分子結(jié)構(gòu)與交聯(lián)度對(duì)聚乙烯耐水樹枝老化特性影響的研究
發(fā)布時(shí)間：2018-11-15 12:38
【摘要】：在潮濕的環(huán)境下,水分子會(huì)在電場(chǎng)的作用下進(jìn)入電力電纜交聯(lián)聚乙烯絕緣中并逐漸形成水樹枝結(jié)構(gòu),水樹枝的存在不僅會(huì)劣化絕緣的機(jī)械和介電性能,而且長(zhǎng)期發(fā)展會(huì)形成電樹枝造成永久性破壞。因此,研究聚乙烯水樹枝老化的內(nèi)在機(jī)理對(duì)電力電纜的安全運(yùn)行十分重要。本文采用水刀電極法對(duì)試樣進(jìn)行加速水樹枝老化實(shí)驗(yàn),主要分為兩部分:(1)分子結(jié)構(gòu)對(duì)聚乙烯耐水樹枝老化能力的影響。試樣為主鏈帶有長(zhǎng)支鏈的LDPE、主鏈帶有大量短支鏈LLDPE和主鏈具有極少短支鏈的HDPE;(2)交聯(lián)度對(duì)聚乙烯耐水樹枝老化能力的影響。通過向聚乙烯基礎(chǔ)樹脂中加入不同含量的交聯(lián)劑得到不同交聯(lián)度的XLPE試樣。其中LDPE采用過氧化物交聯(lián)法,而LLDPE則采用新型的紫外光輻照交聯(lián)法。利用DSC對(duì)試樣的熔融-結(jié)晶曲線進(jìn)行測(cè)量、利用PLM和SEM對(duì)其球晶和片晶進(jìn)行觀測(cè)、并利用DMA和電子拉力機(jī)對(duì)試樣的動(dòng)態(tài)熱機(jī)械曲線和應(yīng)力-應(yīng)變曲線進(jìn)行測(cè)量。結(jié)合水樹枝的生長(zhǎng)機(jī)理,分別從聚乙烯的結(jié)晶形貌和片晶之間分子鏈的纏結(jié)兩種角度,解釋分子結(jié)構(gòu)和交聯(lián)度對(duì)聚乙烯耐水樹枝老化性能的影響機(jī)理。研究發(fā)現(xiàn):與LDPE和HDPE相比,LLDPE的耐水樹枝老化能力強(qiáng)。原因在于LLDPE密集的短支鏈分子結(jié)構(gòu),大量的短支鏈促進(jìn)了片晶之間的纏結(jié),水分子在LLDPE非晶相中需要更多的能量與時(shí)間來破壞這些纏結(jié)分子鏈,并且這些纏結(jié)分子鏈在一定程度上也會(huì)抑制片晶在水分子擠壓力下產(chǎn)生的滑移,這就相當(dāng)于削弱了電致應(yīng)力的破壞作用,抑制了水樹枝的生長(zhǎng)。從熔融-結(jié)晶曲線和PLM、SEM觀測(cè)結(jié)果可知,隨著試樣交聯(lián)度的升高,XLPE三維網(wǎng)狀結(jié)構(gòu)增強(qiáng),抑制了球晶和片晶的生長(zhǎng),使其結(jié)晶度下降,無定形區(qū)域面積增大,理論上會(huì)促進(jìn)水樹枝的生長(zhǎng),但交聯(lián)使其形成的三維網(wǎng)狀結(jié)構(gòu)限制了材料內(nèi)部水分沿電場(chǎng)方向發(fā)生形變擠壓材料形成水樹枝的能力。從實(shí)驗(yàn)結(jié)果可知,交聯(lián)形成的三維網(wǎng)狀結(jié)構(gòu)在提高材料耐水樹枝能力上起主導(dǎo)作用。從動(dòng)態(tài)熱機(jī)械曲線和應(yīng)力-應(yīng)變曲線可知,交聯(lián)度越高的XLPE,α松弛強(qiáng)度越弱,應(yīng)變硬化現(xiàn)象也越明顯。交聯(lián)鍵能夠有效加強(qiáng)非晶區(qū)分子鏈的纏結(jié)行為,在電致應(yīng)力應(yīng)力作用下的片晶之間的滑移與破壞變得更為困難,從而提高了抑制水樹枝生長(zhǎng)的能力。
[Abstract]:In humid environment, water molecules will enter the XLPE insulation of power cable under the action of electric field and form water tree structure gradually. The existence of water tree will not only deteriorate the mechanical and dielectric properties of insulation. And long-term development will form electric branches and cause permanent damage. Therefore, it is very important to study the inherent mechanism of polyethylene water tree aging for the safe operation of power cable. In this paper, the water knife electrode method is used to test the accelerated water tree aging of the sample, which is divided into two parts: (1) the effect of molecular structure on the aging resistance of polyethylene to water tree. The effects of crosslinking degree of HDPE; (2) on the aging resistance of LDPE, with long branched chain and HDPE; (2) with a large number of short branched chains on the aging resistance of polyethylene were investigated. XLPE samples with different crosslinking degree were obtained by adding different amount of crosslinking agent to PE base resin. The peroxide crosslinking method was used in LDPE and the new ultraviolet irradiation crosslinking method was used in LLDPE. The melt-crystallization curves of the samples were measured by DSC, the spherulites and tablets were observed by PLM and SEM, and the dynamic thermo-mechanical curves and stress-strain curves were measured by DMA and electronic tension machine. Based on the growth mechanism of water tree, the effects of molecular structure and crosslinking degree on the aging resistance of polyethylene were explained from the point of view of the crystalline morphology of polyethylene and the entanglement of molecular chains between sheets. It was found that compared with LDPE and HDPE, LLDPE had stronger water resistance to aging. The reason lies in the dense molecular structure of short branched chains of LLDPE. A large number of short branched chains promote the entanglement between wafers. Water molecules need more energy and time to destroy these entangled molecular chains in LLDPE amorphous phase. To some extent, these entangled molecular chains can also inhibit the slippage of lamellar crystals under water molecular extrusion pressure, which is equivalent to weakening the damage of electroinduced stress and inhibiting the growth of water branches. From the melting crystallization curve and PLM,SEM observation, it can be seen that with the increase of the cross-linking degree of the sample, the three-dimensional network structure of XLPE is enhanced, the growth of spherulites and tablets is inhibited, the crystallinity decreases, and the amorphous area increases. In theory it can promote the growth of water branches but the three-dimensional network structure formed by crosslinking limits the ability of the internal water to deform and extrude the materials along the direction of electric field to form water branches. From the experimental results, it can be seen that the three-dimensional network structure formed by cross-linking plays a leading role in improving the water-resistance of the materials. From the dynamic thermo-mechanical curves and stress-strain curves, it can be seen that the higher the crosslinking degree is, the weaker the relaxation strength of XLPE, 偽 is, the more obvious the strain hardening is. The cross-linking bond can effectively enhance the entanglement behavior of the molecular chains in the amorphous region, and the slip and destruction of the lamellae under the electrically induced stress becomes more difficult, thus improving the ability to inhibit the growth of water dendrites.
【學(xué)位授予單位】：哈爾濱理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM247
本文編號(hào)：2333323
[Abstract]:In humid environment, water molecules will enter the XLPE insulation of power cable under the action of electric field and form water tree structure gradually. The existence of water tree will not only deteriorate the mechanical and dielectric properties of insulation. And long-term development will form electric branches and cause permanent damage. Therefore, it is very important to study the inherent mechanism of polyethylene water tree aging for the safe operation of power cable. In this paper, the water knife electrode method is used to test the accelerated water tree aging of the sample, which is divided into two parts: (1) the effect of molecular structure on the aging resistance of polyethylene to water tree. The effects of crosslinking degree of HDPE; (2) on the aging resistance of LDPE, with long branched chain and HDPE; (2) with a large number of short branched chains on the aging resistance of polyethylene were investigated. XLPE samples with different crosslinking degree were obtained by adding different amount of crosslinking agent to PE base resin. The peroxide crosslinking method was used in LDPE and the new ultraviolet irradiation crosslinking method was used in LLDPE. The melt-crystallization curves of the samples were measured by DSC, the spherulites and tablets were observed by PLM and SEM, and the dynamic thermo-mechanical curves and stress-strain curves were measured by DMA and electronic tension machine. Based on the growth mechanism of water tree, the effects of molecular structure and crosslinking degree on the aging resistance of polyethylene were explained from the point of view of the crystalline morphology of polyethylene and the entanglement of molecular chains between sheets. It was found that compared with LDPE and HDPE, LLDPE had stronger water resistance to aging. The reason lies in the dense molecular structure of short branched chains of LLDPE. A large number of short branched chains promote the entanglement between wafers. Water molecules need more energy and time to destroy these entangled molecular chains in LLDPE amorphous phase. To some extent, these entangled molecular chains can also inhibit the slippage of lamellar crystals under water molecular extrusion pressure, which is equivalent to weakening the damage of electroinduced stress and inhibiting the growth of water branches. From the melting crystallization curve and PLM,SEM observation, it can be seen that with the increase of the cross-linking degree of the sample, the three-dimensional network structure of XLPE is enhanced, the growth of spherulites and tablets is inhibited, the crystallinity decreases, and the amorphous area increases. In theory it can promote the growth of water branches but the three-dimensional network structure formed by crosslinking limits the ability of the internal water to deform and extrude the materials along the direction of electric field to form water branches. From the experimental results, it can be seen that the three-dimensional network structure formed by cross-linking plays a leading role in improving the water-resistance of the materials. From the dynamic thermo-mechanical curves and stress-strain curves, it can be seen that the higher the crosslinking degree is, the weaker the relaxation strength of XLPE, 偽 is, the more obvious the strain hardening is. The cross-linking bond can effectively enhance the entanglement behavior of the molecular chains in the amorphous region, and the slip and destruction of the lamellae under the electrically induced stress becomes more difficult, thus improving the ability to inhibit the growth of water dendrites.
【學(xué)位授予單位】：哈爾濱理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM247
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