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。     

聚乳酸/纳米蒙脱土纳米复合材料的制备与挤出发泡研究

采用熔融插层法制备了聚乳酸/有机改性纳米蒙脱土（PLA/OMMT）复合材料,对其复合结构、力学性能、热性能、动态流变性能进行了测试和表征,并研究了复合材料的挤出发泡行为。结果表明,不同含量的OMMT与PLA进行熔融插层会形成不同的插层与剥离结构;3 %的OMMT可以提高PLA的力学性能、改善热性能;OMMT能够提升PLA的熔体强度,同时在挤出发泡过程中起到成核剂的作用,并且能够减弱发泡剂气体向PLA熔体外部的扩散,从而提高PLA挤出发泡的效果。     

热塑性聚酰胺弹性体的扩链反应及发泡行为研究

采用环氧型扩链剂KL-E4370对热塑性聚酰胺弹性体（TPAE）进行了扩链改性,通过旋转流变仪、差示扫描量热仪（DSC）和扫描电子显微镜（SEM）等对扩链前后TPAE的流变性能、结晶性能和发泡性能进行了表征,并研探讨了扩链反应的机理。结果表明,TPAE的熔体黏弹性较差,可发性差;加入扩链剂能够有效提高TPAE的支化程度;通过对TPAE进行扩链改性可使其复数黏度增加一个数量级以上,提高熔体黏弹性,从而增大发泡倍率,拓宽发泡温区,改善泡孔破裂及合并问题;但扩链后TPAE的结晶性能下降,起始结晶温度降低20 ℃左右,使得泡孔收缩情况明显;扩链剂含量为1 %（质量分数,下同）的TPAE泡沫的发泡倍率从纯TPAE的5.5倍增加到了约9倍,泡孔直径达50 μm。     

扩链剂对聚对苯二甲酸乙二醇酯流变性能和发泡性能影响

采用均苯四甲酸酐（PMDA）作为聚对苯二甲酸乙二醇酯(PET)的扩链剂制备了扩链改性PET（CEPET）,并以超临界二氧化碳(CO2)为物理发泡剂,采用釜压法制备了CEPET泡沫;通过旋转流变仪和扫描电子显微镜研究了CEPET的流变性能和CEPET泡沫的泡孔结构。结果表明,随着PMDA含量的增加,CEPET试样的储能模量逐渐增加,损耗因子逐渐降低,CEPET的熔体强度明显高于纯PET;CEPET泡沫的泡孔形态得到改善,发泡倍率得到提高;加入1.0 份（质量份,下同）扩链剂时,发泡倍率能够达到32.55倍。     

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 ℃。     

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。     

扩链改性对聚乳酸挤出吹膜成型的影响

利用扩链剂改性聚乳酸(PLA),然后用改性PLA进行吹膜成型,研究了扩链剂用量对PLA熔体流动性、膜泡稳定性及薄膜力学性能的影响。结果表明:扩链剂的加入使PLA的熔体流动速率(MFR)明显下降,同时使其黏度增加,且提高了膜泡的稳定性;当扩链剂用量为0.5%、0.6%时,PLA薄膜的拉伸强度显著提高,最大冲击强度较纯PLA提高了74.67%。     

增容剂种类对熔融共混法制备PLA/PBAT体系的影响

采用熔融共混法制备了不同增容剂体系的聚乳酸/聚己二酸-对苯二甲酸-丁二酯共聚物(PLA/PBAT)共混熔体,系统地研究了采用扩链剂SW04、环氧扩链剂XY-4370以及扩链剂Joncryl作为增容剂改性的PLA/PBAT体系。并对他们的熔体流动速率、力学性能以及热性能进行检测。对比实际挤出实验过程中熔体的情况,使用扩链剂Joncryl作为增容剂的体系熔体更均匀,明显改善挤出胀大现象,对PLA/PBAT体系的增容效果更好。且使用扩链剂Joncryl作为增容剂的熔体稳定性更好,综合力学性能也更佳。     

PLA发泡——使用熔体强度增强剂通过化学发泡剂生产低密度泡沫材料

本文的目的主要是说明提高丙烯酸熔体强度增强剂的用量对聚乳酸(PLA)自由发泡泡沫挤出性能和相应的加工稳定性和孔结构的影响。另一个目标是证明使用丙烯酸熔体强度增强剂改性PLA时,均衡的发泡剂母料对于开发质量优异的低密度泡沫的有效性,以及对自由泡沫挤出制品的孔结构和表面质量的影响。1机理丙烯酸熔体强度增强剂通过链缠结过程来提     

可生物降解聚乳酸发泡材料研究进展

综述了聚乳酸(PLA)发泡材料在包装领域、汽车领域和生物医疗领域的多种应用现状,概括了釜压发泡法、连续挤出发泡法、注塑发泡法以及其他发泡成型法制备PLA发泡材料的成型机理及泡孔结构特点,重点介绍了分子链结构改性、共混改性和微米/纳米级填充改性等较为有效的PLA改性方法,以及各种改性方法所制备的PLA发泡材料的泡孔形态特征。     

聚乳酸增韧改性研究

通过熔融共混法制备了通用注塑级聚乳酸(PLA)材料,研究了刚性粒子种类,增韧剂种类和协同增韧等对PLA力学性能的影响,同时通过控制扩链剂的添加量有效地对注塑级PLA的熔体流动速率(MFR)进行控制。结果表明:协同增韧剂对PLA有较好的增韧效果,冲击强度从3.5 kJ/m2提高到15 kJ/m2,是单一增韧剂的2.5倍。通过引入扩链剂,得到一系列不同MFR的注塑级PLA材料,满足不同的工业化产品需求。     

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.     

Effect of molding conditions on crystallization kinetics and mechanical properties of poly(lactic acid)

Although Poly(lactic acid) (PLA) possesses many desirable properties, above all biodegradability, its heat deflection temperature is too low for many desirable applications. Similarly, to any other polymers, also for PLA the physical and mechanical properties in the solid state depend on the morphology and crystallinity degree, which in their turn are determined by the thermomechanical history experienced during solidification. A large crystallinity degree is highly desirable to increase the heat resistance of PLA but is rather difficult to reach during injection molding due to the very slow crystallization kinetics of this material. In this work, the crystallization kinetics of an injection molded PLA grade was assessed in function of the thermal history by using calorimetric analysis. The cold crystallization kinetics (starting from the amorphous glassy sample) turned out to be faster than melt crystallization kinetics. Following the indications gained from crystallization kinetics, some samples were injection molded imposing different thermal histories. The effect of molding conditions on crystallinity was determined. This finding was adopted to develop a post‐molding stage which allows obtaining crystalline samples in times much shorter (of a factor about two) with respect to samples injection molded in a hot mold kept at temperatures close to the maximum crystallization rate. POLYM. ENG. SCI., 57:306–311, 2017. © 2016 Society of Plastics Engineers     

Effects of the chain‐extender content on the structure and performance of poly(lactic acid)–poly(butylene succinate)–microcrystalline cellulose composites

Composites of poly(lactic acid) (PLA) with poly(butylene succinate) (PBS) and microcrystalline cellulose (MCC) as reinforcements of the polymer matrix were prepared by melt blending to improve the brittleness of PLA. As a reactive compatibilizer, a chain extender was used in an attempt to solve the composites’ interfacial problems and to improve their mechanical properties; Fourier transform infrared spectroscopy indicated that the chain extender functionally reacted with PLA, PBS, and MCC mainly through end carboxyls or end hydroxyls. Scanning electron microscopy indicated that the chain extender significantly improved the cohesive interfacial forces. Differential scanning calorimetry and X‐ray diffraction showed that the chain extender inhibited crystallization, and these effects were greater when its percentage was increased. The addition of chain extender improved the tensile and impact strength of the composites, and this improvement was proportional to the chain‐extender percentage. However, the elongation at break decreased when the chain‐extender percentage was over 0.5% because of mild crosslinking within the resin matrix. Rheology indicated that the complex viscosity and storage and loss moduli of the composites increased with increasing amount of chain extender; this indicated that the addition of chain extender improved the melt strength and processability of the composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44895.     

Engineered poly(lactic acid)‐talc biocomposites for melt processing: Effects of co‐blending with poly(butylene succinate) and poly(butylene terephthalate) on thermal and mechanical behavior

This article deals with the design and manufacturing of a novel class of PLA‐based material specifically engineered for injection molding, suitable for food contact and characterized by a good balance of mechanical properties and thermal resistance. A commercial PLA grade was modified by blending it with microlamellar talc as reinforcing filler, poly(butylene succinate) (PBS), and poly(butylene terephthalate) (PBT) as secondary polymeric phases. Ternary blend/talc biocomposites were achieved. The different constituents of the biocomposites were compatibilized by reactive compounding extrusion using maleic anhydride (MAH) grafted PLA (PLA‐MA). The thermal properties of the compounds prior and after injection molding were characterized by differential scanning calorimetry. The mechanical response of the injection molded materials was evaluated by flat indentation and flexural tests. The mechanical properties of the PLA/talc‐based biocomposites and crystallinity of PLA can be controlled by fine tuning the blend by the addition of PBS and PBT in the formulation. In particular, biocomposites characterized by good strength and toughness can be obtained by injection molding, without affecting thermal stability. Based on the experimental findings, the PLA‐based formulations pose; therefore, solid bases for replacing oil‐based plastics in several markets, specifically in the segment of food and pharmaceutical packaging. POLYM. ENG. SCI., 59:264–273, 2019. © 2018 Society of Plastics Engineers     

Effect of a chain extender on the rheological and mechanical properties of biodegradable poly(lactic acid)/poly[(butylene succinate)‐co‐adipate] blends

Biodegradable polymer blends based on poly(lactic acid) (PLA) and poly[(butylene succinate)‐co‐adipate] (PBSA) were prepared with a laboratory internal mixer. An epoxy‐based, multifunctional chain extender was used to enhance the melt strength of the blends. The morphology of the blends was observed with field emission scanning electron microscopy. The elongational viscosities of the blends, with and without chain extender, were measured with a Sentmanat extensional rheometer universal testing platform. The blends with chain extender exhibited strong strain‐hardening behavior, whereas the blends without chain extender exhibited only weak strain‐hardening behavior. Measurements of the linear viscoelastic properties of the melts suggested that the chain extender promoted the development of chain branching. The results show that PBSA contributed to significant improvements in the ductility of the PLA/PBSA blends, whereas the chain extender did not have a significant effect on the elastic modulus and strain at break of the blends. The combined blending of PLA with PBSA and the incorporation of the chain extender imparted both ductility and melt strength to the system. Thus, such an approach yields a system with enhanced performance and processability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

PETG连续挤出发泡行为

采用环氧型扩链剂对苯二甲酸-乙二醇-1,4-环己烷二甲醇共聚酯(PETG)进行熔融扩链,并利用高级扩展流变仪、熔体强度测定仪和扫描电子显微镜分别进行了剪切流变、拉伸流变测试和连续挤出发泡行为研究。结果表明:扩链后PETG的储能模量、损耗模量、复数黏度随扩链剂含量的增加而增大,而其损耗因子随扩链剂含量的增加而减小;扩链剂的加入能有效提高PETG树脂的熔体强度和改善其"可发泡性",在发泡成型过程中可以有效阻止泡孔的塌陷和破裂,进而形成泡孔尺寸和形态分布较为均匀的制品。     

Recyclability Studies on Poly(lactic acid)/Poly(butylene succinate-co-adipate) (PLA/PBSA) Biobased and Biodegradable Films

Poly(lactic acid)/poly(butylene succinate-co-adipate) (PLA/PBSA) blends are found promising for film packaging applications because of their flexibility, resistance, and compostability. Industrially extruded granules and films based on PLA and containing different amounts of PBSA are reprocessed through mini-extrusion, to simulate recycling, and tested in terms of their melt flow rate as a function of PBSA content. Moreover, pure PLA commercial granules and the film produced extruding the PLA/PBSA 60/40 blend are reprocessed several times by injection molding and characterized in terms of melt flow rate, mechanical properties, thermal properties, and color as a function of injection molding cycles. The variation in melt fluidity and thermo-mechanical properties is negligible up to 3 injection molding cycles for both pure PLA granules and PLA/PBSA blend. In the case of blend the change in color (yellowing and darkening) is more evident and slight local compositional change in injection molded items can be evidenced as well as a slight decrease in PBS crystallinity as a function of injection molding cycles. Nevertheless, in applications where these aspects are not critical, these materials can be recycled by extrusion or injection molding before being composted, thus prolonging their life cycle and storing carbon in them as longer as possible.