•Following structure change by FTIR, the aging characteristics of ABS/PC blend under UV-irradiation in air were studied.•The photo-oxidation-aging of the ABS/PC blend takes place predominantly at the ABS component.•The ABS/PC blend behaves higher photo-oxidation-stability than ABS has.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 967 cm− 1, 1720 cm− 1 and 3420 cm− 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.Download high-res image (313KB)Download full-size image

•The hydrolytic rates of PLA and the blends were related to the initial morphology.•Crystalline affected the effect of the fluoropolymers on the PLA’ hydrolysis.•The miscibility and dispersion influenced the hydrolytic rate of PLA.Hydrolytic behaviors of poly(lactic acid) (PLA) films with different crystallinities (∼0, 30 and 40%) containing hydrophobic fluoropolymers were studied by evaluating the hydrophobicity and water absorption through measuring contact angle and FTIR, and by investigating the evolution of average molecular weights, morphology and thermal property. The results showed that the hydrophobic fluoropolymers enhanced the hydrophobicity of the surface of PLA, where water contact angle increased about 20°, but they did not cause a decrease in water absorption in the bulk of PLA. The hydrolytic rate of samples was affected by both crystallinity of the PLA component and dispersion of the hydrophobic fluoropolymers. For amorphous samples, the fluoropolymers could well disperse in the PLA substrate and accelerate the hydrolysis of PLA component. The amorphous PLA had a hydrolytic rate of 0.0335 week−1, while the rate of the amorphous sample with hydrophobic fluoropolymers increased up to 0.0458 week−1. For the crystallized samples, neat PLA hydrolyzed faster than the blends. For example, the rate of PLA crystallized at 90 °C was 0.0423 week−1 while the values of the blends with PLA-b-PFMA10 and PLA-b-PFMA20 were 0.0325 and 0.0260 week−1, respectively. The difference between the blends was related to the dispersion of the fluoropolymers that the badly-dispersed fluoropolymer had better hydrolytic resistance effect than that of the well-dispersed fluoropolymer.Download high-res image (82KB)Download full-size image

Comparative discussions on photo-physical and aggregating properties of D–π–A perylene diimide derivatives with soft n-octylamine (PDI-soft) and hard quinoidal (PDI-hard) substituents on the bay position were put forward to reveal structure–property relations. UV–vis spectrometer and fluorospectro photometer were used to characterize the absorption and emission properties of derivatives in various solutions. The PDI-hard aggregated in both Hexane and THF/water systems and showed an interesting time-dependent aggregation-induced enhanced emission (AIEE) phenomenon. PDI-soft also aggregated in poor solvents as Hexane or Acetonitrile and exhibited broad light absorption range making PDI-soft a candidate for photoelectric materials. Morphologies of solid aggregations formed from solutions were observed by means of scanning electron microscopy. Results showed that PDI-hard molecules aggregated to sheets structure after the evaporation of Hexane while PDI-soft obtained a wire-like structure through a slipped π-π stacking in the system of THF and water. The comparison of photo-physical properties and morphologies between PDI-hard and PDI-soft suggests that a subtle choice of the bay substituents makes the controllable photo-physical and aggregating properties possible.

In this paper a series of di-block copolymers of L-lactide and (meth)acrylate [(M)A, representing methyl methacrylate, tert-butyl acrylate and 2-ethylhexyl acrylate] were synthesized by varying the molecular weight of the polylactide (PLLA) macroinitiator and the structure of the (meth)acrylate monomers. The glass transition temperature, crystallinity and thermal stability of copolymers with different poly(meth)acrylate [P(M)A] blocks were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results indicated that the glass transition temperature of the copolymers could be tuned by changing the chain structure and chain length of the P(M)A blocks. Besides, the crystallization of the copolymers was inhibited by the introduction of P(M)A blocks, and the toughness of the copolymers could be tuned. It is noted that the thermal stability of the copolymers depended on the type of P(M)A blocks and the PLLA/P(M)A blocks ratio. Furthermore, the microphase separation of copolymers in thin films was observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the results showed that the composition of copolymers significantly affected the surface morphology of the block copolymer thin films.

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.

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.

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.

By the application of artificial neural network (ANN), the concept of constructing polymers' aging life prediction system has been proposed for the first time in the present work. Such a system can be designed via integrating several independent ANN modules playing different roles: the S module for calculating environmental stress level, the F module for outputting the feature of aging life distribution, the Sa module for computing the accelerated environmental stress level, the aT module for studying the correspondence between life distribution of certain accelerated and natural aging tests, and the structure module for converting polymer structures into structure parameter matrix. Here polycarbonate, as a widely used engineering thermoplastic with complex aging behavior and various aging mechanisms, has been researched to constructing its aging life model with the help of the systematic ANN method above, which well reflects huge potential of ANN's application in the field of polymers' aging life prediction for practical application.

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.

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.

Bisphenol A polycarbonate (PC) was chosen as the representation of polyester resins for investigating the effect of aggregative state on hydrolytic stability of this kind of materials. Surface-crystallized PC was prepared by solvent-induced crystallization method. Moreover, a comparative study on hydrolytic stability of amorphous PC and surface-crystallized PC had been carried out by means of mechanical performance testing, static water contact angle, IR, GPC and DSC measurements. The results indicated that the surface-crystallized PC had better hydrolytic stability than amorphous PC, manifesting as: (1) the hydrophobicity of PC was enhanced obviously when the surface of material crystallizes via solvent-induced method; (2) the reduced rate of the elongation at break of surface-crystallized PC was much smaller than that of amorphous PC during hydrolysis; (3) the impact strength of amorphous PC reduced rapidly in the early stage of hydrolysis, while that of surface-crystallized PC firstly increased, following by a slightly decrease; (4) the reduced rate of weight-average molecular weight of surface-crystallized PC was smaller than that of amorphous PC; and (5) the stability of the chemical structures of surface-crystallized PC was much higher than that of amorphous PC during hydrolysis, resulting in fewer changes in the glass transition temperature (Tg), as well as less cleavage of polycarbonate linkage after hydrolysis in 65 °C water for 36 days. This investigation clearly shows that solvent-induced crystallization on surface can be an efficient way to enhance the hydrolytic stability of polycarbonate.

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 0.2 wt%, the PLA/NR blend reached the maximum elongation at break (26.21 %) which was 2.5 times of that of neat PLA (the elongation at break of neat PLA was 10.7 %). Meanwhile, with introducing 2 wt% DCP into PLA/NR blend, the maximum Charpy impact strength (7.36 kJ/m2) could be achieved which was 1.8 times of that of neat PLA (4.18 kJ/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 0.5 wt%.

A novel visible light active photo-catalyst named CHC/C-PVA/TiO2, the composite of titanium dioxide (TiO2) with conjugated derivative of polyvinyl alcohol (C-PVA) loaded on a cordierite honeycomb ceramic (CHC) substrate, was fabricated by combining the synthesis of TiO2 sol, preparation of C-PVA via thermally treating polyvinyl alcohol, and immobilization of TiO2 sol and C-PVA on CHC. By detecting the change of UV–vis absorption spectra of the model organic pollutant (methyl orange (MO)) in the presence of the composite under visible light irradiation, the photo-catalytic activity was evaluated and the results show that the CHC/C-PVA/TiO2composite has an enhanced photo-catalytic activity when compared to the CHC/TiO2 composite. Besides, the CHC/C-PVA/TiO2 shows a good photo-catalytic stability after the fourth cycles. The structure analyses by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) show the coexistence of C-PVA and TiO2 on the CHC and the cracks on the surface of CHC/C-PVA/TiO2. Result of ultraviolet-visible diffuse reflection spectroscopy (UV–vis DRS) reveals that the CHC/C-PVA/TiO2 can absorb both ultraviolet and visible light while result of X-ray photoelectron spectroscopy (XPS) indicates the existence of C, O and Ti elements in the CHC/C-PVA/TiO2. The typical structures as well as the optical characteristics of the CHC/C-PVA/TiO2 are responsible for the enhancement in the photo-catalytic activity.A novel photocatalyst CHC/C-PVA/TiO2 with cordierite as the support and PVA as the precursor of conjugated polymer was prepared and it shows superior photocatalytic activity under visible light.Download high-res image (132KB)Download full-size image

Herein, we report a new approach to fabricate polyvinyl alcohol (PVA) based hydrophilic monoliths by alcoholysis of porous emulsion-templated polyvinyl acetate (PVAc). The precursory PVAc-based monolith is obtained by polymerization of a W/O high internal phase emulsion (HIPE) containing vinyl acetate as the external phase while water as the internal phase. As an alcoholysis-stable tri-functional commonomer, triallyl isocyanurate is chosen as the crosslinking agent to prevent possible collapse of the polymeric skeleton and the consequent losses in mechanical properties during the alcoholysis step. By alcoholysis of the resulting PVAc-based monolith, the PVA-based monoliths are successful prepared as confirmed by FTIR analysis. BET analysis and SEM observation confirm the formation of open-cell and highly interconnected porous structures of PVA-based monoliths with surface areas of around 16 m2/g. Stemming from the intrinsic hydrophilicity of hydroxyl and morphology, PVA-based monoliths exhibit great enhancement in hydrophilicity with a much lower water contact angles than that of PVAc-based monoliths.