脂的主要填料。目前常見(jiàn)的TiO2晶體結(jié)構(gòu)主要有3種:金紅石相、銳鈦礦相和板鈦礦相,如圖1a和b所示,3種不同晶體結(jié)構(gòu)TiO2的共同點(diǎn)是基本單元都是TiO6八面體。金紅石型和板鈦礦型結(jié)構(gòu)都是由TiO6八面體共點(diǎn)且共邊組成,而銳鈦礦型是由TiO6八面體共邊組成,板鈦礦型TiO2幾乎不具備光催化活性,且熱穩(wěn)定性差,研究?jī)r(jià)值低。銳鈦礦型實(shí)際上是一種四面體結(jié)構(gòu),金紅石型是晶格稍有畸變的八面體結(jié)構(gòu)。如圖1c—e所示,組成金紅石型的TiO6八面體是沿對(duì)角線方向拉長(zhǎng)的八面體,銳鈦礦型八面體是由金紅石型八面體中的2個(gè)沿著四重軸方向的Ti—O鍵進(jìn)一步畸變而成的,金紅石型相為微成斜方晶,銳鈦礦型八面體呈明顯斜方晶型畸變。
文中重點(diǎn)歸納了納米TiO2改性環(huán)氧樹(shù)脂的制備技術(shù)及綜述了TiO2改性環(huán)氧樹(shù)脂的性能,以期為拓寬環(huán)氧樹(shù)脂的應(yīng)用及其相關(guān)研究提供一定的參考價(jià)值。
目前制備TiO2/EP復(fù)合材料的方法主要有2種:將TiO2直接作為填料加入環(huán)氧樹(shù)脂中;將TiO2改性為T(mén)iO2漿料,以漿料形式與環(huán)氧樹(shù)脂混合制備TiO2/EP復(fù)合材料?,F(xiàn)有的制備技術(shù)有機(jī)械攪拌法、超聲法、機(jī)械攪拌和超聲結(jié)合法、珠磨法和化學(xué)物理結(jié)合法,下面將進(jìn)行一一敘述。
圖1 TiO2結(jié)構(gòu)單元連接方式與結(jié)構(gòu)示意圖
機(jī)械攪拌法是利用攪拌產(chǎn)生的剪切力將TiO2分散到環(huán)氧樹(shù)脂中的技術(shù)。Singh等[32]采用機(jī)械攪拌技術(shù),將TiO2分散至環(huán)氧樹(shù)脂中,制備了TiO2/EP復(fù)合材料。Carballeira等[33]通過(guò)環(huán)磨攪拌裝置混合TiO2和環(huán)氧樹(shù)脂,制備了TiO2/EP復(fù)合材料,攪拌裝置如圖2a所示。圖2b—d為納米TiO2原料的SEM圖及復(fù)合材料的TEM圖,據(jù)圖2b—d可知,該技術(shù)可明顯改善TiO2在環(huán)氧樹(shù)脂中的分散性,且團(tuán)聚顆粒直徑在100~250 nm左右,已達(dá)到較好的分散效果。Huo等[34]將TiO2制備成漿料,通過(guò)電動(dòng)攪拌機(jī)攪拌技術(shù)將它均勻分散在水性環(huán)氧樹(shù)脂中,制備出具有良好光催化性能的TiO2/EP復(fù)合材料。上述研究表明,通過(guò)攪拌技術(shù)制備TiO2/EP具備可行性,TiO2可均勻地分散在環(huán)氧樹(shù)脂中。
圖2 環(huán)磨攪拌裝置示意圖與TiO2原料及其分散圖[33]
超聲法的原理是將超聲波發(fā)射到TiO2/EP的混合物中,產(chǎn)生大量空化泡,空化泡達(dá)到臨界直徑發(fā)生內(nèi)爆,內(nèi)爆產(chǎn)生的激波和空化振蕩產(chǎn)生的微交叉流相結(jié)合,將TiO2/EP中大直徑TiO2顆粒擊碎,從而使固液充分混合達(dá)到分散效果[35]。
Ng等[36]制備了TiO2/EP復(fù)合材料,在該復(fù)合材料中,TiO2可均勻分散在環(huán)氧樹(shù)脂中,但仍存在少量團(tuán)簇現(xiàn)象。Bittmann等[35]通過(guò)超聲法制備出了具有良好分散穩(wěn)定性的TiO2/EP復(fù)合材料,研究表明,超聲時(shí)間的延長(zhǎng)、振幅的升高、體積的增大均有利于制備出具有良好分散穩(wěn)定性的TiO2/EP復(fù)合材料,且球磨顆粒分散模型中的Winkler模型與該超聲分散過(guò)程吻合,該模型擬合公式為:
式中:D為時(shí)刻的顆粒直徑;為時(shí)間;A為初始顆粒直徑;E為最終顆粒直徑;eff為有效分散體積;T為總超聲體積;為時(shí)間常數(shù)。
Guo等[37]將稀釋劑和TiO2混合,以一定比例添加至環(huán)氧樹(shù)脂中,通過(guò)超聲法制備出了TiO2/EP復(fù)合材料,該材料有利于提高OPC(普通水泥)漿料的力學(xué)性能和聯(lián)接性。
以上研究表明,機(jī)械攪拌法和超聲法均可制備出TiO2/EP復(fù)合材料,但復(fù)合材料的分散穩(wěn)定性有限,故大量學(xué)者將2種技術(shù)結(jié)合,制備出了具有良好分散穩(wěn)定性的復(fù)合材料。
機(jī)械攪拌和超聲結(jié)合法制備TiO2/EP復(fù)合材料有3種方式,分別為超聲和機(jī)械攪拌同時(shí)進(jìn)行(超聲雙混合法,UDM)、先機(jī)械攪拌后超聲混合及先超聲后機(jī)械攪拌。
圖3a為UDM裝置示意圖,Kumar等[38]添加丁酮(MEK)對(duì)納米TiO2與環(huán)氧樹(shù)脂的混合液進(jìn)行稀釋后,通過(guò)UDM法制備了TiO2/EP復(fù)合材料,復(fù)合材料的場(chǎng)發(fā)射掃描電鏡(FESEM)圖如圖3c—e所示,相較于圖3b可知,UDM法能提高TiO2在環(huán)氧樹(shù)脂中的分散性,且當(dāng)TiO2的質(zhì)量分?jǐn)?shù)高達(dá)15%時(shí),納米TiO2粒徑為65~130 nm,故該技術(shù)制備的復(fù)合材料分散穩(wěn)定性較好。
圖3 UDM裝置示意圖及不同質(zhì)量分?jǐn)?shù)的TiO2/EP超聲或UDM處理后FESEM圖[38]
Srivastava等[39]將TiO2進(jìn)行硅烷改性,通過(guò)先機(jī)械攪拌后超聲的方法制備了TiO2/EP復(fù)合材料,結(jié)果表明,當(dāng)TiO2的質(zhì)量分?jǐn)?shù)高于5%時(shí),復(fù)合材料會(huì)存在團(tuán)簇現(xiàn)象。圖4a為T(mén)iO2/EP納米復(fù)合材料制備工藝示意圖,Goyat等[40]采用如圖4a所示的先機(jī)械攪拌后超聲的方法制備了TiO2/EP復(fù)合材料。圖4b為T(mén)iO2原料的TEM圖及其選區(qū)電子衍射(SAED)圖,圖4c—e為不同TiO2含量TiO2/EP在低倍和高倍下的AFM圖,從圖4b—e可知,納米TiO2在環(huán)氧樹(shù)脂中仍保持較好的分散性,納米TiO2團(tuán)簇尺寸隨著TiO2含量的增加而變大,而在高倍率的原子力顯微鏡(AFM)圖(見(jiàn)圖4c2—e2)中可以發(fā)現(xiàn),當(dāng)TiO2的質(zhì)量分?jǐn)?shù)為5%時(shí),復(fù)合材料的分散穩(wěn)定性較好,而TiO2的質(zhì)量分?jǐn)?shù)為10%和20%時(shí),團(tuán)簇現(xiàn)象較為明顯。他們對(duì)分散性進(jìn)行了定量分析,發(fā)現(xiàn)當(dāng)納米TiO2的質(zhì)量分?jǐn)?shù)為0.5%~10%時(shí),納米顆粒平均團(tuán)簇尺寸為50~257 nm,顆粒均勻長(zhǎng)大,而當(dāng)TiO2的質(zhì)量分?jǐn)?shù)為10%~20%時(shí),納米粒子團(tuán)簇尺寸顯著增大至547~ 1 124 nm。采用式(2)表示粒子間距離()和填料含量()的關(guān)系。
圖4 TiO2/EP納米復(fù)合材料制備工藝示意圖、TiO2原料TEM圖及TiO2/EP質(zhì)量分?jǐn)?shù)不同時(shí)的AFM圖[40]
式中:表示顆粒直徑。納米粒子之間的團(tuán)簇使TiO2顆粒間距的理論值和實(shí)驗(yàn)值之間的偏差隨著TiO2含量的增加而增大,且實(shí)驗(yàn)值總是大于理論值。
Bittmann等[41]通過(guò)先機(jī)械攪拌后超聲的方法制備了TiO2/EP復(fù)合材料,研究表明,在超聲作用下,混合物會(huì)形成一種流動(dòng)現(xiàn)象,達(dá)到攪拌效果,這表明機(jī)械攪拌不會(huì)影響超聲處理后復(fù)合材料的分散穩(wěn)定性。Huang等[42]通過(guò)先超聲后機(jī)械攪拌的方法制備了TiO2/EP納米復(fù)合涂層,研究表明,當(dāng)TiO2的質(zhì)量分?jǐn)?shù)在3%以?xún)?nèi)時(shí),復(fù)合材料的分散穩(wěn)定性較好,但TiO2含量繼續(xù)增加,TiO2團(tuán)簇現(xiàn)象更為明顯。
攪拌和超聲結(jié)合法制備TiO2/EP復(fù)合材料的研究表明,UDM法大大提高了TiO2/EP復(fù)合材料的分散穩(wěn)定性,而另外2種技術(shù)制備的復(fù)合材料會(huì)存在團(tuán)簇現(xiàn)象。
珠磨離心法是一種有效分散液體中顆粒的機(jī)械加工法,其工作示意圖如圖5所示。將含有團(tuán)簇TiO2的環(huán)氧樹(shù)脂漿液流入容器的分散部位,使?jié){液與劇烈攪拌的磨珠相互作用,隨后漿液達(dá)到分散區(qū)上部,在離心力作用下與磨珠分離,磨珠繼續(xù)留在珠磨機(jī)內(nèi),漿液則被泵出容器,團(tuán)簇顆粒收集到攪拌槽中,循環(huán)往復(fù)[43]。
圖5 單軸珠磨示意圖[44]
Ogi等[44]利用珠磨法研究了針型和球型納米TiO2在水中的分散情況,結(jié)果表明,珠磨離心法可改善納米TiO2在水中的分散穩(wěn)定性。Wang等[45]先通過(guò)簡(jiǎn)單化學(xué)合成法得到DA/meso–TiO2復(fù)合材料,再通過(guò)珠磨離心法制備了DA/meso–TiO2/EP復(fù)合材料,但未具體討論珠磨法對(duì)納米TiO2在環(huán)氧樹(shù)脂中的分散作用。Inkyo等[43]通過(guò)珠磨離心法制備了TiO2/EP復(fù)合材料,研究表明,在該方法下,未經(jīng)化學(xué)處理的納米TiO2也能有效地將納米顆粒分散,小粒徑的珠粒更有利于提高復(fù)合材料的分散穩(wěn)定性,當(dāng)磨珠粒徑為8 μm時(shí),珠磨后的納米TiO2粒徑可分散至15 nm左右,該方法具有廣泛的應(yīng)用前景和價(jià)值。
上述制備技術(shù)表明,不同物理制備技術(shù)均能提高TiO2/EP復(fù)合材料的分散穩(wěn)定性,但TiO2與環(huán)氧樹(shù)脂仍存在相容性問(wèn)題,有學(xué)者嘗試通過(guò)化學(xué)物理結(jié)合法提高TiO2/EP復(fù)合材料的相容性,從而提高復(fù)合材料的分散穩(wěn)定性。
化學(xué)物理結(jié)合法一般是利用有機(jī)物改性TiO2或環(huán)氧樹(shù)脂,使其表面被修飾成特定的官能團(tuán)[46-48],從而提高TiO2與環(huán)氧樹(shù)脂的相容性,后通過(guò)物理共混法將TiO2分散在環(huán)氧樹(shù)脂中,從而改善TiO2/EP復(fù)合材料的分散穩(wěn)定性的方法。
化學(xué)物理結(jié)合法改性主要是分為3種:用硅烷偶聯(lián)劑或酸酯類(lèi)物質(zhì)對(duì)TiO2進(jìn)行改性;利用硅氧烷或樹(shù)脂類(lèi)物質(zhì)對(duì)環(huán)氧樹(shù)脂進(jìn)行改性;分別對(duì)TiO2和環(huán)氧樹(shù)脂進(jìn)行改性。Guan等[16]利用溶膠凝膠法以三乙氧基硅烷封端的三疏基硫乙胺(TCTMTEA)為偶聯(lián)劑制備了TiO2/EP復(fù)合材料。Radoman等[49]用丙基沒(méi)食子酸酯(PG)、已基沒(méi)食子酸酯(HG)及十二烷基沒(méi)食子酸酯(LG)3種沒(méi)食子酸酯對(duì)TiO2進(jìn)行改性,分別合成了PG–TiO2/EP、HG–TiO2/EP和LG– TiO2/EP等3種復(fù)合材料。Srivastava等[39]通過(guò)超聲法用γ–縮水甘油醚氧丙基三甲氧基硅烷(GPTMS)對(duì)TiO2進(jìn)行硅烷改性,制備了TiO2/EP復(fù)合材料,該復(fù)合材料在TiO2含量較低時(shí)分散穩(wěn)定性良好,但在TiO2含量較高時(shí)存在團(tuán)簇現(xiàn)象。Ahmad等[50]用端羥基聚二甲基硅氧烷(HPDMS)改性環(huán)氧樹(shù)脂,制備了TiO2/ HPDMS–EP復(fù)合材料。Chen等[17]將用鈦酸酯偶聯(lián)劑(TCA201)改性得到的納米TiO2和用聚氨酯(PU)改性得到的環(huán)氧樹(shù)脂混合,后經(jīng)超聲法處理,制備得到了TiO2/EP–PU復(fù)合材料。圖6a和b分別為納米TiO2改性前后的SEM圖,比較圖6a和b可知,改性后的TiO2顆粒粒徑更小,表明聚氨酯可改善TiO2顆粒分散性。復(fù)合材料的形貌如圖6c和d所示,納米TiO2均勻分布在EP–PU基體中,具有良好的分散穩(wěn)定性。圖6e和f表明,修飾后的TiO2納米顆粒表面接枝了—CH(CH3)2基團(tuán),TiO2納米顆粒通過(guò)末端偶聯(lián)劑與之相連,活性基團(tuán)能與有機(jī)相相容,從而促進(jìn)了兩相界面的相互滲透,改善了TiO2整體的分散性,提高了環(huán)氧樹(shù)脂的整體性能。
但上述研究都沒(méi)有具體研究偶聯(lián)劑是否能改善TiO2在環(huán)氧樹(shù)脂中的分散性,而是通過(guò)物理制備技術(shù)使TiO2在環(huán)氧樹(shù)脂中達(dá)到良好分散性的要求。Liu等[51]指出,采用硅烷偶聯(lián)劑可以提高TiO2–GO/EP復(fù)合材料的分散穩(wěn)定性,他們分別合成了TiO2– GO/EP復(fù)合材料和f–TiO2–GO/EP,研究表明,經(jīng)硅烷偶聯(lián)劑修飾后的材料的分散性更好,而未改性的復(fù)合材料中存在明顯的團(tuán)簇現(xiàn)象。Xiong等[52]采用超支化聚丙酸乙酯(HPBPEA)對(duì)TiO2進(jìn)行改性,TiO2– HPBPEA在環(huán)氧樹(shù)脂中的分散性明顯優(yōu)于TiO2在環(huán)氧樹(shù)脂中的分散性,TiO2–HPBPEA分散粒徑達(dá)200 nm左右,無(wú)團(tuán)聚現(xiàn)象。以上研究表明,將TiO2改性可以改善它在環(huán)氧樹(shù)脂中的分散性。
復(fù)合材料良好的分散穩(wěn)定性是改善環(huán)氧樹(shù)脂性能的重要前提,5種制備技術(shù)的優(yōu)缺點(diǎn)見(jiàn)表1,上述5種制備技術(shù)均能改善復(fù)合材料的分散穩(wěn)定性,但仍存在少量團(tuán)簇現(xiàn)象,這將對(duì)提高環(huán)氧樹(shù)脂性能造成不利影響,故進(jìn)一步改善復(fù)合材料的分散穩(wěn)定性仍值得研究。
圖6 不同納米復(fù)合物SEM圖、TCA201–TiO2的FT–TR圖及TEM圖[17]
表1 不同制備技術(shù)優(yōu)缺點(diǎn)
Tab.1 Advantages and disadvantages of different preparation techniques
將TiO2填入EP中制備TiO2/EP復(fù)合材料,旨在利用TiO2優(yōu)異的物理化學(xué)等性能,提高環(huán)氧樹(shù)脂的力學(xué)性能、耐腐蝕性能、防污損性能及耐候性能等,拓寬環(huán)氧樹(shù)脂的應(yīng)用領(lǐng)域。
環(huán)氧樹(shù)脂高度的交聯(lián)結(jié)構(gòu)使其韌性和抗沖擊性較差,且抗沖擊性較差的地方易產(chǎn)生裂紋,因此在不犧牲環(huán)氧樹(shù)脂其他重要特性的前提下,如何提高環(huán)氧樹(shù)脂的韌性成為了主要研究方向。
將TiO2和環(huán)氧樹(shù)脂復(fù)合后,諸多研究表明復(fù)合材料的韌性、耐劃傷性、模量等力學(xué)性能均得到明顯的改善[17,36,38-39,41],特別是Carballeira等[33]制備的TiO2/EP復(fù)合材料,相比于純環(huán)氧樹(shù)脂,模量、強(qiáng)度和韌性分別提高了48%、10%和102%。還有研究表明,雖然TiO2/EP復(fù)合材料大部分力學(xué)性能均得到了一定提高,但復(fù)合材料韌性卻有所下降[40,53]。Huang等[42]制備TiO2/EP復(fù)合材料的FTIR光譜表明,納米TiO2和環(huán)氧樹(shù)脂之間會(huì)產(chǎn)生氫鍵。Ai等[54]合成了TiO2–雙丁二醇酯(BDPET)–EP復(fù)合材料,如圖7a和b所示,TiO2在BDPET–EP中作為成核劑和物理結(jié)點(diǎn),提高了分子鏈的纏結(jié),使復(fù)合物分子鏈連接更為緊密,從而提高了復(fù)合材料的抗拉強(qiáng)度、沖擊強(qiáng)度和剪切強(qiáng)度。當(dāng)TiO2添加量過(guò)高時(shí),TiO2納米顆粒會(huì)發(fā)生團(tuán)聚,使物質(zhì)內(nèi)部結(jié)構(gòu)不均,從而大大降低了復(fù)合材料的力學(xué)性能。圖7d—f為沖擊試樣的SEM圖,從圖7d可知,純環(huán)氧樹(shù)脂的斷裂表面較光滑,斷裂部位呈脆性斷裂,由圖7e可知,兩相混合物的結(jié)構(gòu)可以提高環(huán)氧樹(shù)脂的韌性,圖7f可說(shuō)明納米TiO2的引入可以提高涂層韌性、有效防止裂紋擴(kuò)展;Ai又指出TiO2與環(huán)氧樹(shù)脂中存在氫鍵,氫鍵可進(jìn)一步提高環(huán)氧樹(shù)脂的韌性。如圖7c所示,Goyat等[40]研究也表明,當(dāng)環(huán)氧樹(shù)脂中添加TiO2納米粒子后,拉伸導(dǎo)致O—H向低波長(zhǎng)方向移動(dòng),且最大可移動(dòng)到3 434 cm?1處,這也表明TiO2與環(huán)氧樹(shù)脂中可能存在氫鍵。
“從直升機(jī)上俯瞰,金沙江下游的羊拉、奔子欄、拖頂、塔城、巨甸、上江、石鼓、虎跳峽經(jīng)濟(jì)開(kāi)發(fā)區(qū)等地的大部分地區(qū)一片汪洋。”云南電網(wǎng)帶電作業(yè)分公司機(jī)巡中心機(jī)長(zhǎng)史星波11月14日接到任務(wù)從香格里拉縣上江鄉(xiāng)沿金沙江逆流而上開(kāi)展直升機(jī)巡視,進(jìn)行水情監(jiān)測(cè)、災(zāi)情勘察和變電設(shè)備線路巡查工作。這是云南電網(wǎng)首次將直升機(jī)應(yīng)用于應(yīng)急處置,兩天時(shí)間累計(jì)飛行了10小時(shí)25分鐘?!爸鄙龣C(jī)在特殊應(yīng)急工作中具有響應(yīng)迅速、排查范圍廣、受沿線交通情況限制少等優(yōu)勢(shì)?!笔沸遣ㄕf(shuō),通過(guò)直升機(jī)巡視能第一時(shí)間掌握災(zāi)情資料,方便后續(xù)開(kāi)展應(yīng)急指揮。
上述研究表明,TiO2與環(huán)氧樹(shù)脂的復(fù)合可有效提高環(huán)氧樹(shù)脂的力學(xué)性能,且環(huán)氧樹(shù)脂與TiO2之間的交聯(lián)結(jié)構(gòu)和氫鍵可增強(qiáng)環(huán)氧樹(shù)脂的韌性。
環(huán)氧樹(shù)脂在作為涂層服役時(shí)會(huì)產(chǎn)生局部缺陷,這些缺陷會(huì)作為水、氧及腐蝕性物質(zhì)進(jìn)入金屬基體的通道,導(dǎo)致產(chǎn)生局部腐蝕;且環(huán)氧樹(shù)脂為親水性材料,固化后體積收縮較大,能吸收周?chē)h(huán)境中的水分。固化后環(huán)氧樹(shù)脂涂層中的孔隙會(huì)吸收水分及其他物質(zhì),這些物質(zhì)遷移到環(huán)氧–金屬界面處,會(huì)產(chǎn)生金屬基體的腐蝕和金屬基體與涂層的分層[55-56]。含有納米粒子的環(huán)氧涂層具有顯著的防腐蝕屏障性能[57-58],在環(huán)氧樹(shù)脂中填入納米TiO2,可以填充涂層中的孔隙、減小孔隙率和涂層中的缺陷,使腐蝕物質(zhì)難以與基體接觸,提高環(huán)氧涂層的阻隔性能[59-61]。
圖7 不同納米TiO2含量時(shí)BDPET–EP(質(zhì)量分?jǐn)?shù)為4%)的抗拉強(qiáng)度、沖擊強(qiáng)度、剪切強(qiáng)度圖、TiO2–EP的FT–IR圖[36]及沖擊不同試樣的SEM圖[54]
Liu等[51]分別合成了4種不同的復(fù)合材料,與純環(huán)氧樹(shù)脂涂層相比,TiO2–GO–f–EP涂層的腐蝕電流密度降低了2個(gè)數(shù)量級(jí)。張山等[62]合成的聚苯胺– TiO2/EP復(fù)合材料具有良好的耐Cl?和S2?腐蝕能力。Wang等[45]以多巴胺(DA)改性多孔TiO2,分別制備了DA–TiO2/EP和TiO2/EP復(fù)合材料,研究結(jié)果如圖8—10所示,圖8為含4種不同填料的EP在不同浸泡時(shí)間下的奈奎斯特圖,比較圖8a和8b可知,當(dāng)環(huán)氧樹(shù)脂與TiO2復(fù)合后,電容弧的直徑均明顯變大,表明當(dāng)環(huán)氧樹(shù)脂中填入TiO2后,環(huán)氧樹(shù)脂的防腐性能顯著提高;又根據(jù)圖8c和d可知,改性后的TiO2能進(jìn)一步提高環(huán)氧樹(shù)脂的防腐性能。圖9為試樣在質(zhì)量分?jǐn)?shù)為3.5%的NaCl溶液中浸泡不同時(shí)間時(shí)的伯德圖,由圖9可知,在浸泡不同時(shí)間后,無(wú)論是在高頻還是低頻情況下,當(dāng)相同頻率時(shí),阻抗大小均是DA–TiO2/EP>TiO2/EP>EP,證明了上述結(jié)論。圖10為鹽霧實(shí)驗(yàn)結(jié)果圖,據(jù)圖10可知,純環(huán)氧樹(shù)脂涂層腐蝕速率最快,而TiO2/EP銹量明顯減少,而DA– TiO2/EP涂層的銹蝕更少,該結(jié)果和EIS實(shí)驗(yàn)結(jié)果一致,表明改性后的TiO2更能改善環(huán)氧樹(shù)脂的防腐性能。
Al-maadeed等[63]制備了二氧化鈦納米管(TNT)–EP復(fù)合材料,與純環(huán)氧樹(shù)脂涂層相比,TNT–EP復(fù)合材料的防腐性能得到了顯著改善。圖11a和b為不同涂層的接觸角示意圖,如圖11a和b所示,純環(huán)氧樹(shù)脂涂層的接觸角為32.74°,而TNT–EP涂層的接觸角為64.3°,涂層接觸角的變大提高了TNT–EP涂層的疏水性,從而提高了涂層的防腐性能。觀察不同時(shí)間下劃傷涂層的形貌,結(jié)果如圖11c和d所示,從圖11c可以明顯看出,涂層劃傷后有較長(zhǎng)且深的劃痕,經(jīng)過(guò)5 d后,劃痕明顯消失(見(jiàn)圖11d)。環(huán)氧樹(shù)脂從TNT中釋放到劃痕中,隨后與介孔SiO2中的固定化胺接觸后繼續(xù)交聯(lián),使涂層損傷部位幾乎完全自愈,TNT–EP涂層的特殊結(jié)構(gòu)使該涂層具有自修復(fù)功能,達(dá)到了改善環(huán)氧樹(shù)脂防腐性能的目的。
防腐測(cè)試表明,TiO2/EP復(fù)合材料的防腐性能遠(yuǎn)遠(yuǎn)優(yōu)于純EP材料的防腐性能,且TiO2和EP經(jīng)修飾后再?gòu)?fù)合能進(jìn)一步提高復(fù)合材料的防腐性能;復(fù)合材料的特殊結(jié)構(gòu)使它具有自修復(fù)功能,可增強(qiáng)復(fù)合材料的防腐性能,為防腐技術(shù)的發(fā)展提供了新的研究方向。
圖8 含4種不同填料的EP在不同時(shí)間浸泡下的奈奎斯特圖[45]
圖9 試樣在3.5% NaCl溶液中浸泡不同時(shí)間的伯德圖[45]
圖10 鹽霧試驗(yàn)600 h后填料質(zhì)量分?jǐn)?shù)不同時(shí)EP涂層的表面形貌[45]
圖11 接觸角圖和涂層劃傷后不同時(shí)間下的SEM圖[63]
生物污染對(duì)公共設(shè)施、醫(yī)療設(shè)備和軍工裝備等設(shè)施設(shè)備來(lái)說(shuō)是不可避免的問(wèn)題[64-65]。生物污損主要經(jīng)歷4個(gè)過(guò)程[66]:條件膜、初級(jí)定殖、二級(jí)定殖和三級(jí)定殖,可針對(duì)污染階段采用脫污、阻污和抗菌等方法來(lái)進(jìn)行防污[67-68],以制備出優(yōu)良防污涂料對(duì)基體進(jìn)行保護(hù)。環(huán)氧樹(shù)脂具有強(qiáng)度高、附著力好、抗彎性好等優(yōu)點(diǎn),被廣泛用于表面防護(hù);二氧化鈦具有優(yōu)異的光催化性能。當(dāng)輻射光能量≥3.2 eV時(shí),TiO2價(jià)帶上電子吸收光能后,被激發(fā)至導(dǎo)帶上,生成激發(fā)態(tài)電子(e?),而在價(jià)帶上生成空穴(h+),e?與吸附在TiO2表面的氧分子(O2)發(fā)生還原反應(yīng),產(chǎn)生氧分子自由基(O2?),氧分子自由基(O2?)與H+進(jìn)一步反應(yīng)生成H2O2,同時(shí),h+與H2O、OH?發(fā)生氧化反應(yīng)生成活性很強(qiáng)的羥基自由基(OH),羥基自由基(OH)和H2O2將吸附于TiO2表面的有機(jī)物上,進(jìn)而分解成CO2和H2O等,TiO2將吸附于表面的無(wú)機(jī)物上進(jìn)而還原或氧化成礦化物,從而可將二氧化鈦和環(huán)氧樹(shù)脂復(fù)合達(dá)到防污效果。
Huo等[34]制備了TiO2/EP復(fù)合材料,結(jié)果表明,相比于純水性環(huán)氧樹(shù)脂,復(fù)合材料降解羅明丹B的效率提高了2倍。Syed等[69]通過(guò)共混法制備了TiO2/EP復(fù)合材料,該復(fù)合材料對(duì)采油污水中的有機(jī)物有降解作用。Nardi等[70]制備了濃度可控的Fe3O4@TiO2核殼/環(huán)氧樹(shù)脂復(fù)合材料,該復(fù)合材料具有較好的抗菌性能。以上結(jié)果均表明,TiO2的填入可提高環(huán)氧樹(shù)脂的防污損能力。Santhosh等[71]制備了Ag–TiO2/EP復(fù)合材料,其抗菌性能如圖12所示,圖12a和b表明,在紫外光照下,相比于純環(huán)氧樹(shù)脂表面,大腸桿菌和金黃色葡萄球菌生物膜在TiO2/EP復(fù)合材料表面均不易形成,且Ag的填入進(jìn)一步使復(fù)合材料生物膜難以形成。圖12c表明,納米TiO2與環(huán)氧樹(shù)脂復(fù)合后,有利于抑制細(xì)菌生長(zhǎng),且Ag的填入能進(jìn)一步提高環(huán)氧樹(shù)脂的抑菌性能。為了探究復(fù)合涂層的抑菌活性,比較了黑暗和光照條件下的抑菌率,如圖12d和e所示,結(jié)果表明,在黑暗條件下,TiO2/EP復(fù)合材料對(duì)大腸桿菌和金黃色葡萄球菌的抑制率分別為13%和6%,而在紫外光照下,該復(fù)合材料對(duì)大腸桿菌和金黃色葡萄球菌的抑制率分別提高至56%和45%,而EP/Ag–TiO2無(wú)論是在黑暗還是在紫外光照射下,抑菌率均高于EP/TiO2,表明在紫外光照下,TiO2的光催化活性被激發(fā),能有效發(fā)揮其抑菌性能,達(dá)到防污效果,而Ag的填入會(huì)促進(jìn)光催化性能,進(jìn)一步提高復(fù)合材料的抑菌性能。
無(wú)論是降解性能還是抗菌性能,TiO2/EP復(fù)合材料的均比純EP的更好,表明復(fù)合后環(huán)氧樹(shù)脂的抗污損性顯著提高,且在紫外光激發(fā)下,TiO2光催化性能較好,能有效發(fā)揮復(fù)合材料的抑菌性能和降解性能,復(fù)合材料的防污損性能得到進(jìn)一步提高,TiO2吸收紫外光也表明復(fù)合材料具有較好的耐候性。
圖12 TiO2、Ag對(duì)大腸桿菌和金黃色葡萄球菌在EP上生存的影響[71]
Li等[73]研究了TiO2/EP復(fù)合材料的耐UV輻射性能,結(jié)果如圖13所示,圖13a表明,TiO2/EP復(fù)合材料對(duì)UV具有良好的吸收性,但TiO2含量過(guò)高會(huì)導(dǎo)致復(fù)合材料對(duì)UV的吸收性降低,這種吸收性可有效防止涂層被紫外線破壞。由圖13b—e可知,純環(huán)氧樹(shù)脂紫外輻射后比輻射前的彎曲截面更加光滑,而TiO2/EP復(fù)合材料在紫外輻射后的彎曲損壞截面圖與輻射前彎曲損壞截面圖類(lèi)似,均表現(xiàn)出較強(qiáng)韌性,表明相比于純環(huán)氧樹(shù)脂,TiO2/EP復(fù)合材料的耐候性大大增強(qiáng)。由圖13d可知,TiO2/EP復(fù)合材料的熱穩(wěn)定性幾乎與純環(huán)氧樹(shù)脂在UV輻射前的熱穩(wěn)定性相當(dāng)。Liu等[51]在UV照射后對(duì)不同涂層進(jìn)行了黏附測(cè)試,其結(jié)果如圖13f所示,結(jié)果表明,當(dāng)紫外照射240 h后,相比于純環(huán)氧樹(shù)脂,當(dāng)環(huán)氧樹(shù)脂改性或在環(huán)氧樹(shù)脂中加入不同填料后,其黏附力損失均減少,而TiO2–GO–EP和TiO2–GO–f–EP涂層相比于其他涂層黏附力損失最小,這可能是TiO2對(duì)紫外光有屏蔽作用,表明TiO2的填入可增強(qiáng)環(huán)氧樹(shù)脂的耐候性。而相比TiO2–GO– EPT涂層,TiO2–GO–f–EP涂層的黏附力損失小,表明GPTMS將環(huán)氧樹(shù)脂改性后提高了涂層的交聯(lián)密度以及TiO2/EP復(fù)合材料的耐候性。上述結(jié)果均表明,TiO2/EP復(fù)合材料對(duì)紫外光具有一定的吸收性,同時(shí)改性環(huán)氧樹(shù)脂會(huì)大大提高TiO2/EP復(fù)合材料的耐候性,但TiO2的光催化性能會(huì)促進(jìn)環(huán)氧樹(shù)脂的老化與降解,目前TiO2/EP不是較好的耐紫外老化涂層,為提高TiO2/EP復(fù)合材料的耐候性,還需對(duì)環(huán)氧樹(shù)脂進(jìn)行改性。
當(dāng)納米材料與環(huán)氧樹(shù)脂復(fù)合后,環(huán)氧樹(shù)脂的某些特定性能也會(huì)發(fā)生變化[74],這些變化將影響環(huán)氧樹(shù)脂的應(yīng)用,當(dāng)納米TiO2復(fù)合環(huán)氧樹(shù)脂后,也有類(lèi)似的現(xiàn)象產(chǎn)生。Guan等[16]制備了TiO2/EP復(fù)合材料,該復(fù)合材料的折射率比純環(huán)氧樹(shù)脂的折射率高,且其折射率與TiO2含量呈線性關(guān)系。Chen等[17]合成了TiO2/ EP–PU復(fù)合材料,該復(fù)合材料的熱分解溫度提高了17.48 ℃。Morselli等[75]研究表明,TiO2的填入將提高環(huán)氧樹(shù)脂的玻璃轉(zhuǎn)變溫度,該復(fù)合材料的玻璃轉(zhuǎn)變溫度在TiO2的質(zhì)量分?jǐn)?shù)為3%時(shí)可達(dá)397.82 ℃,復(fù)合材料的介電常數(shù)也有所升高。Chatterjee等[76]合成了TiO2/EP復(fù)合涂層,納米TiO2的復(fù)合提高了EP的分解溫度,表明納米TiO2的填入可提高EP的熱穩(wěn)定性。根據(jù)Coats–Redfern公式可知,納米TiO2的復(fù)合也提高了環(huán)氧樹(shù)脂的活化能。
圖13 不同含量TiO2改性后的EP的紫外可-可見(jiàn)光吸收光譜圖、疲勞斷裂SEM圖、附著力圖
當(dāng)環(huán)氧樹(shù)脂和TiO2復(fù)合后,復(fù)合材料的力學(xué)性能、防腐性能、防污損性能和耐候性能均顯著優(yōu)于環(huán)氧樹(shù)脂,其他一些性能也有一定提高,大大改善了環(huán)氧樹(shù)脂的綜合性能,拓寬了環(huán)氧樹(shù)脂的應(yīng)用領(lǐng)域。
主要闡述了TiO2/EP制備技術(shù),綜述了TiO2與環(huán)氧樹(shù)脂復(fù)合后,大幅度提高了環(huán)氧樹(shù)脂的力學(xué)性能,特別是增強(qiáng)了環(huán)氧樹(shù)脂的韌性,有助于解決環(huán)氧樹(shù)脂的脆性問(wèn)題,還能利用納米TiO2光催化和納米效應(yīng)大幅度提高環(huán)氧樹(shù)脂的防腐防污及耐候性能等。但是目前仍存在一系列問(wèn)題,主要體現(xiàn)在以下幾個(gè)方面。
1)TiO2在環(huán)氧樹(shù)脂中雖能達(dá)到納米級(jí)的分散,但TiO2在環(huán)氧樹(shù)脂中仍少量存在團(tuán)簇現(xiàn)象,不能更好地改善環(huán)氧樹(shù)脂基體性能。
2)TiO2是寬禁帶半導(dǎo)體(≥3.0 eV),只能吸收紫外光,但紫外光只占太陽(yáng)光總能量的5%[77]。在催化過(guò)程中,TiO2產(chǎn)生的光生電子和空穴極易復(fù)合,這大大降低了TiO2的催化性能[78]。目前關(guān)于改性TiO2、使TiO2能在自然光下發(fā)揮光催化的研究較多[79-84],但大部分研究是將改性后的TiO2直接作為涂層達(dá)到防腐防污的目的,將它作為填料的研究卻極少。
針對(duì)以上問(wèn)題,作以下幾點(diǎn)展望。
1)為進(jìn)一步改善納米TiO2在環(huán)氧樹(shù)脂中的分散性,可通過(guò)類(lèi)似硅烷偶聯(lián)劑的其他化學(xué)物質(zhì)(飽和脂肪酸A)對(duì)納米TiO2進(jìn)行改性,降低納米TiO2的表面能,采用機(jī)械攪拌和超聲結(jié)合技術(shù)等物理法將TiO2分散在環(huán)氧樹(shù)脂中,破壞團(tuán)簇的納米TiO2之間的范德華力和雙電層靜電作用力[85],提高TiO2與環(huán)氧樹(shù)脂的空間斥力位能[86],從而改善納米TiO2在環(huán)氧樹(shù)脂中的分散性,進(jìn)一步提高復(fù)合材料的性能。
2)將納米TiO2與窄禁帶、上轉(zhuǎn)換及長(zhǎng)余輝等半導(dǎo)體材料復(fù)合,擴(kuò)大它們對(duì)自然光的響應(yīng)范圍,提高自然光的利用率,同時(shí)降低光生電子和空穴復(fù)合的概率,提高TiO2光催化性能,將復(fù)合半導(dǎo)體材料作為納米填料加入環(huán)氧樹(shù)脂中,提高環(huán)氧樹(shù)脂的性能,拓展環(huán)氧樹(shù)脂的應(yīng)用領(lǐng)域。
3)可對(duì)納米TiO2進(jìn)行表面功能化改性,將改性后的納米TiO2添加到環(huán)氧樹(shù)脂中制備超疏水功能材料,或先將環(huán)氧樹(shù)脂進(jìn)行改性得到超疏水環(huán)氧樹(shù)脂后,再將超疏水TiO2與之復(fù)合得到超疏水功能材料。利用復(fù)合材料的超疏水性,提高復(fù)合材料的防腐、防污、自清潔等性能。
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Research Progress in Preparation Technology and Properties of Nano-TiO2Modified Epoxy Resin
1,2,1,1,2,1,2
(1. Northeastern University, Shenyang 110819, China; 2. Army Academy of Armored Forces, Beijing 100072, China)
Epoxy resin is a thermosetting material with excellent property, which has a wide range of application in the such fields as aerospace, petrochemical, naval, marine because of its good anti-corrosion, thermal stability and mechanical properties. However, epoxy resin has a high cross-linking density, which makes epoxy resin toughness poor and its applications limited. Therefore, the preparation of high-property epoxy resin has become a research hotspot. The preparation technology of nano-TiO2modified epoxy resin is summarized, including mechanical stirring method, ultrasonic method, mechanical stirring and ultrasonic bonding method, bead milling method and chemical-physical bonding method. Mean, the principle of each preparation technology and the influence of each preparation technology on the dispersibility of nano-TiO2in epoxy resin and the existing deficiencies are also summarized. Adding nano-fillers is one of the effective methods to improve the properties of epoxy resin which can achieve the purpose of filling, leveling, protecting and insulating the substrate. In order to enhance the properties and broaden the applications of epoxy resin, epoxy resin which was modified by nano-TiO2has a good application prospect. The preparation technology of TiO2modified epoxy resin includes mechanical stirring method, ultrasonic method, mechanical and ultrasonic combination method, bead milling method and chemical and physical combination method are summarized, and the principle of each preparation technique is also summarized. Focusing on the dispersion of nano-TiO2in epoxy resin which play a important role in improving the properties of TiO2/EP nanocomposites. Although all methods can disperse nano-TiO2in epoxy resin effectively, the dispersion mechanism is different which divided into physics dispersion and chemical dispersion, physics dispersion is main disperse nano-TiO2in epoxy resin by physical means, chemical dispersion can solve the compatibility of nano-TiO2and epoxy resin. The related properties of epoxy resin modified by TiO2have been improved, and mechanical property, corrosion resistant property, antifouling property, and weather resistance property are briefly reviewed with emphasis. The mechanical properties of epoxy resin can be improved when TiO2is grafted with epoxy resin to improve the structure of epoxy resin when filling in nano-TiO2. In addition,the filling of TiO2can effectively improve the density, lower surface energy and enhance corrosion resistance of the epoxy resin. The anti-fouling performance and weatherability of epoxy resin is improved on account of taking advantage of TiO2photocatalytic performance and ultraviolet light absorption performance. To conclude, this paper prospects the future research directions of TiO2/EP nanocomposites.
epoxy resin; nano-TiO2; composites; the preparation technology; properties; TiO2/EP
TB332
A
1001-3660(2022)07-0011-16
10.16490/j.cnki.issn.1001-3660.2022.07.002
2021–06–15;
2021–11–02
2021-06-15;
2021-11-02
國(guó)家自然科學(xué)基金(51905543);國(guó)防科技卓越青年科學(xué)基金(2017–JCJQ–ZQ–001);中國(guó)博士后科學(xué)基金(2018M643857)
The National Natural Science Foundation of China (51905543); National Defense Science and Technology Outstanding Youth Science Foundation (2017-JCJQ-ZQ-001); China Postdoctoral Science Foundation (2018M643857)
萬(wàn)濤(1994—),男,博士研究生,主要研究方向?yàn)楸砻婀こ獭?/p>
WAN Tao (1994-), Male, Doctoral candidate, Research focus: surface engineering.
魏世丞(1974—),男,博士,教授,主要研究方向?yàn)楸砻婀こ毯驮僦圃旃こ獭?/p>
WEI Shi-cheng (1974-), Male, Doctor, Professor, Research focus: surface engineering and remanufacturing engineering.
萬(wàn)濤, 王博, 韓慶, 等. 納米TiO2改性環(huán)氧樹(shù)脂的制備技術(shù)與性能研究進(jìn)展[J]. 表面技術(shù), 2022, 51(7): 11-26.
WAN Tao, WANG Bo, HAN Qing, et al. Research Progress in Preparation Technology and Properties of Nano-TiO2Modified Epoxy Resin[J]. Surface Technology, 2022, 51(7): 11-26.
責(zé)任編輯:蔣紅晨