发泡工艺对超临界CO_2/PLA微孔发泡泡孔形态的影响

研究了超临界CO2/PLA微孔发泡过程中,发泡温度、饱和压力、剪切速率对聚合物PLA泡孔形态的影响。结果表明,发泡温度对泡孔形态影响很大,温度降低,熔体强度增加,泡孔塌陷和合并减少,发泡材料的泡孔密度增大,泡孔尺寸减小,但温度太低时,熔体黏度和表面张力增加,发泡样品泡孔密度较低,泡孔壁较厚;压力对发泡形态的影响也是很显著的,压力太低,CO2的溶解度小,泡孔壁厚,泡孔分布不均匀。随着压力升高,CO2的溶解度增加,发泡样品的泡孔密度增加,泡孔更加均匀;随着转子转速增加,泡孔尺寸减小,气泡成核密度增大。但是转子转速过快,泡孔沿剪切的方向被拉长,泡孔取向严重,泡体质量变差。     

PBT含量对PLA/PBT原位微纤复合材料流变及发泡性能的影响

聚乳酸(PLA)是用量最大的可生物降解材料之一,由于其拉伸流变性能较差,难于发泡。本文采用聚合物微纳层叠共挤装置制备PLA/聚对苯二甲酸丁二醇酯(PBT)原位微纤复合材料(PLA/PBT-MRC),研究了PLA/PBT-MRC的微纤形态、熔体的动态流变性能和拉伸流变性能。PLA、PLA/PBT-MRC注塑发泡后的泡孔形貌、注塑发泡制品的拉伸、缺口冲击和弯曲力学性能。研究表明：PLA/PBT-MRC中微纤宽度低至0.72μm,宽度随PBT含量增加而增大;随PBT含量增加PLA/PBT-MRC的储能模量、损耗模量和复数黏度都增大;PBT含量增加可以明显改善PLA熔体的拉伸流变性能,相对PLA表现出明显的拉伸应变硬化;PLA/PBT-MRC注塑发泡后泡孔直径比PLA注塑发泡泡孔直径减小800%,泡孔密度增加600%,发泡制品的拉伸强度、缺口冲击强度、弯曲强度分别提高22.2%、10.1%和26.4%。     

双螺杆挤出制备低密度聚乳酸微孔泡沫塑料

通过构建双螺杆挤出发泡系统、降低发泡温度和加入交联剂来制备低密度聚乳酸微孔泡沫塑料。结果表明:降低发泡温度有利于聚乳酸泡沫密度的降低。交联剂的含量应适中,以获得合适的熔体强度,利于泡孔成核和泡孔长大。当发泡温度为125℃,交联剂含量为0.2份时,制备的PLA泡沫的体积膨胀系数达到39倍。     

发泡聚乳酸流变性能及泡孔结构的研究

采用偶氮二甲酰胺（AC）做为发泡剂，直接通过挤出过程制备聚乳酸（PLA）泡沫塑料，通过显微镜照片、HAKKE流变仪观察和研究了工艺条件对其泡孔结构的影响。结果表明，发泡剂与成核剂的增加能降低发泡PLA的表观密度，增加其泡孔密度。流变试验表明纯PLA与发泡PLA熔体在低剪切速率下都呈现剪切变稀现象，发泡后PLA熔体的黏度会下降10％～30％。发泡剂含量在4％以下时，泡孔直径随发泡剂含量增加而减小；发泡剂含量增加到5％及以上时，PLA熔体强度过小，泡孔会过于密集而导致塌陷和串泡。成核剂的加入能够明显降低PLA熔体强度，异相成核使得泡孔直径较均相成核大，但前者泡孔密度较后者小。     

EVM/PLA共混发泡材料泡孔结构和性能的研究

以乙烯-醋酸乙烯酯橡胶(EVM)和聚乳酸(PLA)共混物为基体材料,经模压发泡制备了共混发泡材料。研究了EVM/PLA不同共混比、硫化剂(DCP)、发泡剂(AC)和白炭黑用量以及不同发泡时间对EVM/PLA共混物发泡材料泡孔结构和物理机械性能的影响。结果表明,随PLA组分的减少,白炭黑和DCP用量的增加,泡孔逐渐减小,均匀度增加,孔壁增厚,材料的密度、拉伸强度和拉断伸长率呈升高趋势,发泡倍率呈降低趋势。随发泡剂AC用量的增加,泡孔壁变薄,平均泡孔尺寸变化不大,材料的密度、拉伸强度和拉断伸长率呈降低趋势,发泡倍率增加。随硫化时间的延长,泡孔尺寸变小,孔壁增厚、发泡倍率逐渐下降,拉伸强度先增大后减少,拉断伸长率先下降后上升。     

丙烯酸酯橡胶/聚乳酸发泡材料的结构与性能

以偶氮二甲酰胺(AC)为发泡剂制备了丙烯酸酯橡胶(ACM)/聚乳酸(PLA)发泡材料,考察了ACM/PLA(质量比)和AC用量对发泡材料结构与性能的影响。结果表明,随着PLA并用比的增加,发泡材料的泡孔密度减小,泡孔逐渐变大,泡孔壁变薄,邵尔C硬度增大,撕裂强度和拉伸强度均降低,耐老化性能得到改善;随着AC用量的增加,发泡材料的泡孔壁变薄,大泡孔数增加,泡孔大小均匀度降低,密度、邵尔C硬度、拉伸强度和撕裂强度均逐渐降低,并且下降幅度逐渐变小,耐老化性能没有明显变化;发泡材料的压缩应力-应变变化包括较宽的线弹性区域、较窄的泡孔塌陷平台和泡孔壁相互接触后的密实化区域3个阶段。     

三官能环氧树脂在聚乳酸交联挤出发泡中的应用

将三官能团环氧树脂作为交联剂用于聚乳酸（PLA）的挤出化学发泡成型,研究了三官能环氧树脂含量对PLA熔融结晶性能、交联度、熔体强度的影响以及对PLA化学挤出发泡试样的泡孔形态的影响。结果表明,随着三官能环氧树脂含量的增加,冷结晶温度提高,且添加三官能环氧树脂后熔融峰由单峰变成双峰,结晶峰面积、熔融峰面积以及结晶度都是先增加后减少的趋势;PLA体系的交联度和熔体强度的显著提高随着三官能团环氧树脂的增加;PLA体系泡孔破裂减少,开孔率减少,泡孔尺寸先减小后增大;较佳挤出机头温度为170~175 ℃。     

PBS/木粉复合发泡材料的制备及性能研究

采用模压化学发泡的方法并添加过氧化二异丙苯、交联助剂三羟甲基丙烷三甲基丙烯酸酯和木粉成功制备了聚丁二酸丁二酯(PBS)/木粉复合发泡材料,并对其性能进行了研究。结果表明,交联剂和木粉的加入能够有效提高PBS的储能模量、损耗模量以及熔体黏度,且流变性能随木粉含量增加而呈升高趋势;所制备的发泡材料均为闭孔结构,且泡孔大小较为均匀;随着木粉含量的增加,发泡材料的拉伸强度先升高后降低,但变化幅度较小,密度逐渐增大,而比拉伸强度、断裂伸长率和发泡倍率逐渐降低。木粉的含量为30份时仍能制备泡孔相对均匀的PBS/木粉复合发泡材料,其密度为0.33 g/cm3,且拉伸强度与未加木粉时相差不大。     

聚乳酸挤出发泡特性研究

使用过氧化二异丙苯(DCP)交联聚乳酸以提高它的熔体强度,采用单螺杆挤出机制备了聚乳酸发泡材料.使用转矩流变仪研究了不同DCP含量PLA交联体系的流变性能;通过DSC测试研究了纯PLA及交联PLA体系的熔融以及结晶过程;同时研究了发泡试样的泡孔结构.结果表明,DCP对PLA有交联和促进降解的作用,并促进了PLA的均相成核,但对改善PLA结晶性能没有很明显的作用.PLA交联之后,熔体强度有一定提高,在DCP含量为2.5份时发泡效果最好.     

不同熔体强度对聚乳酸微发泡行为的影响

合适的熔体强度是取得良好发泡效果的关键。通过对熔体强度的聚乳酸(PLA)进行微发泡注射实验,对其发泡密度、泡孔尺寸及分布情况及常规力学性能进行了测试和表征。实验结果表明:不同的熔体强度会对聚乳酸的发泡行为产生不同的影响,熔融指数在11.2 g/10min时,得到PLA发泡制品最低密度值为0.0928 g/cm~3,平均泡孔直径为38.5μm,泡孔密度为2.08×106个/cm~2;随着熔体强度的降低,PLA发泡制品的平均泡孔直径先增大后减小,泡孔密度先减小后增大,PLA发泡制品的发泡密度值和常规力学性能呈现先减小后增大的变化趋势。对熔融指数为11.2 g/10min的PLA进行微发泡后具有良好的泡孔结构和综合力学性能。     

Foaming behaviour and cell structure of poly(lactic acid) after various modifications

Improving the melt strength of poly(lactic acid) (PLA) is of continuing strategic research interest since a low melt strength results in poor processability of foaming and blowing film. PLA was modified in various ways including crosslinking, chain extension, grafting, blending, plasticizing and nucleation to improve its melt strength. This work focuses on the effect of melt strength after various modifications on foaming behaviour and cell structures of PLA foam. Cell density was increased and cell structure became more uniform with increasing melt strength, in particular when the melt strain was also increased after modification. With increasing melt strength the phenomenon of open and ruptured cells was decreased. The foaming window was widened with increasing melt strength, in particular after crosslinking, chain extension and blending with elastomer. Molecular weight, thermal properties and viscosity of PLA after various modifications were also studied and used to explain the foaming behaviour and foam structures. Copyright © 2012 Society of Chemical Industry     

Reactively Modified Poly(lactic acid): Properties and Foam Processing

Summary: In order to produce modified poly(lactic acid) (PLA) resins for applications requiring high melt viscosity and elasticity (e.g., low‐density foaming, thermoforming), a commercial PLA product has been reactively modified in melt by sequentially adding 1,4‐butanediol and 1,4‐butane diisocyanate as low‐molecular‐weight chain extenders. By varying amounts of the two chain extenders associated to the end group contents of PLA, three resulted samples were obtained. They were then structurally characterized by FTIR spectroscopy and molecular structure analysis. Their thermal, dynamic mechanical thermal properties and melt viscoelastic properties were investigated and compared along with unmodified PLA. The results indicated that chemical modification may be characterized as chain scission, extension, crosslinking, or any combination of the three depending on the chain extender amounts. The increase of PLA molecular weight could be obtained by properly controlling amounts of two chain extenders. The samples with increased molecular weights showed enhanced melt viscosity and elasticity. Such property improvements promised a successful application for modified PLA in a batch foam processing by producing foams with reduced cell size, increased cell density and lowered bulk foam density in comparison with plain PLA foam.

Cellular morphology of a modified PLA foam.     

Cell coalescence suppressed by crosslinking structure in polypropylene microcellular foaming

A series of crosslinked polypropylene samples with increased melt strengths were prepared via a copolymerization reaction, followed by melt processing. These crosslinked PP samples (PP‐Cs) were foamed by a temperature rising process using supercritical CO₂ as the physical blowing agent. The introduction of crosslinking structure resulted in PP‐Cs foams with well‐defined closed cell structure, decreased cell size, and increased cell density in comparison with a linear PP, which were attributed to the suppressed cell coalescence due to the significant increase in melt strength of PP‐Cs. Further increasing the crosslinking degree tended to enhance the suppression effect on the cell coalescence, and hence increase the cell density of PP foams under the same foaming conditions, especially at the longer foaming times. The well‐defined closed cell structure was observed at the foaming temperature of 170–250°C and saturation pressure of 12–20 MPa. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

热塑挤出制备无机阻燃聚乙烯醇泡沫材料及其影响因素的研究

以水为增塑剂兼物理发泡剂,氢氧化铝(ATH)为无机阻燃剂兼异相成核剂,通过热塑挤出方法制备了无机阻燃聚乙烯醇/氢氧化铝(PVAL/ATH)复合泡沫材料,采用扫描电子显微镜(SEM)等研究了水和ATH含量、口模温度、螺杆转速、交联剂对复合泡沫材料泡孔结构的影响。结果表明,适当的口模温度和螺杆转速是实现体系中水的可控、连续、稳定发泡的关键因素,适量添加的阻燃剂能够起到良好异相成核剂的作用,在最佳工艺条件下,当PVAL/ATH/水为100/80/30,口模温度为125℃,螺杆转速为30 r/min时,制备得到综合性能优异的无机阻燃PVAL/ATH泡沫材料,泡沫材料的表观密度为0.32 g/cm3,膨胀倍率为10.0,泡孔密度约为1.6×105个/cm3。此外,引入硼酸作为交联剂,有效提高了熔体强度并改善了泡孔结构,交联后泡沫材料的拉伸强度和断裂伸长率分别提高到6.3 MPa和59.2%。     

Microcellular foaming of poly(lactic acid) branched with food-grade chain extenders

This study evaluated the effectiveness and efficiency of two food-grade multifunctional epoxies chain extenders (CE) in branching PLA and improving its foamability. Both CE grades were effective in branching PLA causing increased end mixing torque, shear, elongational viscosities, molecular weight but decreased crystallinity of poly(lactic acid) (PLA) with CE content, due to chain entanglements. CE with low epoxy equivalent weight (EEW) was more efficient than the counterpart with high EEW due to its high reactivity. Neat PLA foams showed poor cell morphology with areas without nucleated cells and had a low expansion, owing to its low elongational viscosity. By contrast, there was a considerable change in the morphology of the PLA foam structure caused by its branching. Chain-extended PLA foams had uniform cell morphology with a high void fraction (up to ~85%) and expansion ratio (an eightfold expansion over unfoamed PLA) due to their high elongational viscosities, suggesting that melt properties of branched PLA were appropriate for optimum cell growth and stabilization during foaming. Overall, CE with low EEW was the most effective grade and 0.25% the optimum content that provided appropriate melt viscosity to produce PLA foams with a homogeneous structure, fine cells, high void fraction, high volume expansion ratio, and cell-population density.     

Properties of a poly(L‐lactic acid)/poly(D‐lactic acid) stereocomplex and the stereocomplex crosslinked with triallyl isocyanurate by irradiation

A poly(L ‐lactic acid) (PLLA)/poly(D ‐lactic acid) (PDLA) stereocomplex was prepared from an equimolar mixture of commercial‐grade PLLA and PDLA by melt processing for the first time. Crosslinked samples were obtained by the radiation‐induced crosslinking of the poly(lactic acid) (PLA) stereocomplex mixed with triallyl isocyanurate (TAIC). The PLA stereocomplex and its crosslinked samples were characterized by their gel behavior, thermal and mechanical measurements, and enzymatic degradation. The crosslinking density of the crosslinked stereocomplex was described as the gel fraction, which increased with the TAIC content and radiation dose. The maximum crosslinking density was obtained in crosslinked samples of PLA/3% TAIC and PLA/5% TAIC irradiated at doses higher than 30 kGy. The stable crosslinking networks that formed in the irradiated PLA/TAIC substantially suppressed the segmental mobility for the crystallization of single crystals as well as stereocomplex crystals. The crosslinking network also significantly improved the mechanical properties and inhibited the enzymatic degradation of crosslinked PLA/3% TAIC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

辐照改性聚丙烯拉伸流变行为及其挤出发泡的研究

通过在线形聚丙烯中加入双官能团丙烯酸酯类单体,经小剂量γ射线高能辐照,制备了高熔体强度聚丙烯,研究了其拉伸流变行为及其在挤出发泡方面的应用。Rheotens拉伸流变测试表明,辐照改性后由于形成了长支化分子结构,聚丙烯的熔体强度、拉伸黏度显著提高,具有明显的应变硬化特征。实验表明,ZnO可明显降低AC发泡剂分解温度,缓和分解放热;在辐照改性制备的高熔体强度聚丙烯中加入AC／ZnO复合发泡剂,可挤出发泡得到泡孔尺寸较为均一、分布均匀、具有闭孔结构的发泡材料。     

辐照改性制备长支链型高熔体强度聚丙烯流变性能(Ⅱ)拉伸流变

通过辐照法制备了长支链型高熔体强度聚丙烯(LCB-HMSPP),采用Rheotens熔体拉伸流变仪研究了辐照改性PP的熔体强度和拉伸流变行为,讨论了敏化剂含量、辐照剂量、高分子量物质和温度对PP拉伸流变行为的影响。研究结果表明：PP的熔体强度、拉伸应力、拉伸黏度等拉伸流变物理量随敏化剂增加而显著增强,并随辐照剂量呈先上升后下降的趋势,辐照剂量为5kGy时,熔体强度和拉伸黏度到达最大。添加极少量高分子量物质(UHMWPE)也能有效提高PP的熔体强度。LCB-HMSPP的熔体强度活化能显著降低,熔体强度温度敏感性下降,可在较宽的温度范围内表现出较高的熔体强度。     

The application of blocked polyfunctional isocyanate as a cross-linking agent in biodegradable extruded poly(lactic acid) foam

A polyfunctional isocyanate was prepared and was blocked by methanol to limit its premature reactivity with water or other nucleophiles. The methanol-blocked polyfunctional isocyanate was used as a cross-linking agent to improve the melt strength and foamability of poly(lactic acid) (PLA). The effect of the blocked polyfunctional isocyanate (BPI) content on the melting behavior, crystallization, degree of cross-linking, and melt strength of PLA was investigated, and the cellular morphologies of the PLA foams obtained by chemical foaming extrusion were studied, as well. The cold crystallization temperature increased with increasing BPI proportion and the melting peak changed from a single to multiple peaks upon the addition of BPI to PLA. The ∆H_c, ∆H_m, and X_c values initially increased and then decreased with increasing BPI content. It can be attributed to the effect of cross-linking on crystallization behavior of PLA. The degree of cross-linking increased with the BPI content of the PLA mixtures. The melt strength of the PLA mixture increased with increasing proportions of BPI, whose incorporation led to a decrease in the void fraction, cell size, and open cell content of the PLA foams but an increase in the cell density. When BPI was added to the PLA, the cell morphologies of the PLA mixtures were obviously enhanced.