Yi Dan

Study on the Effect of Dicumyl Peroxide on Structure and Properties of Poly(Lactic Acid)/Natural Rubber Blend

In attempt to enhance the compatibility of NR in PLA matrix, and furthermore to enhance mechanical properties of PLA, PLA/NR blends with strong interaction were prepared in Haake internal mixer, using dicumyl peroxide (DCP) as cross-linker. The effects of dicumyl peroxide on morphology, thermal properties, mechanical properties and rheological properties of PLA and PLA/NR blends were studied. The results indicated that dicumyl peroxide could increase the compatibility of poly(lactic acid) and natural rubber. With small amount of dicumyl peroxide, the effect on NR toughening PLA was enhanced and the tensile toughness of PLA/NR blends was improved. When the DCP content was up to 0.2xa0wt%, the PLA/NR blend reached the maximum elongation at break (26.21xa0%) which was 2.5 times of that of neat PLA (the elongation at break of neat PLA was 10.7xa0%). Meanwhile, with introducing 2xa0wt% DCP into PLA/NR blend, the maximum Charpy impact strength (7.36xa0kJ/m2) could be achieved which was 1.8 times of that of neat PLA (4.18xa0kJ/m2). Moreover, adding adequate amount of DCP could improve the processing properties of blends: the viscosity of PLA/NR blend decreased significantly and the lowest viscosity of the blends could be achieved when the DCP content was 0.5xa0wt%.

Microdynamics mechanism of thermal-induced hydrogel network destruction of poly(vinyl alcohol) in D2O studied by two-dimensional infrared correlation spectroscopy.

Microdynamics mechanism of thermal-induced hydrogel network destruction of poly(vinyl alcohol) (PVA) in D2O at heating (25-62 °C) was studied by in situ Fourier transform infrared (FTIR) spectroscopy combining with moving-window two-dimensional (MW2D) technique and two-dimensional (2D) correlation analysis. The temperature range of hydrogel destruction was determined within 34-52 °C by dynamic rheological test at first, and then also monitored by MW2D FTIR spectra. The motion of vs(-C-O-, microcrystals) was important in the entire hydrogel destruction process. The microdynamics mechanism of PVA molecular chains can be elaborated as follows: At 32 °C, the number of D2O molecules in the swollen amorphous remains unchanged. At 32-37 °C, more D2O molecules enter into the swollen amorphous region, and the groups of -C-O-, together with -CH2-, are partially hydrated. At 37 °C, the intramolecular or intermolecular hydrogen bonds of PVA are dissociated. The physical cross-linking points of hydrogel are broken due to the melting of PVA microcrystals. At 42 °C, the dissociated hydroxyls from PVA microcrystals rapidly integrate solid hydrogen bonds with D2O molecules. The groups of -C-O- and -CH- are completely hydrated by D2O simultaneously. At 45-55 °C, PVA molecules are surrounded by more D2O molecules. The partially hydrated -CH2- is completely hydrated, and all of the PVA molecules are fully dissolved in D2O.

Enhanced ductility of polylactide materials: Reactive blending with pre-hot sheared natural rubber

Both polylactide (PLA) and natural rubber (NR) are biocompatible and biodegradable. PLA performs high strength and modulus but low toughness, while NR exhibits excellent elasticity and ductility. In view of their complementary properties, NR seems an ideal candidate to toughen PLA. To the best of our knowledge, PLA and rubber blends usually show notable enhancement in ductility when more than 10xa0% rubber was added, but accompanied by great loss in mechanical strength. This study demonstrates a significant improvement in the toughness of PLA by its melt blending with pre-hot sheared natural rubber (NR). With as little as 3xa0% pre-hot sheared NR for 10xa0min, the elongation at break and tensile toughness were significantly improved over that of pure PLA (196.2xa0% vs. 16.3xa0% and 77.5xa0MJ/m3 vs. 8.8xa0MJ/m3, respectively) with a slight loss in tensile stress. FTIR spectra indicated that carbonyl groups generated in NR chains after hot shearing and led to the enhanced interfacial adhesion between PLA and NR. The SEM studies showed that the rubber phase was uniformly dispersed in PLA matrix in NR/PLA blends with 3xa0% rubber content. The addition of NR after hot shearing for 10xa0min reduced the glass transition temperature of PLA, which was characterized by DSC measurement. Rheological measurements also proved a better compatibility of the blend with pre-hot shearing of NR for a longer time.

Time‐Dependent Aggregation‐Induced Enhanced Emission, Absorption Spectral Broadening, and Aggregation Morphology of a Novel Perylene Derivative with a Large D–π–A Structure

Strong aggregation-caused quenching of perylene diimides (PDI) is changed successfully by simple chemical modification with two quinoline moieties through C=C at the bay positions to obtain aggregation-induced enhanced emission (AIEE) of a perylene derivative (Cya-PDI) with a large π-conjugation system. Cya-PDI is weakly luminescent in the well-dispersed CH(3)CN or THF solutions and exhibits an evident time-dependent AIEE and absorption spectra broadening in the aggregated state. In addition, morphological inspection demonstrates that the morphology of the aggregated form of Cya-PDI molecules changed from plate-shaped to rod-like aggregates under the co-effects of time and water. An edge-to-face arrangement of aggregation was proposed and discussed. The fact that the Cya-PDI aggregates show a broad absorption covering the whole visible-light range and strong intermolecular interaction through π-π stacking in the solid state makes them promising materials for optoelectric applications.

Effect of surface tension on the properties of a doped CeO2–ZrO2 composite and its application in a Pd-only three-way catalyst

La and Pr modified ceria–zirconia solid solution materials CeO2–ZrO2–La2O3–Pr6O11 (CZLP) were synthesized through a co-precipitation method, in which the influence of surface tension during the drying process on the textural/structural properties, reduction behavior and oxygen storage capacity of the materials was investigated. The difference in catalytic performance of the supported Pd-only thee-way catalysts was further studied. The results revealed that CZLP3 obtained through a supercritical ethanol drying method which eliminated the surface tension in the drying process exhibited a texture with a larger pore size and wider pore size distribution. Such texture is crucial to improve the thermal stability and anti-aging ability of materials. After calcining at 1000 °C, the specific surface area, cumulative pore volume and average pore radius of CZLP3-a were 52 m2 g−1, 0.52 cm3 g−1 and 20.3 nm, respectively. The XRD and Raman results revealed that a more homogeneous solid solution of Ce, Zr, La and Pr was formed, and the aging-treatment-induced segregation of phases was inhibited for CZLP3. Besides, the slightest grain growth after the aging treatment shown in TEM images indicated the superior anti-aging ability of CZLP3. The Raman and XPS analysis demonstrated the highest concentration of oxygen vacancies and surface Ce3+ species for CZLP3 both before and after the aging treatment, which contributed to the enhancement of its reduction properties and oxygen storage capacity. Consequently, Pd/CZLP3 exhibited outstanding three-way catalytic activity compared with the others both before and after the thermal aging treatment, indicating its tremendous potential possibilities.

Effect of the content and distribution of ultraviolet absorbing groups on the UV protection and degradation of polylactide films

Introduction of a UV absorbing group onto a polymer chain through covalent bonding greatly reduced the UV light transmittance of the resulting polylactide (PLA) film and preserved the high transparency to visible light. Compared to simply blending a UV absorber with a PLA matrix, covalent bonding of the UV absorbing group with polylactide enabled the prepared films to have better dispersion of the UV absorbing group, stable solvent resistance, better protection effect against UV damage and a slower rate of UV irradiated degradation, while the distribution of the UV absorbing group made no difference to the aforementioned properties. The degradation of both the PLA film covalently bonded with a UV absorbing group and the PLA/UV-absorber blended film followed the same mechanism as pure PLA films, in that the alkyl-oxygen bond broke first to produce acyl-oxygen and secondary carbon radicals, which then captured hydrogen to form carboxyl groups and alkyl groups at the end of the fractured polymer chain. More UV absorbing groups at the chain end were favorable for reducing UV transmittance, providing a better protection effect on the packaged probe, and slowing the UV irradiated degradation of PLA film. The thermal stability was dependent on the molecular weight of polylactide and was hardly affected by the introduction of the UV absorber or UV absorbing group.

Systematic investigation of the synthesis and light-absorption broadening of a novel diketopyrrolopyrrole conjugated polymer of low and high molecular weight with thermo-labile groups

To strengthen the π–π stacking interaction of conjugated polymer chains and study the absorption broadening effect, a narrow band-gap copolymer with high (DPP-Car-Boc-H) and low (DPP-Car-Boc-L) molecular weight, comprising alkyl substituted diketopyrrolopyrrole (DPP) and t-butoxycarbonyl (t-Boc)-protected carbazole (Car-Boc) units, is designed and synthesized. The absorption broadening is investigated on the basis of molecular weight, solution and solid state, solution temperature and nonsolvent effect. FTIR analysis confirmed the decomposition of t-butoxycarbonyl protecting groups after thermal annealing treatment. It is found that the removal of thermo-labile groups (t-Boc) at 180 °C and the liberation of active NH groups further broaden the light-absorption spectra in thin films due to the intensified π–π stacking interaction between polymer chains which is verified through TGA, SEM and XRD. After thermal annealing, SEM images exhibited cubic crystals spread uniformly and the increased order degree of aggregation was verified further. Additionally, the impact of electronic structure change on the photo-response broadening effect is excluded by Gaussian molecular simulation. This work provides a viable approach and convincing evidence that thermal fabrication strengthens conjugated polymer chain stacking through the large π-delocalized plane and provides broad absorption properties for use in photoelectric devices.

Macromolecular chain structure design, synthesis and analysis of poly(L-lactide) linking ultraviolet absorbing groups

Poly(L-lactide) (PLA) with different chain structures was designed, and successfully synthesized by ring opening polymerization using 2-hydroxy-4-(3-methacryloxy-2-hydroxylpropoxy) benzophenone (BPMA), 2,2′-dihydroxy-4,4′-(2-hydroxylpropoxy) dibenzophenone (DHDBP) and 2-hydroxy-4-(2,3-dihydroxylpropoxy) benzophenone (HPBP) as initiators, respectively, to produce corresponding PLA-B (end-capped with BPMA), PLA-DB (end-capped with DHDBP) and PLA-HB-PLA (blocked with HPBP in the middle). High-molecular-weight PLA-DB400 with good visible light transparency and UV opacity was prepared. The chemical structures of the samples were characterized, the crystallization behavior, thermal stability, UV absorption properties and transmittance of PLA were investigated and analyzed. Results of GPC and DSC reveal that when the number average molecular weights (Mn) of PLA are around 4000, termination of a UV absorbing group like DHDBP greatly restricts the crystallization of PLA due to the larger volume and rigidity of the end-capping group, but increasing Mn to about 12000 or higher weakens the hindering effect, resulting in a similar degree of crystallization (Xc). TG results show that PLA-DB400 has the best thermal stability due to the highest molar mass. When the UV absorber is blocked in the PLA chain, the restriction and steric hindrance of the absorber are much stronger than that in the end-capped material, making Xc significantly reduced. UV absorbance of the PLA solutions reveals that the introduction of UV absorbing groups gives an absorption to UV light below 350 nm and the position of the introduced groups has no influence on the UV absorption properties although the content of the UV group does enhance the UV absorbance, of which PLA-DB has the highest since DHDBP bears two 2-dihydroxybenzophenone groups. The transparency of PLA films is neither affected by position nor content of the introduced UV absorbing groups, which is very beneficial for the application of PLA in packaging materials that require high transparency.

Acrylamide modified poly(vinyl alcohol): crystalline and enhanced water solubility

Acrylamide (AAm) modified polyvinyl alcohol (PVA) with enhanced water solubility and tunable tacticity and crystallinity was prepared by alcoholysis of vinyl acetate (VAc) and acrylamide copolymers. The chemical structures and performance of VAc–AAm copolymers and AAm-modified PVA were measured by FTIR, UV-vis, XRD, elemental analysis as well as rheometry. FTIR and XRD analysis reveals that AAm units in PVA chain can reduce the stereoregularity effectively, and suppress the crystallinity. And a decreasing linear relationship between crystallinity and AAm mole fractions is observed. Furthermore, the influence of AAm modification on the water solubility of PVA was studied, and a significant enhancement either at low temperature (30 °C) or at high temperature (70 °C) was achieved through AAm modification. Moreover, the rheological investigation suggested that the relative strength of the hydrogen bonding interactions existing between PVA chains was weakened, while those between PVA chains and water molecules, to some extent, were enhanced after AAm modification. The method presented is an easy but promising way to prepare PVA that can have good water solubility even at low temperature while exhibiting high degrees of alcoholysis.

FTIR analysis on aging characteristics of ABS/PC blend under UV-irradiation in air

Fourier Transform Infrared Spectroscopy (FTIR) is adopted to study the aging characteristics of poly(acrylonitrile-butadiene-styrene)/polycarbonate (ABS/PC) blend under UV-irradiation in air by analyzing the variation of the three main absorbance at about 967cm-1, 1720cm-1 and 3420cm-1 associated with carbon-hydrogen bonds belonging to 1,4 butadiene, carbonyl and hydroxyl groups, respectively. Results indicate that, under UV-irradiation in air, the photo-oxidation of the blend is not a simple combination of the photo-oxidation of corresponding ABS and PC themselves and takes place predominantly at the ABS component. Due to the interaction between the two components and the Fries rearrangement taken place in the PC component during the UV-irradiation in air, the ABS/PC blends behave higher photo-stability than ABS has.