Biodegradable Materials from Agro-Based By-Products

Summary: A new biodegradable thermoplastic material based on a wheat flour by-product has been developed. The influence of various additives (glycerol, silica) and fibers (flax, cotton, hemp) on the mechanical properties of the material has been investigated. The development of expanded materials is also presented.     

Mechanical Properties of Gel-Derived Materials

The mechanical behaviour of xerogels and aerogels is generally described in terms of brittle and elastic materials, like glasses or ceramics. The main difference compared to silica glass is the order of magnitude of the elastic and rupture moduli which are 10⁴ times lower. However, if this analogy is pertinent when gels are under a tension stress (bending test) they exhibit a more complicated response when the structure is submitted to a compressive stress. The network is linearly elastic under small strains, then exhibits yield followed by densification and plastic hardening. As a consequence of the plastic shrinkage it is possible to densify and stiffen the gel at room temperature. These opposite behaviours (elastic and plastic) are surprisingly related to the same two kinds of gel features: the silanol content and the pore volume. Both elastic modulus and plastic shrinkage depend strongly on the volume fraction of pores and on the condensation reaction between silanols. On the mechanical point of view (rupture modulus and toughness), it is shown that pores and silanols play also an important role. Pores can be considered as flaws in the terms of fracture mechanics and the flaw size, calculated from rupture strength and toughness is related to the pore size distribution. Different kinds of gels structure (fractal or not fractal) have been synthesized by a control of the different steps of transformation such as sintering and plastic compaction. The relationships between structural and the elastic properties are discussed in terms of the percolation theory and fractal structure.     

Options to Improve the Mechanical Properties of Protein-Based Materials

While bio-based but chemically synthesized polymers such as polylactic acid require industrial conditions for biodegradation, protein-based materials are home compostable and show high potential for disposable products that are not collected. However, so far, such materials lack in their mechanical properties to reach the requirements for, e.g., packaging applications. Relevant measures for such a modification of protein-based materials are plasticization and cross-linking; the former increasing the elasticity and the latter the tensile strength of the polymer matrix. The assessment shows that compared to other polymers, the major bottleneck of proteins is their complex structure, which can, if developed accordingly, be used to design materials with desired functional properties. Chemicals can act as cross-linkers but require controlled reaction conditions. Physical methods such as heat curing and radiation show higher effectiveness but are not easy to control and can even damage the polymer backbone. Concerning plasticization, effectiveness and compatibility follow opposite trends due to weak interactions between the plasticizer and the protein. Internal plasticization by covalent bonding surpasses these limitations but requires further research specific for each protein. In addition, synergistic approaches, where different plasticization/cross-linking methods are combined, have shown high potential and emphasize the complexity in the design of the polymer matrix.     

Mechanical Properties of 3-Glycidoxypropyltrimethoxysilane Based Hybrid Organic-Inorganic Materials

Hybrid organic-inorganic materials were synthesized from acid catalysed sols of tetraethyl orthosilicate, 3-glycidoxypropyltrimethoxysilane and titanium or zirconium alkoxides. The mechanical properties of these materials were measured in different conditions of preparation. The elastic modulus E was determined by a resonance method and by Knoop microindentation. After a thermal treatment at 125°C for 120 h, E was around 3–5 and 1–2 GPa for the samples synthesized with titanium butoxide or zirconium butoxide, respectively. An increase in E in the samples cured for longer times was observed. Knoop microhardness also increased with the heating time and was larger in samples synthesized from titanium alkoxides than zirconium alkoxides. The two methods gave results in good agreement when applied to samples treated for shorter times. In the other samples Knoop microindentation gave a larger value of E compared to the resonance vibration method. Hardness to elastic modulus ratio, H/E, was evaluated by Knoop microindentation. The elastic recovery at the longest heat treatment time was similar to that of soda-lime glasses. Fracture toughness was measured by three points flexural test, a _KIc in the range of 0.4–0.5 MPa m^1/2 was evaluated for samples treated during 168 h.     

Tuning Mechanical Properties of Block Copolymer/Aluminosilicate Hybrid Materials

In this work the primary mechanical property profiles of a specific class of nano‐structured polymer/inorganic hybrid materials are characterized. By utilizing sol‐gel aluminosilicate synthesis with amphiphilic polyisoprene‐block‐poly(ethylene oxide) block copolymers as structure‐directing agents, block copolymer/aluminosilicate hybrid materials are prepared with nanometer scale hexagonally packed cylinders and lamellae of the inorganic hybrid components, as evidenced by small‐angle X‐ray scattering. Systematic thermal and dynamic mechanical analyses are performed on these hybrids as well as on the constituting components. Results reveal two transitions from the low temperature, glassy state of the hybrids into high temperature elastic plateau regions, with moduli that vary over orders of magnitude as a function of composition and morphology. The first transition can be assigned to the glass transition of the PI domains while the second is ascribed to a temperature induced softening of the organic components within the PEO/hybrid domains. The results suggest that in the present nanostructured block copolymer/aluminosilicate hybrid materials composition and morphology provide a powerful tool to tailor mechanical property profiles.

     

偶联剂对TATB造型粉表面性质及力学性能的影响

采用偶联技术制备TATB造型粉，研究了偶联剂加入前后TATB造型粉的表面行为及其力学性能。结果表明采用偶联技术能够改善TATB造型粉的力学性能和氟橡胶对TATB的粘附。其中，KH550是一种较为理想的改善TATB造型粉性能的偶联剂。     

Mechanical Properties of SiO2-PMMA Based Hybrid Organic-Inorganic Thin Films

Nano-indentations using a Berkovich indenter were performed in order to analyze the mechanical properties of hybrid organic-inorganic coatings. This technique allows to measure low load deformations and therefore to estimate quantitatively mechanical properties of the coatings. The elastic modulus and the hardness were determined on the basis of the load-displacement curve. We report results obtained for class II hybrid coatings based on SiO₂-PMMA prepared by sol-gel process. The effects of coating composition were investigated.     

热塑性淀粉力学性能的提升途径及作用机理

以可再生资源(如淀粉、纤维素和蛋白质等)为基础发展而来的生物可降解塑料受到人们越来越多的关注,是可降解塑料行业发展的重要方向之一。天然淀粉由于来源广、低成本和可生物降解的特点,广泛用于制备淀粉塑料,并用于农业、食品、医药和包装等行业,有望取代石油基衍生聚合物。淀粉大分子具有结晶结构,所含大量羟基可形成较强的分子间和分子内氢键,使其不能热塑加工,而当加入增塑剂后可破坏其结晶结构,从而用于制备热塑性淀粉。目前,热塑性淀粉的力学性能差,是影响其使用性能的首要问题。近年来国内外开展了大量的研究以试图增强其力学性能。本文主要以不同类型的热塑性淀粉为基础,以淀粉自身改性和外加组分改性两种提高其力学性能的途径为主线,以其力学性能的提升方法和作用机理为重点,系统总结了近年来国内外以提高热塑性淀粉材料的力学性能为目的的研究工作,归纳了影响力学性能的相关因素以及提升途径,并对该领域重点研究的内容进行了总结和展望。     

Effect of Aging on Mechanical Properties of Resorcinol-Formaldehyde Gels

Resorcinol-Formaldehyde gels have been prepared in aqueous solutions. After a gelification stage at 80°C, an aging was performed in water or acetic acid solutions at ambient temperature or in the parent liquid at 80°C for different durations. Shear modulus of gels immersed in water is measured using the 3 points bending technique. The evolution of elastic constant with time depends on the pH of aging solution. The strengthening is more pronounced for aging under acidic conditions than in water. Nevertheless when the aging stage is performed at 80°C for a few days, quite identical values of shear modulus are obtained comparatively to acid treatment. The enhancement of mechanical properties of RF gels in acidic conditions is related to polycondensation reaction rates.     

Effect of Bee Pollen on the Mechanical and Thermal Properties of Starch Films

The use of casein, starch and bee pollen as biodegradable materials has been promise. The objective of this work was the development and characterization of films containing casein, pollen and starch. The films were obtained by casting process and the solvent evaporation was performed at 40 °C/24 h. The films characterization was carried out by microscopy, thermal analysis, opacity test, mechanical properties and barrier methods. The starch films presented heterogeneous on microscopy analysis. The thermal behaviors of pollen films were similar. The formulation containing only pollen 3% was unable to form film. The introduction of pollen in starch film formulation improved the mechanical characteristic and thermal stability of films.     

镧、钇对90W-Ni-Fe合金显微结构及性能的影响

以喷雾干燥 H2还原法制备的纳米级90W 7Ni 3Fe复合粉末为原料,针对不同稀土元素La,La Y,Y含量对90W Ni Fe合金性能和显微结构的影响进行了研究。结果表明:当添加La,La Y,Y在0～0.8%(质量分数)范围时,试样相对密度均在0.4%稀土时出现极大值,分别为99.3%,99.4%,99.6%。添加0.4%的La或La Y时,试样抗拉强度出现极大值,分别是906和983.5MPa,而当添加0.6%Y时,试样抗拉强度出现极大值1078MPa。添加0.2%La和Y时,试样延伸率出现极大值分别为17%和19.5%。添加La对W晶粒的抑制作用不明显,添加0.4%Y后对W晶粒长大的抑制作用较为明显,W晶粒尺寸从原来的15～20μm减少到10～15μm,W晶粒由不加稀土时的球形变为近球形或多边形,且随稀土含量的增加其影响作用更明显。La,La Y,Y同W,Ni,Fe3种元素在晶界上分别形成了W12.95Ni3.42Fe1.93La27.51,W13.61Ni2.61Fe1.07Y20.52La25.27,W13.07Ni2.96Fe1.52Y23.65(摩尔比)的中间相。添加稀土元素后,使得W在粘结相中的溶解度明显下降,由58.65%下降为添加0.4%La Y时的29.86%。当添加相同含量的稀土元素时,对合金性能影响程度的大小顺序是Y>La Y(混合稀土)>La。     

稀土对AM50力学性能及高温蠕变的影响

对Y和富La稀土对镁合金AM50微观组织、铸态力学性能和蠕变性能的影响进行了研究.研究结果表明: AM50中加入Y和富La稀土能有效地细化晶粒,由于显微组织的改善,使得AM50合金的室温和高温力学性能均有一定的提高,并明显地改善了AM50镁合金的抗蠕变性能.填加稀土可以在AM50合金晶界处生成稳定的铝稀土化合物,可以明显提高镁合金AM50的常温及高温(150 ℃)力学性能.与加入富La稀土的AM50相比,加入Y提高力学性能及蠕变抗力的作用更明显.     

The Influence of the Addition of Nuts on the Thermal and Rheological Properties of Wheat Flour

The aim of the study was to assess the influence of replacing wheat flour with hazelnuts or walnuts, in various amounts, on the thermal and rheological properties of the obtained systems. The research material were systems in which wheat flour was replaced with ground hazelnuts (H) or walnuts (W) in the amount of 5%, 10%, and 15%. The parameters of the thermodynamic gelatinization characteristics were determined by the differential scanning calorimetry method. In addition, the pasting characteristics were determined with the use of a viscosity analyzer and the viscoelastic properties were assessed. Sweep frequency and creep and recovery tests were used to assess the viscoelastic properties of the tested gels. It was found that replacing wheat flour with nuts increased the values of gelatinization temperature, gelatinization, and retrogradation enthalpy, and the degree of retrogradation. The highest viscosity was characteristic of the control sample (2039 mPa·s), and the lowest for the paste with 15% addition of walnuts (1120 mPa·s). Replacing the flour with nuts resulted in a very visible reduction in the viscosity of such systems. In addition, gels based on the systems with the addition of H and W were weak gels (tan δ = G″/G′ > 0.1), and the values of G′ and G″ parameters decreased with the increased share of nuts in the systems. Creep and recovery analysis indicated that the systems in which wheat flour was replaced with hazelnuts were less susceptible to deformation compared to the systems with the addition of W.     

Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds shows smooth rheological behavior and mechanical properties. Variation in rheological behavior and mechanical properties was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica CB/Si = 0/60, 20/40, 30/30, 40/20 and 60/0 phr (parts per hundred rubber is parts of any non-rubbery material per hundred parts of raw gum elastomer (rubbery material)). The rheological behaviour can be showed in measurement of Mooney viscosity and cure time. The Mooney viscosity of rubber compounds increase with the increasing the carbon black in the compounds. The compound filled with CB/Si of 30/30 and 60/0 showed abnormal rheological behaviour in which the cure time decreased suddenly and the increased at certain ratio during the measurement. The mechanical properties such as hardness, abrasion resistance and tensile stress at 300% elongation were studied. In the hardness and abrasion resistance measurement, the higher ratio CB/Si decrease contribution of silica, which resulting smaller of hardness value. Ratio CB/Si 40/20 gives an optimum filler blended. It is also clearly understood that higher abrasion resistance mainly due to the lower hardness value under the same condition. The tensile stress at 300% elongation of rubber compound increased with the increasing carbon black filler.     

碳纳米管含量对炭炭复合材料组织及力学性能的影响

炭纤维上原位合成了均匀生长且具有伸张形貌的碳纳米管,借助化学气相渗透制备了碳纳米管增强的炭炭复合材料,研究了不同含量的碳纳米管对炭炭复合材料组织和力学性能的影响。结果表明：炭纤维上生长碳纳米管改变了热解炭的沉积行为,诱导了各向同性热解炭的生成,且随着碳纳米管含量的增加,各向同性热解炭的厚度增加,但是复合材料的d002值却明显降低。微量的碳纳米管即可显著提高复合材料的力学强度,随着其含量的增加,复合材料的力学强度和模量迅速提高,但材料的断裂行为却急剧恶化,断裂模式由最初的假塑性断裂转变为脆性断裂。     

Influence of the Epoxy/Acid Stoichiometry on the Cure Behavior and Mechanical Properties of Epoxy Vitrimers

Bisphenol A epoxy resin cured with a mixture of dimerized and trimerized fatty acids is the first epoxy vitrimer and has been extensively studied. However, the cure behavior and thermal and mechanical properties of this epoxy vitrimer depend on the epoxy/acid stoichiometry. To address these issues, epoxy vitrimers with three epoxy/acid stoichiometries (9:11, 1:1 and 11:9) were prepared and recycled four times. Differential scanning calorimetry (DSC) was used to study the cure behavior of the original epoxy vitrimers. The dynamic mechanical properties and mechanical performance of the original and recycled epoxy vitrimers were investigated by using dynamic mechanical analysis (DMA) and a universal testing machine. Furthermore, the reaction mechanism of epoxy vitrimer with different epoxy/acid stoichiometry was interpreted. With an increase in the epoxy/acid ratio, the reaction rate, swelling ratio, glass transition temperature and mechanical properties of the original epoxy vitrimers decreased, whereas the gel content increased. The recycling decreased the swelling ratio and elongation at break of the original epoxy vitrimers. Moreover, the elongation at break of the recycled epoxy vitrimers decreased with the epoxy/acid ratio at the same recycling time. However, the gel content, tensile strength and toughness of the original epoxy vitrimers increased after the recycling. The mechanical properties of epoxy vitrimers can be tuned with the variation in the epoxy/acid stoichiometry.