聚乳酸扩链改性及其挤出发泡的研究

采用扩链剂对聚乳酸（PLA）进行扩链改性,研究了扩链剂对PLA流变性能的影响。采用3种不同类型的化学发泡剂：发泡剂A（发泡母粒）、发泡剂B\[自制复合发泡剂：偶氮二甲酰胺（AC发泡剂）/碳酸氢钠(NaHCO3)\]、发泡剂C(自制改性AC发泡剂),利用单螺杆挤出机对PLA进行挤出发泡。采用扫描电子显微镜观察分析了发泡材料的断面泡孔结构。结果表明,加入扩链剂可有效提高PLA的熔体强度和黏度及降低其熔体流动速率,改善PLA的发泡效果,扩链剂含量为0.8份（质量分数,下同）时,发泡材料的发泡效果最好;实验所用的3种发泡剂中,发泡剂C的发泡效果最好,发泡剂含量为1.5份时,发泡样品的表观密度较小（0.6 g/cm3）,泡孔直径最小(约为57 μm),泡孔密度最大（约为7.69×10^6个/cm3）,泡孔分布均匀,无明显泡孔破裂和连通现象。     

增容作用对聚乳酸/高密度聚乙烯合金发泡行为的影响

以乙烯甲基丙烯酸缩水甘油酯共聚物（GEMA）为增容剂,采用熔融共混法制备了聚乳酸（PLA）/高密度聚乙烯（PE-HD）增容合金。以CO2为发泡剂进行釜压发泡,制备出PLA/PE-HD增容合金泡沫。结果表明,加入GEMA后,聚合物合金的结晶能力有所下降和流变性能略有提高;随着GEMA含量的增加,PE-HD分散相尺寸减小,数量增多,聚合物合金发泡样品的泡孔结构可以实现从复合泡孔到单一泡孔的转变。     

PBAT的扩链反应及其微孔发泡行为研究

以己二酸丁二醇酯-对苯二甲酸丁二醇酯（PBAT）共聚物为基体,加入不同含量的扩链剂,经熔融共混后,制备扩链PBAT。结果表明,随着扩链剂含量的增加,熔融混合的扭矩值、凝胶含量和结晶温度逐渐升高,熔融温度基本不变,结晶度下降,黏弹性得到改善;以超临界CO2为物理发泡剂,通过间歇式釜压发泡法制备微孔PBAT泡沫,随着扩链剂含量的增多,发泡样品的泡孔尺寸变小,泡孔密度逐渐增加,当扩链剂的份数为0.8时,泡孔尺寸为4.4 μm,泡孔密度为1.65×1010个/cm3。     

聚丙烯物理法微孔发泡操作条件与泡孔形态的关系研究

以超临界CO2流体和丁烷为发泡剂,用快速释压的方法,对PP的微孔发泡进行了研究,得到了泡孔密度达10^9泡孔／cm^2,泡孔直径为20-50μm的微孔泡沫塑料颗粒。研究表明,改变饱和压力和温度可以控制发泡的泡孔结构和密度。使用CO2为发泡剂,当温度低于90℃或压力低于6．0MPa时,PP很难出现发泡。提高温度使泡孔出现五边形的结构但泡孔尺寸增大;增加饱和压力,泡孔密度增加,泡孔直径减小。用超临界CO2流体和丁烷作发泡剂时所得到的泡孔密度分别为2．0×10^8-10^9和2．0×10^5—10^7泡孔／cm^3,泡孔平均尺寸分别为20—50μm和100—500μm。用超临界CO2流体和丁烷混合气体作为发泡剂时泡孔直径则出现了双峰分布的结构;加入成核剂炭黑后所得到的泡孔尺寸大于未加成核剂的情况,其泡孔密度和泡孔直径分别为7．0×10^6—1．6×10^9泡孔／cm^3和55—300μm。     

扩链PBS的微孔发泡行为研究

以聚丁二酸丁二醇酯（PBS）为基体,加入不同含量的扩链剂,通过熔融共混法制备扩链PBS样品。随后以超临界CO₂作为物理发泡剂,通过釜压发泡法在87 ℃下对PBS进行物理发泡。结果表明,随着扩链剂含量的增加,PBS的结晶温度先升高后略微下降,结晶度略微提高,黏弹性改善;随着扩链剂含量的增加,泡孔尺寸和发泡倍率逐渐减小,泡孔密度逐渐增加;当扩链剂含量为8 %（质量分数,下同）时制备的扩链PBS微孔泡沫的泡孔尺寸为9.2 μm,泡孔密度为1.93×10⁹ 个/cm³。     

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。     

赤泥对聚乳酸热性能、力学性能和发泡行为的影响研究

通过熔融共混法制备了二苯基甲烷二异氰酸酯（MDI）改性的聚乳酸/赤泥（PLA/RM）复合材料,并利用超临界CO₂固相发泡法对复合材料进行发泡,采用差示扫描量热仪、万能试验机和固相发泡法对复合材料的结晶行为、力学性能和发泡行为进行了研究。结果表明,RM对PLA具有促进结晶的效果,结晶度由5.34 %提高至13.89 %;RM含量对材料的泡孔参数具有明显控制作用;当加入5 %（质量分数,下同）的RM时,发泡材料的泡孔密度降低至1.82×10⁷ 个/cm³,发泡倍率达到2.25倍,当RM为3 %时添加MDI时,泡孔密度由3.28×10⁷个/cm³提高到12.46×10⁷个/cm³,发泡倍率由2.26倍提高到12.40倍;RM和MDI协同作用对PLA泡沫的泡孔形态和力学性能具有显著的调控作用。     

聚醚砜超临界CO2发泡行为研究

以超临界CO₂为发泡剂,采用间歇发泡法制备了聚醚砜（PES）泡沫。采用旋转流变仪和扫描电子显微镜分析表征了PES发泡的均相成核行为,继而分别以滑石粉和二氧化硅（SiO₂）作为异相成核剂,探究了PES发泡过程中的异相成核行为。结果表明,间歇发泡法制备PES泡沫的发泡区间为200~230 ℃;最佳浸泡压力为20 MPa;最佳浸泡时间为3 h;未改性PES的泡孔直径均可在10 μm以下,泡孔密度在10⁹~10¹⁰ 个/cm³之间,但泡孔壁较厚;SiO₂相对于Talc,表现出更显著的异相成核作用;在210 ℃、3 h、20 MPa的发泡条件下,添加0.9 %（质量分数,下同）的SiO₂,可得到泡孔直径为0.77 μm,泡孔密度为7.14×10¹¹ 个/cm³的PES微孔泡沫。     

PS/PLA共混物的相态结构及其发泡行为研究

采用密炼机制备了聚苯乙烯/聚乳酸(PS/PLA)共混物,以超临界二氧化碳(CO2)为物理发泡剂,采用釜压法制备了PS/PLA共混物泡沫。采用差示扫描量热仪、偏光显微镜和扫描电子显微镜研究了PLA等温结晶行为、PS/PLA共混物的相态结构和PS/PLA共混物泡沫的泡孔结构。结果表明,反应型增容剂使PLA的等温结晶速率提高,晶体尺寸降低;增容剂能够促进PLA在PS中的分散;PLA的加入在发泡过程中能够起到异相成核作用,PLA的结晶有利于气泡的增长和稳定。     

高熔体弹性PLA/咖啡渣复合材料的发泡行为研究

通过熔融共混法制备二苯基甲烷二异氰酸酯（MDI）改性的聚乳酸（PLA）/咖啡渣复合材料,利用超临界CO2对复合材料进行发泡,并对复合材料的流变性能、热性能、力学性能及发泡行为进行了研究。结果表明,MDI与PLA发生扩链反应,PLA/咖啡渣复合材料的熔体弹性、热性能和力学性能均显著提高;MDI能促进诱导冷结晶和熔融双峰形成,使复合材料的冷结晶度提高至24.68 %;加入MDI后,PLA/咖啡渣复合材料的泡孔密度和发泡倍率明显提高;在诱导冷结晶的温度下发泡,PLA/咖啡渣复合材料的泡孔密度和发泡倍率分别达到9.26×106 个/cm3和9.33倍。     

结晶特性对微发泡聚丙烯材料发泡行为的影响

以化学发泡注塑成型技术为主线,在二次开模条件下制备微发泡PP材料;通过DSC、XRD技术分析了结晶特性对微发泡聚丙烯材料发泡行为的影响。结果表明:结晶特性对气泡的成核、长大和定型过程具有明显的影响;添加滑石粉的改性PP材料结晶特性较差,发泡质量明显降低,泡孔直径和泡孔密度分别为36.98μm、3.29×107个/cm3;添加云母粉的改性PP材料具有合适的结晶温度和结晶度,发泡质量较理想,泡孔直径和泡孔密度分别为22.09μm、4.76×108个/cm3;能够获得泡孔细小、均匀的微发泡PP材料。     

Effect of poly(butylenes succinate) on the microcellular foaming of polylactide using supercritical carbon dioxide

Microcellular Polylactide (PLA) and PLA/poly(butylenes succinate) (PBS) foams were prepared by batch foaming process with supercritical carbon dioxide. The introduced PBS phase was immiscible with the PLA matrix and separated as domains. The study of CO₂ solubility in PLA and PLA/PBS blends indicated the addition of PBS decreased the gas solubility due to the poor affinity of CO₂ for PBS. The crystallization behavior of PLA was enhanced by small amount of PBS with lower cold crystallization temperature and higher crystallinity. However, separated PBS droplets led to less perfect and small crystallites, which showed greatly effect for the PLA foaming process. The investigation on the foaming conditions dependence indicated the PLA/PBS blends required higher temperature and longer time for the cell growth, which were nucleated around the interface between PLA and PBS. With less CO₂ content in the PLA or PLA/PBS blends after different desorption time, the final cell morphology exhibited more uniform size distribution with bigger average cell size and smaller cell density. Different from the well closed-cell structure for neat PLA foam, the PLA/PBS foam presented open cell structure due to the cell nucleation around the PLA/PBS interface and the lower melt strength of PBS phase.     

Foamability and viscosity behavior of extrusion foamed PLA–pulp fiber biocomposites

This study addresses the effect of fiber reinforcement, chain extension, and physical foaming agent type on foam morphology and viscosity behavior of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. PLA reinforced with 0, 10, and 20 wt % of bleached kraft pulp fibers with and without chain extender were foamed using two different physical foaming agents (carbon dioxide and isobutane) by extrusion foaming. Densities, foam morphologies, and viscosities were systematically analyzed and compared from the produced foams. As a conclusion, low-density foams are produced with both foaming agents and fiber levels, fiber addition limiting cell growth. Isobutane provides better dimensional stability with narrower cell size distribution, whereas carbon dioxide enables lower foaming temperature. Chain extension is essential to achieve foam with low density and good cell structure. Contrary to nonchain extended PLA, addition of fibers reduced the viscosity of chain extended PLA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48202.     

Extrusion Foaming of Poly (lactic acid)/Soy Protein Concentrate Blends

Poly(lactic acid) (PLA) and soy protein concentrate (SPC) were compounded using poly(2‐ethyl‐2‐oxazoline) as compatibilizer by twin‐screw extrusion, and the resulting blends were foamed by a chemical blowing agent (CBA) using the same extruder. Effects of foaming temperature and CBA content on cell density and foam density were investigated. Polymeric methylene diphenyl diisocyanate (pMDI) as a co‐compatibilizer was added prior to foaming extrusion and its effects on foam morphology and properties were also studied. The results showed that cell density and foam density were greatly influenced by foaming temperature and CBA content. Using the strong interfacial modifier pMDI in PLA/SPC blends resulted in high‐cell density and low‐foam density when CBA concentration was low.

     

纳米SiO_2对微发泡聚丙烯复合材料发泡行为的影响

将改性的纳米二氧化(硅SiO2)以不同含量加入到聚丙(烯PP)中,在二次开模条件下制备微发泡PP/纳米SiO2复合材料,分析了纳米SiO2含量对微发泡复合材料发泡行为的影响。结果表明:随着纳米SiO2含量的增加,复合材料的平均泡孔直径减小,泡孔密度增加,当纳米SiO2含量为4%时,复合材料的泡孔直径为16.3μm泡,孔密度达1.41×109个/cm3具,有理想的发泡效果。     

聚乳酸微纳复合泡孔的结构与性能研究

通过熔融共混制备聚乳酸（PLA）/聚（己二酸丁二酯?对苯二甲酸丁二酯）（PBAT）共混物。以环氧扩链剂（CE）为相容剂,研究了CE含量对共混物的流变行为、结晶行为的影响,并研究了CE含量为5份的共混物在冷结晶温度下的发泡行为以及泡沫的拉伸性能。结果表明,共混体系的相容性、结晶速率随着CE含量的增加而增加、可发性提高,在添加了5份CE的共混物中得到了微纳复合泡孔,泡孔密度达到10¹³ 个/cm³,相对于PLA泡沫,共混物泡沫的断裂伸长率提高了40 %。     

工艺参数对铁尾矿制备泡沫玻璃性能的影响

以铁尾矿为主要原料、CaCO3和Na2CO3为发泡剂、Na3PO4×12H2O和硼砂(Na2B4O7×10H2O)为稳定剂,制备了性能良好的泡沫玻璃材料,并研究了工艺参数对制品性能的影响. 结果表明,CaCO3为主要发泡剂,Na2CO3含量对制品性能影响不大;Na3PO4×12H2O为主要稳定剂,Na2B4O7×10H2O含量不宜过多;发泡温度升高使制品孔径变大、容重和抗压强度降低;而烧结温度升高使制品的容重和抗压强度均先减小后增大. 制备泡沫玻璃适宜的工艺参数为(%, w)：基础玻璃84, CaCO3 3, Na2CO3 2, Na3PO4×12H2O 8, Na2B4O7×10H2O 3, 发泡温度900~950℃,烧结温度1100℃. 由此制得的泡沫玻璃材料容重约为2.05 g/cm3,抗压强度达62 MPa左右.     

Physical extruder foaming of poly(lactic acid)—processing and foam properties

The article describes extrusion foaming of poly(lactic acid) (PLA) using carbon dioxide in the supercritical state as foaming agent emphasizing the steps required to establish a stable extrusion process. Low melt strength of PLA plays a role in optimizing processing conditions. The tests included PLA grades of different viscosity in addition to a chain extender. Processing at low temperature is possible due to the plasticizing effect of the CO₂ on the PLA melt and a sufficiently low melt temperature is also a prerequisite in production of stable foams due to improved melt strength. Foams were characterized by density, cell structure, crystallinity, and mechanical properties in compression. Low density, microcellular foams with density down to 20–30 kg/m³ were obtained for three different PLA grades. Varying die temperature and pressure drop rate we can explain observed abrupt drops in density with increasing CO₂ content by the interplay between cell nucleation and gas diffusivity at given temperatures. An effect on melt strength similar to using a chain extender is achieved by lowering the melt temperature at the die. Observed variations in sample crystallinity do not correlate with foam density. The PLA foams have good energy absorption capability. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers