姬洪 宋明根 張玥 陳康 張玉梅
摘 要:為了紡制兼具良好阻燃與力學(xué)性能的共聚型阻燃聚酯工業(yè)絲,在分析高分子量阻燃共聚酯流變特性以及量化不同紡絲溫度條件下共聚酯熱降解程度的基礎(chǔ)上,設(shè)計(jì)和優(yōu)化熔融紡絲工藝。對(duì)紡制的阻燃工業(yè)絲力學(xué)性能與阻燃性能進(jìn)行測(cè)試,并采用X-射線衍射和聲速纖維取向測(cè)量儀對(duì)纖維的微細(xì)結(jié)構(gòu)進(jìn)行測(cè)試分析。結(jié)果表明:相較純PET,共聚酯熔體黏度較低,溫敏性更為明顯。采用低的紡絲溫度(285 ℃左右),熔體黏度對(duì)紡絲壓力影響小且熱降解程度低,可制備斷裂強(qiáng)度為6.75 cN/dtex、極限氧指數(shù)(LOI)可達(dá)31%的共聚型阻燃聚酯工業(yè)絲,且其阻燃耐久性突出,實(shí)現(xiàn)了良好阻燃性能與力學(xué)性能共聚型阻燃聚酯工業(yè)絲的制備。
關(guān)鍵詞:聚酯工業(yè)絲;共聚型;阻燃;力學(xué)性能
中圖分類號(hào):TS102
文獻(xiàn)標(biāo)志碼:A
文章編號(hào):1009-265X(2023)04-0056-07
收稿日期:2022-11-24
網(wǎng)絡(luò)出版日期:2023-02-22
基金項(xiàng)目:高性能纖維及制品教育部重點(diǎn)實(shí)驗(yàn)室開放課題(2020)
作者簡介:姬洪(1987—),男,山東泰安人,博士,主要從事高性能纖維材料開發(fā)與應(yīng)用方面的研究。
通信作者:張玉梅,E-mail:zhangym@dhu.edu.cn
(Mn>2.5X104,[η]>0.85 dL/g)聚對(duì)苯二甲酸乙二醇酯(PET)制備的聚酯工業(yè)絲具有強(qiáng)度高、模量大、耐熱性能好等優(yōu)點(diǎn)[1],廣泛用于安全帶、吊裝帶、土工布、汽車簾子線、纜繩、傳送帶等領(lǐng)域[2-3]。但是,PET的極限氧指數(shù)(LOI)只有20%左右,在纖維燃燒性能等級(jí)劃分中屬于易燃等級(jí),限制了其應(yīng)用領(lǐng)域的進(jìn)一步拓展[4-6]。通過聚合反應(yīng)將阻燃單體共聚引入聚酯大分子鏈,可以有效避免阻燃劑在聚酯加工及使用過程中的遷移,與共混添加法相比具有阻燃耐久等優(yōu)點(diǎn),是制備阻燃聚酯纖維材料的一種較為理想的方法[7-8]。
采用共聚法制備阻燃聚酯工業(yè)絲的技術(shù)要求高,由于共聚單體空間位阻、大分子鏈規(guī)整性破壞以及弱鍵等原因,阻燃共聚酯在固相縮聚反應(yīng)(SSP)中分子量提升[9]以及在紡絲加工過程中高分子量共聚酯的分子量保持是制備共聚型阻燃聚酯工業(yè)絲的關(guān)鍵技術(shù)。PET在高溫加工條件下會(huì)發(fā)生降解反應(yīng),嚴(yán)重影響制品性能與品質(zhì)[10]。阻燃共聚酯因阻燃單體的引入,其鍵接結(jié)構(gòu)發(fā)生改變,相較于常規(guī)PET可能更易發(fā)生熱解[11-13]。現(xiàn)有共聚型阻燃聚酯工業(yè)絲產(chǎn)品其力學(xué)性能與阻燃性能難以兼顧 (斷裂度6.5 cN/dtex左右,LOI在30%以下),遠(yuǎn)不能滿足特殊的工業(yè)應(yīng)用領(lǐng)域,如用于水龍帶、過濾/通風(fēng)織物和涂層織物等的特定要求[15]。目前高分子量阻燃共聚酯在熔融紡絲過程中的熱降解及工藝調(diào)控的相關(guān)信息未見報(bào)道,然而,這對(duì)于其熱解控制、分子量的保持具有重要意義。另一方面,聚合物熔體流變特性是熔融紡絲加工中的關(guān)鍵參數(shù),不僅受共聚阻燃劑的影響,同時(shí)分子量參數(shù)的微小變化也會(huì)導(dǎo)致其流變特性行為的顯著變化。因此為保證紡絲順利進(jìn)行以及成纖力學(xué)性能,需要對(duì)這些材料特性指標(biāo)予以明確,為相應(yīng)的工藝提供參數(shù)指導(dǎo)。
在以往研究阻燃共聚酯SSP反應(yīng)并成功制備高分子量共聚酯的基礎(chǔ)上[9],本文首先研究紡絲熔融加工條件下高分子量阻燃共聚酯的流變行為,并對(duì)紡絲工藝進(jìn)行相應(yīng)設(shè)計(jì),對(duì)紡絲成型過程中共聚酯的熱降解程度進(jìn)行明確,據(jù)此優(yōu)化紡絲工藝,最后對(duì)制備的工業(yè)絲的性能與結(jié)構(gòu)進(jìn)行測(cè)試、表征和分析。
1 實(shí) 驗(yàn)
1.1 實(shí)驗(yàn)材料
高分子量聚酯(HPET,特性黏度為(1.050±0.003) dL/g)和高分子量阻燃共聚酯(HFRP,特性黏度為(1.050±0.005) dL/g),均由浙江尤夫高新纖維股份有限公司提供,阻燃共聚酯所采用的阻燃劑為2-羧乙基苯基次磷酸(CEPPA),共聚酯的磷含量為0.006%。
1.2 紡絲試驗(yàn)
以HPET和HFRP為原料,采用紡絲-后牽伸兩步法制備聚酯工業(yè)絲(P-Y)和阻燃聚酯工業(yè)絲(FRP-Y),設(shè)計(jì)單纖纖度為5 dtex。
熔融紡絲工藝:采用日本ABE公司紡絲機(jī)進(jìn)行紡絲試驗(yàn),其中噴絲板規(guī)格為:孔徑為5 mm,孔數(shù)為36孔。紡絲試驗(yàn)中螺桿(一區(qū)到四區(qū))、管道、計(jì)量泵以及箱體溫度設(shè)置如表1所示。熔體由噴絲板擠出后,經(jīng)側(cè)吹冷卻,通過紡絲甬道后由卷繞機(jī)卷繞成筒,卷繞速度為800 m/min。
后牽伸工藝:采用平行牽伸機(jī)(蘇州特發(fā)機(jī)電有限公司,TF-100)對(duì)熔紡低速卷繞的初生絲進(jìn)行牽伸。其中工藝參數(shù)為: 熱盤溫度為80 ℃;熱板溫度為160 ℃,牽伸倍數(shù)分別為3.2,3.8,4.2,4.6。
熱管牽伸工藝:采用有機(jī)高性能纖維溫控多級(jí)牽伸實(shí)驗(yàn)裝置(實(shí)驗(yàn)室自制裝置)對(duì)平板牽伸倍率為3.2倍的纖維進(jìn)行三級(jí)熱管牽伸,P-Y和FRP-Y兩種樣品的熱牽伸溫度如表2所示,總后牽伸倍率為5.8倍。
1.3 測(cè)試與表征
1.3.1 特性黏度
參照標(biāo)準(zhǔn)GB/T 14190-2017《纖維級(jí)聚酯切片(PET)試驗(yàn)方法》,將干燥充分的樣品溶解于苯酚/1,1,2,2-四氯乙烷(50/50,質(zhì)量比)混合溶劑,溶液濃度為0.50 g/dL。在恒溫水浴槽中,溫度(25±0.05) ℃下使用毛細(xì)管直徑0.7~0.8 mm的烏氏黏度計(jì)進(jìn)行特性黏度測(cè)定。
1.3.2 燃燒性能測(cè)試
LOI值 (極限氧指數(shù))測(cè)試中將50根紗線加捻,捻度約20捻/10 cm,制成長約10 cm的繩狀樣條,參考JIS L1091—1999《阻燃測(cè)試E-1法》進(jìn)行測(cè)試;垂直燃燒試驗(yàn)采用極限氧指數(shù)(LOI)樣條制備方法制備待測(cè)樣品,參照GB/T 2408—2021 《塑料 燃燒性能的測(cè)定 水平法和垂直法》進(jìn)行燃燒測(cè)試。
1.3.3 X-射線衍射實(shí)驗(yàn)(XRD)
采用日本理學(xué)公司的D/max-2550VB+/PC 型18 kW轉(zhuǎn)靶 X 射線衍射儀進(jìn)行XRD測(cè)試。樣品制成粉末狀,以消除測(cè)試過程中取向?qū)ρ苌鋸?qiáng)度的影響。將剪碎后的樣品置于樣品臺(tái)上進(jìn)行測(cè)試,其中X射線波長為0.154 nm, 2θ測(cè)試范圍為 5°~60°。
1.3.4 聲速取向
采用東華凱利公司的SCY-Ⅲ型聲速取向測(cè)試儀,測(cè)定聲波在纖維中的傳播速率,計(jì)算纖維的聲速取向因子fs。
1.3.5 熔體流變性能測(cè)試
將樣品120 ℃干燥12 h,含水率低于6×10-5%,采用奧地利安東帕有限公司Physica MCR301旋轉(zhuǎn)流變儀,選取等溫恒定剪切速率時(shí)間掃描測(cè)試模式,25 mm平行板,間距1 mm,剪切速率5 s-1,測(cè)試時(shí)間0~1800 s。
1.3.6 纖維力學(xué)性能測(cè)試
采用YG 020B 形單紗強(qiáng)力測(cè)試儀,在恒溫恒濕環(huán)境下(20 ℃/65% RH)對(duì)纖維力學(xué)性能進(jìn)行測(cè)試,其中測(cè)試參數(shù)設(shè)定:強(qiáng)力測(cè)試加持距離200 mm,拉伸速度200 mm/min。
2 結(jié)果與討論
2.1 熔體流變特性
由圖1可知,兩種樣品熔體黏度,隨著溫度的增加,發(fā)生了明顯降低。而兩種樣品通過對(duì)比可以發(fā)現(xiàn),在相同溫度條件下,HFRP的熔體黏度顯著較低,這說明共聚改變了聚酯大分子鏈段結(jié)構(gòu),從而導(dǎo)致了熔體黏度變化。鏈段“躍遷”需要一個(gè)最小的能量(流動(dòng)活化能△E)才可以由原位置躍遷至附近的空穴,阻燃共聚酯具有較高流動(dòng)活化能△E,因此在流變測(cè)試結(jié)中顯示,其黏度變化對(duì)溫度表現(xiàn)出較高的敏感性,溫度升高,其熔體黏度急劇下降。
熔體變稀雖然能夠從一定程度上降低板前壓力增加流動(dòng)性,但也會(huì)引起熔體強(qiáng)度劣化,特別是出噴絲板后熔體的穩(wěn)定性有一定程度波動(dòng),因此適當(dāng)?shù)亟档腿垠w溫度,以提高熔體強(qiáng)度。由圖1可知,HFRP在溫度為285~275 ℃之間的熔體黏度與HPET在300 ℃左右的熔體溫度相近,組件壓力的公式(1) 估算表明FRPET此溫度區(qū)間的熔體板前壓力與HPET紡絲溫度時(shí)的板前壓力相比下降不到5%,不會(huì)發(fā)生較大波動(dòng),這有利于在生產(chǎn)過程中避免過多紡絲參數(shù)的調(diào)整。
2.2 紡絲穩(wěn)定性
在紡絲實(shí)驗(yàn)中,重點(diǎn)對(duì)紡絲溫度工藝參數(shù)進(jìn)行了細(xì)致探討。如表3不同紡絲溫度條件時(shí)阻燃聚酯特性黏度降結(jié)果所示,高分子量阻燃共聚酯分子量降低(特性黏度)與紡絲加工溫度密切相關(guān)。
在最高紡絲溫度305 ℃時(shí),特性黏度由1.05 dL/g降低至0.62 dL/g,黏度降高達(dá)40.3%。適當(dāng)降低紡絲溫度后,特性黏度降有所改善,在紡絲溫度為280 ℃左右時(shí),在保證紡絲壓力在穩(wěn)定范圍內(nèi)的前提下,此時(shí)特性黏度降在10.6%左右的較低水平,特性黏度可以維持在0.93 dL/g左右,基本滿足了工業(yè)絲對(duì)高分子量的要求。并基于此,對(duì)此溫度下熔紡卷繞成型的阻燃纖維進(jìn)行進(jìn)一步的牽伸加工處理。
為獲得更高強(qiáng)力,以滿足工業(yè)絲強(qiáng)力指標(biāo)要求,對(duì)低速卷繞獲得的初生絲進(jìn)一步進(jìn)行牽伸加工,以獲取更高取向與結(jié)晶度,達(dá)到較高強(qiáng)力。如表4不同牽伸倍率時(shí)阻燃聚酯工業(yè)絲力學(xué)性能測(cè)試結(jié)果所示,平板牽伸3.2~4.6倍時(shí),纖維強(qiáng)度隨著牽伸倍率的提高而增加明顯,斷裂伸長率隨之降低。P-Y與FRP-Y兩種樣品相比較,發(fā)現(xiàn)在相同牽伸倍率時(shí),后者強(qiáng)度始終低于P-Y樣品,但是其斷裂伸長較高。說明共聚結(jié)構(gòu)對(duì)纖維強(qiáng)度影響明顯,同時(shí)也賦予了纖維良好的可拉伸性。在平板牽伸最高倍率4.6倍時(shí),F(xiàn)RP-Y強(qiáng)度可以達(dá)到3.98 cN/dtex,為PET強(qiáng)度的87.8%,而此時(shí)的斷裂伸長率為21.2%,表明FRP-Y具有進(jìn)一步牽伸以提高強(qiáng)度的潛力。對(duì)此,為進(jìn)一步提高拉伸倍率,采用熱管牽伸工藝,最終在穩(wěn)定牽伸的情況下,最高倍率可以到達(dá)5.8倍,此時(shí)FRP-Y強(qiáng)度達(dá)到了6.75 cN/dtex (PET的強(qiáng)度為7.20 cN/dtex),實(shí)現(xiàn)了阻燃工業(yè)絲強(qiáng)度指標(biāo)要求。
2.3 阻燃聚酯工業(yè)絲的結(jié)構(gòu)
聚酯工業(yè)絲的優(yōu)異力學(xué)性能取決于其高結(jié)晶度、高取向度的微細(xì)結(jié)構(gòu)。對(duì)于阻燃聚酯工業(yè)絲微觀結(jié)構(gòu)進(jìn)行研究,一方面可以明確其結(jié)構(gòu)特征并與力學(xué)性能關(guān)聯(lián),探究其構(gòu)效關(guān)系;另一方面可以在明晰其結(jié)構(gòu)性能關(guān)系的基礎(chǔ)上,指明高強(qiáng)所需結(jié)構(gòu)特征的調(diào)控方向,為進(jìn)一步的工藝改進(jìn)具有指導(dǎo)意義。為此對(duì)所制備的強(qiáng)力最高的普通聚酯工業(yè)絲和阻燃聚酯工業(yè)絲的超分子結(jié)構(gòu)進(jìn)行表征。
P-Y與FRP-Y纖維的一維XRD曲線如圖2所示,可以看出兩種樣品的晶形結(jié)構(gòu)完全一致,說明共聚酯大分子鏈只有純聚酯鏈段才可以嵌入晶格。對(duì)其進(jìn)行進(jìn)一步數(shù)據(jù)處理,所得結(jié)構(gòu)參數(shù)如表5所示。由表中數(shù)據(jù)可以看出,F(xiàn)RP-Y纖維的結(jié)晶度明顯較低,且晶粒尺寸較下,這是由于共聚結(jié)構(gòu)對(duì)方大分子鏈規(guī)整性破壞所導(dǎo)致的。此外與P-Y纖維相比,F(xiàn)RP-Y纖維的整體取向(fS)微弱降低,晶區(qū)取向(fc)變化不大,但是非晶區(qū)取向(fA)較低。如圖3聚酯工業(yè)絲的結(jié)構(gòu)示意圖所示,阻燃共聚單元減少了純聚酯鏈段數(shù)量并且影響近端純聚酯鏈段長度不足難以嵌入晶格導(dǎo)致了超分子結(jié)構(gòu)參數(shù)中結(jié)晶度下降以及非晶區(qū)鏈段因共聚單元難以拉直取向度較低。
2.4 聚酯工業(yè)絲的阻燃性能
選取強(qiáng)力最高的聚酯工業(yè)絲樣品進(jìn)行燃燒性能測(cè)試結(jié)果如表6所示。阻燃聚酯工業(yè)絲實(shí)際磷含量測(cè)試結(jié)果為5.9×10-3%左右。極限氧指數(shù)(LOI)測(cè)試結(jié)果顯示,F(xiàn)RP-Y纖維樣品的LOI可以達(dá)到30.9%,表明其具有較好的阻燃性能。為了更全面地表征其燃燒性能,參照塑料測(cè)試標(biāo)準(zhǔn),對(duì)其垂直燃燒性能進(jìn)行了測(cè)試。其結(jié)果顯示,F(xiàn)RP-Y燃燒時(shí)間(2 s以內(nèi))明顯降低,且樣品損毀長度為0.7 cm,較P-Y樣品(8.1 cm)顯著改善。垂直燃燒實(shí)驗(yàn)中,F(xiàn)RP-Y表現(xiàn)為難點(diǎn)燃,良好的離火自熄性以及難續(xù)燃的優(yōu)異阻燃性。
3 結(jié) 論
阻燃共聚單元的引入可破壞大分子鏈規(guī)整性降低了熔體黏度,影響結(jié)晶,同時(shí)共聚弱鍵更易發(fā)生降解,基于此優(yōu)化設(shè)計(jì)了熱解可控的紡絲工藝,降低紡絲溫度、降低熱拉伸定型溫度與增
加定型時(shí)間,制得阻燃性能(LOI達(dá)30%以上)良好的阻燃聚酯工業(yè)絲,拉伸斷裂強(qiáng)度在6.75 cN/dtex左右,且水洗牢度性能優(yōu)異。與普通聚酯工業(yè)絲相比力學(xué)性能降低的原因是阻燃共聚結(jié)構(gòu)減少了可嵌入晶格鏈段數(shù)量,纖維結(jié)晶度和取向度降低。
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Spinning research of copolymerized flame-retardant polyester industrial yarns
JI Hong1, SONG Minggen1, ZHANG Yue2, CHEN Kang3, ZHANG Yumei2
(1.Zhejiang Unifull Industrial Fiber Co., Ltd., Huzhou 313017, China; 2a.College of Materials Science and Engineering;
2b. Key Laboratory of High Performance Fibers & Products, Ministry of Education, Donghua University, Shanghai 201620, China;
3.School of Materials Science and Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China)
Abstract:
Polyester industrial yarns are widely used in the fields of safety belts, rubber reinforcement materials, geotextile, and cables due to their excellent dimensional stability, weather resistance, and mechanical properties. However, the flammability of the polyester limits its further application. With excellent flame-retardant durability, the copolymerized flame-retardant polyester is the ideal method for the flame-retardant modification of polyester industrial yarns. In the process of high-temperature melt spinning, how to restrain the thermal degradation of high molecular weight copolyesters and ensure the appropriate liquidity of melt is the key technology to prepare the copolymerized flame-retardant polyester industrial yarns. Based on the rheological behavior of high molecular weight flame-retardant copolyesters during spinning and melting, the corresponding spinning process was designed, the thermal degradation degree of copolyesters during spinning and forming was determined, and the process parameters were optimized. Polyester industrial yarns with good mechanical properties, flame-retardant properties, and durability were prepared.
The rheological properties of high molecular weight flame-retardant copolyesters at different temperatures were tested by the rotating rheometer. The spinning processing temperature range was defined according to appropriate melt fluidity and stable spinning pressure requirements. At the same time, the thermal degradation of copolyesters was quantified at different spinning temperatures to optimize the melt-spinning process. Then, the thermal drawing processes such as temperature and ratio were designed to improve the mechanical properties of the fibers. The mechanical and flame-retardant properties of the industrial yarns were measured by means of tensile and combustion tests. In addition, X-ray diffraction and sonic orientation equipment were used to analyze and test the crystal and orientation of the fibers. It is found that compared with pure PET, the viscosity of copolyesters melt is lower and the temperature sensitivity is more obvious. When the temperature is between 275 ℃ and 285 ℃, the melt viscosity is similar to that of pure PET spinning temperature. The pressure fluctuation of the spinning pack in this temperature range is small, which is conducive to avoiding excessive adjustment of spinning parameters in the production process. The process was further optimized by choosing a lower spinning temperature (about 285 ℃). The melt viscosity had little influence on spinning pressure and the thermal degradation degree was low (the viscosity dropped to 11.5%). Finally, by multistage hot drawing process, the breaking strength of the flame-retardant industrial yarns prepared by the primary fiber can reach 6.75 cN/dtex, the limit oxygen index (LOI) can reach 31% and the flame-retardant durability is outstanding, which meets the requirements of flame-retardant and mechanical properties of flame-retardant polyester industrial yarns. The results of microstructure analysis show that the copolymerization unit reduces the number of pure polyester chain segments and results in a short length of near-end pure polyester chain segments, which makes it difficult to embed in the lattice and further leads to the decrease of crystallinity and the low orientation of the amorphous chain segment, and the decline of mechanical properties of flame retardant fibers.
Based on the rheological properties and degradation behavior of high molecular weight flame-retardant copolyesters, the key technical factors of processing and molding were studied. The melt spinning process was designed, the drawing parameters were optimized, and the relationship between structural characteristics and mechanical properties of the prepared flame-retardant copolyesters was analyzed. On this basis, the flame-retardant polyester industrial yarns with good mechanical properties and excellent flame-retardant properties and outstanding flame-retardant durability were prepared, which greatly expanded the application of polyester industrial yarns and had certain guiding significance for the development and application of flame-retardant polyester industrial yarns.
Keywords:
polyester industrial yarns; copolymerized; flame retardant; mechanical properties