A look inside the extruder: evolution of chemistry,morphology and rheology along the extruder axis during reactive processing and blending

A simple device was recently developed for fast sampling (within a few seconds) of representative melt samples (about 2 g) on a running extruder. An array of such devices has been mounted on a twin‐screw extruder. The goal of this study was to de‐black‐box reactive processing of polymers by studying some typical examples. ‐ Processing of polyolefins in the presence of peroxides: when the polymer is molten and the melt temperature is sufficiently high branching/cross‐linking of PE and degradation of PP occurs; the conversion follows a convex profile along the screw axis, which profile is similar to the exponential profile calculated for peroxide decomposition. ‐ Free‐radical grafting of maleic anhydride (MA) onto polyolefins: MA grafting onto PE and PP also follows a convex profile with branching/cross‐linking as parallel side reaction for PE and degradation for PP; for PE degradation of the formed grafted/cross‐linked gel is observed at the end of the extruder. ‐ Reactive blending of PA‐6 with EPM‐g‐MA: within a few seconds the in‐situ compatibilization reaction, resulting in PA‐6/EPM graft copolymers, is completed and the degree of rubber dispersion has changed from the mm to the sub‐μm range, regardless of the MA content of EPM‐g‐MA and the EPM‐g‐MA content of the blend; PA degradation occurs along the whole extruder.     

Chemical and morphological evolution of PA‐6/Epm/Epm‐g‐MA blends in a twin screw extruder

Chemical conversion and morphological evolution of PA‐6/EPM/EPM‐g‐MA blends along a twin screw extruder were monitored by quickly collecting small samples from the melt at specific barrel locations. The results show that the MA content of all blends decreases drastically in the first zone of the extruder, i.e., upon melting of the blend components. Significant changes in morphology are also observed at this stage. A correlation between chemistry and morphology could thus be established. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1311–1320, 1999     

Stabilization and acidic dissolution mechanism of single-crystalline ZnO(0001) surfaces in electrolytes studied by in-situ AFM imaging and ex-situ LEED

A combined approach of pH-dependent in-situ AFM topography and ex-situ LEED studies of the stability and dissolution of single-crystalline ZnO(0001)-Zn surfaces in aqueous media is presented. Hydroxide-stabilized and single-crystalline ZnO(0001)-Zn surfaces turned out to be stable within a wide pH range between 11 and 4 around the point of zero charge of pH PZC = 8.7 +/- 0.2. Hydroxide stabilization turned out to be a very effective stabilization mechanism for polar oxide surfaces in electrolyte solutions. The dissolution of the oxide surface started at an acidic pH level of 5.5 and occurred selectively at the pre-existing step edges, which consist of nonpolar surfaces. In comparison, the oxide dissolution along the ZnO(0001) direction proved to be effectively inhibited above a pH value of 3.8. On the basis of these microscopic observations, the mechanistic understanding of the acidic dissolution process of ZnO could be supported. Moreover, both the in-situ AFM and the ex-situ LEED studies showed that the stabilization mechanism of the ZnO(0001) surfaces changes in acidic electrolytes. At pH values below 3.8, the hydroxide-stabilized surface is destabilized by dissolution of the well-ordered radical3. radical3. R30 hydroxide ad-layer as proven by LEED. Restabilization occurs and leads to the formation of triangular nanoterraces with a specific edge termination. However, below pH 4 the surface structure of the crystal itself is ill-defined on the macroscopic scale because preferable etching along crystal defects as dislocations into the bulk oxide results in very deep hexagonal etching pits.     

Influence of increasing zinc contents in brass in the early stages of corrosion investigated by in-situ TM-AFM and SIMS

In-situ tapping mode atomic force microscopy (TM-AFM), a powerful, high-resolution imaging technique for determining the structure of surfaces and ex-situ secondary ion mass spectroscopy (SIMS), a multielement, high-depth-resolution method, were used to examine the influence of increasing zinc contents in brass in the early stages of corrosion. Four different samples (pure Cu, pure Zn, Cu/Zn=90/10 wt% and Cu/Zn=70/30 wt%) were studied in order to determine their chemical behaviour under various atmospheric conditions. The in-situ TM-AFM investigations were carried out in synthetic air with 60% relative humidity (RH) and 80% RH with 250 ppb SO(2). The samples for the ex-situ SIMS experiments were weathered over a period of 60 h in 80% RH and 250 ppb SO(2). The in-situ TM-AFM investigations have shown that an increasing Zn content in brass increases the corrosion rate.     

化学增感对苯并三氮唑银的PTG材料感光性能的影响

本文主要研究了传统卤化银照相材料中的增感技术,如硫增感、金增感、硫加金协同增感,对新型的以苯并三氮唑银为银源、水性聚乙烯醇为粘合剂的光敏热成像材料增感是否有效的问题.结果显示,传统化学增感对异位法制备的溴化银为光敏剂的光敏热成像材料具有很好的增感效果,硫加金协同增感的效果要好于单独的硫增感和金增感;传统化学增感对原位法制备的溴化银为光敏剂的光敏热成像材料没有增感效果,反而减感,硫加金减感效果最严重.     

铝阳极氧化膜阻挡层的去除方法

多孔型铝阳极氧化膜常被用作制备纳米阵列材料的模板,然而阻挡层的存在却在很多方面制约了其应用.为此,已经提出了各种不同的方法来去除阻挡层.本文将这些方法分为2类,即剥离氧化膜去阻挡层和不剥离氧化膜去阻挡层.前者包括化学腐蚀法、干蚀法、电解剥离法;后者包括阶梯降压法、高电流击穿法、电化学法和有多孔铝支撑的化学溶解法.其中,化学腐蚀法和干蚀法的工艺条件已相当成熟,得到了广泛应用,而其它几种方法还多处于实验室研究阶段.由于氧化膜脆性很大,因此,不剥离氧化膜原位去除阻挡层的方法具有更大的实用价值.     

微型流化床反应分析仪中原位/非原位煤焦气化动力学研究

利用新开发的微型流化床反应分析仪(micro-fluidized bed reaction analysis, MFBRA) 考察了义马烟煤半焦的原位以及两种非原位半焦气化行为并测定了其动力学参数,其中,原位半焦气化是指煤热解温度和气氛与半焦气化过程一致,非原位半焦1气化是指煤在Ar气氛下热解,热态条件下直接在CO₂气氛下气化;非原位半焦2气化是指煤在Ar气氛下热解,冷却收集后再在CO₂气氛下气化。研究发现,原位半焦具有最大的比表面积和最小的平均孔径,石墨化程度最弱,且对CO₂的化学吸附能力最强,表面活性位点最多。在最小化气体扩散的实验条件下,原位半焦气化反应的反应速率明显比非原位半焦气化反应快,且求取的活化能数据较小。实验揭示了原位半焦和非原位半焦结构和反应性的差异,也证明了MFBRA对原位等温气化反应的适用性。     

聚甲基丙烯酸甲酯/苯乙烯-丙烯腈无规共聚物薄膜表面原位原子力显微镜相图

采用原位原子力显微镜在线跟踪方法,研究了聚甲基丙烯酸甲酯/苯乙烯 丙烯腈无规共聚物共混体系表面相分离行为,得到了具有下临界共溶温度（临界温度约为175 ℃）原位相图。 与文献报道的用离位方法所得结果的主要差别是原位的临界相分离温度稍有提高,以及离位结果中存在的组成对称性。 这些差别主要来源于离位和原位实验方法上的差别,薄膜厚度减小导致的相容性,热力学历史的变化以及基底效应的加剧。     

胜利褐煤半焦冷却处理对其微观结构及反应性能的影响

采用不同的冷却方式对胜利褐煤热解"热"半焦进行冷却处理,考查了冷却方式对半焦微观结构及反应性能的影响.利用特制两段新型石英反应器,在高纯氩气、400、600、800 ℃的条件下,对褐煤热解30 min制得的"热"焦,分别浸入室温、干冰及液氮环境中得到冷态半焦,然后在15%水蒸气、900 ℃、10 min的条件下对冷态半焦进行非原位气化反应.为了比较,同样热解条件下制得的"热"半焦不经冷却,通过直接切换反应气氛为15%水蒸气进行原位气化(气化条件与非原位气化相同).利用TGA、SEM、BET和Raman光谱仪对半焦反应性和微观结构进行表征和分析.结果表明,"热"焦的水蒸气原位气化半焦产率低于冷态半焦的非原位气化.冷却处理对半焦的孔结构影响较大,随着冷却速率的增大,半焦比表面积及总孔容积显著降低,但对半焦的化学结构(芳环体系和含氧官能团)的影响非常小.冷却速率越大,半焦的反应性越低,冷态半焦反应性能降低主要由于冷却对半焦孔结构造成的不可逆转的破坏.     

Studies on Mechanical Properties of Full-Biodegradable Starch-PVA-Polyester Films

A kind of full-biodegradable film material is discussed in this article.The film material is composed of starch,PVA,degradable polyesters(PHB,PHB-V,PCL) with built plasticizer,a cross-linking reinforcing agent and a wet strengthening agent.It contains a high percentage of starch.costs cheap and is excellent in weather fastness,temperature resistance and waterproof and it could be completely biodegraded.The present paper deals minly with a new technical route using a new type of electromagnetic dynamic blow molding extruder and some effects on mechanical properties of the system.     

Monitoring polyolefin modification along the axis of a twin‐screw extruder. II. Maleic anhydride grafting

The physico‐chemical phenomena developing along the screw axis of a twin‐screw extruder during the grafting of maleic anhydride (MA) onto polyolefins [polyethylene (PE), ethylene–propylene rubber (EPM), and polypropylene (PP)] were investigated. For this purpose, sampling devices located along the extruder barrel were used to collect polymer samples that were subsequently characterized to follow the degrees of grafting and crosslinking or degradation. A similar evolution of MA grafting was observed regardless of the polyolefin type or MA and peroxide concentration when grafting was performed under identical conditions, that is, the same peroxide type and set temperature. A correlation between the MA grafting and the calculated peroxide decomposition was established. Chemical reactions occurred along the extruder axis until the peroxide was fully converted. More detailed quantitative measurements of the peroxide decomposition and MA grafting would allow the development of accurate process models. The final MA content depended on the polyolefin composition (PE > EPM ≫ PP). As expected for PE, crosslinking occurred in addition to grafting, but after a certain residence time, the PE network degraded. The PP viscosity reduction after MA grafting was due to the conversion of tertiary PP radicals into primary PP radicals after grafting. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3919–3932, 2000     

STM investigation of the photoisomerization of an azobis-(benzo-15-crown-5) molecule and its self-assembly on Au(111)

Scanning tunneling microscopy (STM) has been employed to investigate the photoisomerization of azobis-(benzo-15-crown-5) on Au(111). A self-assembled monolayer of azobis-(benzo-15-crown-5) with a (3 x 7) symmetry was observed on Au(111). After ex-situ UV-light irradiation, a new adlayer structure with a different molecular arrangement could be seen on Au(111), although the domain size of the ordered packing is small. On the basis of a high-resolution STM image and photochemical reaction result, schematic models have been proposed for the original and ex-situ irradiated adlayers. After in-situ UV-light irradiation, the ordered arrays disappeared and many bright clusters emerged at domain boundaries. The results presented here provide direct evidence at the molecular level for a photochemical reaction.     

XPS Characterization of Carbon Nanotube Supported CoMo Hydrodesulfurization Catalysts

In this paper, the effect of catalytic support and sulfiding method on the chemical state of supported Co-Mo catalysts is studied by XPS. After sulfidation with in-situ method, the majority of molybdenum in CNT supported CoMo catalyst is transferred to a species with a formal chemical state Mo(Ⅳ) in MoS2 phase, and the rest to Mo(Ⅴ) which consists of Mo coordinated both to O and S, such as MoO2S2^2- and MoO3S^2-. In case of CoMo/γ-Al2O3 catalyst sulfided with in-situ method, a fraction of molybdenum is transferred to formal state Mo(Ⅳ) in the form of MoS2, but there is still a mount of unreduced Mo(VI) phase which is difficult to be sulfided. In CoMo/CNT catalyric system sulfided with ex-situ method, Mo(IV) in the form of MoS2 is detected along with a portion of unreduced Mo(VI) phase, suggesting that not all the Mo phases are reduced and sulfided by ex-situ method. As for CoMo/γ-Al2O3, a portion of molybdenum is sulfided to intermediate reduced state Mo(V) which consists of Mo coordinated both to O and S, such as MoO2S2^2- and MoO3S^2-, in addition, there is still a fraction of unreduced Mo(Ⅵ)phase. XPS analyses results suggest that CNT support facilitates the reduction and sulfidation of active species to a large extent, and that alumina support strongly interacts with active species, hereby producing a fraction of phase which resists complete sulfiding. Catalytic measurements of catalysts in the HDS of dibenzothiophene (DBT) show that CoMo/CNT catalysts are of higher HDS activity and selectivity than CoMo/γ-Al2O3 catalyst, which is in good relation with the sulfiding behavior of the corresponding catalyst.     

Investigations of the Growth of Self-Assembled Octadecylsiloxane Monolayers with Atomic Force Microscopy

 Self-assembled monolayers of octadecylsiloxane were prepared and characterized by atomic force microscopy and ellipsometry. Parameters, like the residual water concentration of the solvent and the solution age, that affect both the surface coverage and the order of the film were investigated. Besides ex-situ measurements, also in-situ atomic force microscopy was used to characterize the growth and the kinetics of the adsorption process. Furthermore, self-assembly of organic films was used as a model system for studying the influence of the measurement process on in-situ experiments in the AFM liquid cell.     

合成气制醇钼硫基催化剂上吸附物种的红外光谱表征

利用现场ＦＴＩＲ方法对合成气制混合醇钼硫基催化剂上吸附物种进行了表征。结果表明，在反应条件下，非负载或ＳｉＯ２负载的碱助钼硫基催化剂上主要的ＣＯ加氢中间物种是ＨＣ＝Ｏ、ＣＨ２、ＨＣＯＳ、Ｏ－ＣＨ３及Ｓ＝ＣＨ３，而ＨＣＯＯ＾－和ＣＯ＾２－３的红外指纹谱带却十分弱，难以辨识。推断了该催化体系的反应历程。     

Understanding chemical reactivity for homo‐ and heterobifunctional protein cross‐linking agents

Chemical cross‐linking, combined with mass spectrometry, has been applied to map three‐dimensional protein structures and protein–protein interactions. Proper choice of the cross‐linking agent, including its reactive groups and spacer arm length, is of great importance. However, studies to understand the details of reactivity of the chemical cross‐linkers with proteins are quite sparse. In this study, we investigated chemical cross‐linking from the aspects of the protein structures and the cross‐linking reagents involved, by using two structurally well‐known proteins, glyceraldehyde 3‐phosohate dehydrogenase and ribonuclease S. Chemical cross‐linking reactivity was compared using a series of homo‐ and hetero‐bifunctional cross‐linkers, including bis(sulfosuccinimidyl) suberate, dissuccinimidyl suberate, bis(succinimidyl) penta (ethylene glycol), bis(succinimidyl) nona (ethylene glycol), m‐maleimidobenzoyl‐N‐hydroxysulfosuccinimide ester, 2‐pyridyldithiol‐tetraoxaoctatriacontane‐N‐hydrosuccinimide and succinimidyl‐[(N‐maleimidopropionamido)‐tetracosaethyleneglycol]ester. The protein structure itself, especially the distances between target amino acid residues, was found to be a determining factor for the cross‐linking efficiency. Moreover, the reactive groups of the chemical cross‐linker also play an important role; a higher cross‐linking reaction efficiency was found for maleimides compared to 2‐pyrimidyldithiols. The reaction between maleimides and sulfhydryl groups is more favorable than that between N‐hydroxysuccinimide esters and amine groups, although cysteine residues are less abundant in proteins compared to lysine residues. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on In-Situ Compatibilization of the PP/PA6 Blends in Twin Screw Extruders

The in-situ compatibilization of PP/PA6 blend was studied in a twin screw extruder. The maleic anhydride (MA) content, peroxide concentration, shear rate and feeding order were among the variables investigated. Degree of grafting of samples collected prior to feeding of PA6 into the extruder was measured using titration combined with FTIR technique. From the SEM results it was found that the increasing of initial MA concentration led to larger PA particle size which could be related to secondary reactions between excess MA and PA. The melt linear viscoelastic measurements performed on the blend samples and the obtained relaxation time spectra showed shorter form relaxation time and interfacial relaxation time for one-step compatibilized sample compared to the sample prepared by the two-step method with the same degree of grafting. This was attributed to the stronger interfacial interaction of the one-step compatibilized blend samples which could be resulted from greater efficiency of grafting and/or compatibilization. These results were supported by SEM results which showed smaller particle size for the one-step compatibilized samples. It was demonstrated that melt linear viscoelastic measurement could provide a great insight into understanding the compatibilization process in twin screw extruder.     

可控交联聚醚醚酮的合成与热性能研究

聚醚醚酮因其优异的综合性能 (耐热性、耐水解、耐辐射等 )在许多领域得到应用 [1～ 4 ] .但聚醚醚酮的玻璃化转变温度 ( Tg)较低 ( 4 2 6K) ,导致其使用温度较低 (在 5 1 3K以下 ) .为进一步提高聚芳醚酮类材料的使用温度 ,人们在聚醚醚酮主链中引入刚性结构 ,通过提高聚芳醚酮的刚性度来提高聚芳醚酮的熔点 ( Tm)及 Tg,从而提高材料的使用温度 [5,6 ] .文献 [7]中聚芳醚酮的 Tm 已经高达 741 K,但此材料很难加工成型 .通常热塑性材料具有优异的加工性能 ,但使用温度较低 .热固性材料的使用温度较高 ,但在加工固定尺寸形状铸件时存在困…     

Baked hydrogel from corn starch and chitosan blends cross‐linked by citric acid: Preparation and properties

Citric acid (CA)–modified hydrogels from corn starch and chitosan were synthesized using a semidry condition. This strategy has great benefits of friendly environment because of the absence of organic solvents and compatible with the industrial process. The hydrogel blends were prepared with starch/chitosan ratios of 75/25, 50/50, and 25/75. The thermal stability, morphology, water absorption, weight loss in water, and methylene blue absorption were determined. Multi‐carboxyl structure of CA could result in a chemical cross‐linking reaction between starch, chitosan, and CA. The cross‐linking reaction between free hydroxyl groups of starch, amino groups of chitosan, and carboxyl groups of CA has been confirmed by attenuated total reflectance infrared (ATR‐IR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) analysis. The water absorption properties of CA‐modified hydrogel blends were increased significantly compared with the native starch and chitosan. Moreover, the hydrogel blends modified with CA showed good water resistance and gel content. The morphology study confirmed the complete chemical cross‐linking and porous structure of hydrogel blends. The hydrogel blend with the starch/chitosan ratio of 50/50 presented powerful absorption of methylene blue as well as chemical cross‐linking reaction and dense structure. In sum, the hydrogel blend comprising 50% starch and 50% chitosan has the potential to be applied for water maintaining at large areas, for example, in agriculture.     

Photoswitchable Hydrogel Surface Topographies by Polymerisation‐Induced Diffusion

Herein, we describe the preparation of patterned photoresponsive hydrogels by using a facile method. This polymer‐network hydrogel coating consists of N‐isopropylacrylamide (NIPAAM), cross‐linking agent tripropylene glycol diacrylate (TPGDA), and a new photochromic spiropyran monoacrylate. In a pre‐study, a linear NIPAAM copolymer (without TPGDA) that contained the spiropyran dye was synthesised, which showed relatively fast photoswitching behaviour. Subsequently, the photopolymerisation of a similar monomer mixture that included TPGDA afforded freestanding hydrogel polymer networks. The light‐induced isomerisation of protonated merocyanine into neutral spiropyran under slightly acidic conditions resulted in macroscopic changes in the hydrophilicity of the entire polymer film, that is, shrinkage of the hydrogel. The degree of shrinkage could be controlled by changing the chemical composition of the acrylate mixture. After these pre‐studies, a hydrogel film with spatially modulated cross‐link density was fabricated through polymerisation‐induced diffusion, by using a patterned photomask. The resulting smooth patterned hydrogel coating swelled in slightly acidic media and the swelling was higher in the regions with lower cross‐linking densities, thus yielding a corrugated surface. Upon exposure to visible light, the surface topography flattened again, thus showing that a hydrogel coating could be created, the topography of which could be controlled by light irradiation.