CHARACTERIZATION OF γ-IRRADIATED CRYSTALLINE POLYMERS Ⅱ ISOTHERMAL CRYSTALLIZATION KINETICS OF γ-RADIATION INDUCED CROSSLINKED POLYAMIDE 1010

Polyamide 1010 is a γ-radiation crosslinkable polymer. After irradiation, it is possible to raise its service temperature up to 240℃. Network formation greatly changes the crystallization behaviour of the polymer. In the present work, DSC was used to examine its isothermal crystallization kinetics. It is found that in addition to the necessity of more undercooling and the lowering of crystallization rate, the primary crystallization stage of the irradiated polymer is shortened. This effect is more evident with increasing radiation dose and content of enhanced difunctionai erosslinking agent. However, the crystallization mechanism of the primary stage is not changed as evidenced by the constancy of Avrami exponent. The lamella end surface free energy σ_e calculated according to Hoffman's equation is very sensitive to γ-radiation. It increases abruptly in 2—3 fold even though the radiation dose is not high enough. The origin of this phenomenon may be accounted for in terms of network structure of the polymer.     

STRUCTURE EFFECTS ON THE SOL FRACTION-DOSE RELATIONSHIP IN RADIATION CROSSLINKING OF POLYMERS

The structure effects of polymers on the relationship between sol fraction and radiation dose arediscussed in detail. In consideration of the deviation of experimental results from Charlesby-Pin-ner's and Chen-Liu-Tang's expressions relating sol fraction to radiation dose, we introduced an ex-ponent βconcerned with the structure and property parameters of a polymer (glass transition tem-perature T_g and molecular internal rotating steric factor δ) and assumed that the fracture density isproportional to R~β(R is radiation dose). Thus, a general expression, formula (9), relating solfraction to radiation dose is derived. When β=1 andβ=0.5, this expression is reduced to the above-said two expressions. Us-ing this general expression, the experimental data of a number of polymers are treated. It is shownthat the expression is in good agreement with the experimental results, βvalue is in the range of 0. 5 to1.0.     

NAD~ ANALOGS IN FORMATION OF NEW FLUOROPHORES ON ULTRAVIOLET IRRADIATION WITH D-GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE

A number of NAD~ analogs have been tested in their ability to form fluorescent deriva-tives when UV irradiated with the active site Cys-149 carboxymethylated GAPDH and this hasbeen compared with their properties of acting as hydrogen acceptors and forming the Rackerband. Among the analogs tested, NHD~ , NGD~ , APAD~ and ∈NAD~ give positive results inall the above-mentioned reactions whereas αNAD~ , NMN~ and CPAD~ are all negative.FPAD~ forms a fluorescent derivative on UV irradiation with the carboxymethylated enzymebut is inactive as a hydrogon aceeptor and does not form the Racker band. This is probablydue to thiohemiacetal formation of the pyridine 3-aldehyde of this derivative with the activesite SH group required for both the latter 2 reactions. TPAD~ , although active as a hydrogenacceptor, does not form either a fluorescent derivative or a Racker band. The fact that forthe great majority of the analogs, the property of forming fluorescent derivatives is is parallelwith their hydrogen acceptor activity seems to show that the formation of the fluorescentderivative is indeed at the active site, and hence can be used as an intrinsic probe for thestudy of the conformation of the active site of this enzyme.     

常温预辐射聚合法物理包埋葡萄糖氧化酶的研究

Most of bioactive species such as enzyme and antibody will be damaged and lose part of their bioactivity when they are irradiated by ionizing radiation at room temperature. Low temperature could somewhat control the effect, so kaetsu and his co-workers developed an entrapping technique at low temperature ( - 78℃). On the other hand, some enzymes such as catalase and house radish peroxidase have so-called radiation-induced post-deactivation effect as well. In order to avoid the trouble in performance and loss of bioactivity, a physical ent-rapping of bioactive species via preirradiation polymerization at room temperature were deve-loped in the Authors'lab. In this work we developed this technique. The glucose oxidase was entrapped in polyacrylamide hydrogel ind uced by pre-irradiation. Experiments under several different conditions such as absorbed dose and concentrations of enzymes,monomer and crosslinking agent were carried out. The results showed that this technique can be used ex-tensively in various enzyme.     

Preheat Compression Molding for Polyetherketoneketone: Effect of Molecular Mobility

Polyetherketoneketone(PEKK)is a new evolving polymeric material,and is considered as another important member of the polyaryletherketone(PAEK)family in addition to polyetheretherketone(PEEK).Hot compression molding can be used to compact and consolidate the PEKK products,where the temperature and pressure play key roles to affect the molecular mobility,entanglement and crystallization,and thus the mechanical properties of PEKKs.In this study,a preheating treatment was introduced in the compression molding,and it is found that such preheating is very essential to avoid the formation of crystal FormⅡ,based on the increased chain entanglement.Molecular dynamics simulations revealed that the molecular mobility is always suppressed when a compression is applied.Therefore,by increasing the entanglement via the preheating and maintaining such entanglement in the consequent compression molding,strong and tough PEKK materials were obtained,with a negligible fraction of crystal FormⅡ.     

Nitrogen-doped graphene as an excellent candidate for selective gas sensing

The toxic gases,such as CO and NO,are highly dangerous to human health and even cause the death of person and animals in a tiny amount.Therefore,it is very necessary to develop the toxic gas sensors that can instantly monitor these gases.In this work,we have used the first-principles calculations to investigate adsorption of gases on defective graphene nanosheets to seek a suitable material for CO sensing.Result indicates that the vancancy graphene can not selectivly sense CO from air,because O2 in air would disturb the sensing signals of graphene for CO,while the nitrogen-doped graphene is an excellent candidate for selectivly sensing CO from air,because only CO can be chemisorbed on the pyridinic-like N-doped graphene accompanying with a large charge transfer,which can serve as a useful electronic signal for CO sensing.Even in the environment with NO,the N-doped graphene can also detect CO selectively.Therefore,the N-doped graphene is an excellent material for selectively sensing CO,which provides useful information for the design and fabrication of the CO sensors.     

THE EFFECTS OF IRRADIATION ON THE THERMAL PROPERTIES OF SEMI-CRYSTALLINE POLYAMIDES

Irradiation crosslinking of semi-crystalline polyamides was performed by high energy electronswith various dosages. It is known that the melting behavior of the polymers after irradiation is acomplex phenomenon. In company with the wide angle X-ray diffraction and DSC data of irradiatedand unirradiated polyamides it is possible to develop the local order and perfection of the crystallinitiesslightly which resulted from introduction of intermolecular crosslinking in amorphous region, incl-uding in amorphous-crystalline interface and crystalline defect regions due to irradiation. It canbe explained that slight increase of melting temperature (T_m) and heat of fusion (△H_f) with increasingdosage for both of higher crystallinity nylon 4 and nylon 6. For irradiated lower crystallinity nylons,in contrast, the T_m and △H_f decrease obviously with increasing dosage. In this case, radiation cross-linking "freeze in" the pre-existing morphology, and then the prevention for reorganization duringheating is a dominant effect. The T_m from the second melting for all of the samples were depressed,corresponding with Flory theory. Therefore the crosslinks imposed on the molecules restrainedthe molecular mobility, and that not only depresses the crystallinity but also increases the imperfec-tion of crystallites when the radiated polymer melted and then recrystallized. These are also reflectedin the depression of heat and entropy of fusion as well as the appearance of double melting peakson the DSC thermograms.     

CHARACTERIZATION OF BRANCHING POINT DISTRIBUTION IN THE SOL OF IRRADIATED POLYSTYRENE WITH SEC-LALLS

In this paper, the change behavior of branching point distribution of irradiated polystyrene in sol has been first studied by the SEC-LALLS method. The experimental results show that branching parameter of the part with lower molecular weight in the sol changes little at the early stage of irradiation and that of the part with the higher molecular weight becomes greater with the increase in radiation dose.     

Fabrication of Zn-Ti layered double hydroxide by varying cationic ratio of Ti4+ and its application as UV absorbent

ZnTi-layered double hydroxides(LDHs) with varying Zn/Ti ratio have been synthesized by coprecipitation of zinc and titanium salts from homogeneous solution.The obtained ZnTi-LDHs possess high crystallinity and hierarchical structure with improved UV-absorbance property.The UV-vis spectra show that the UV absorbing properties of ZnTi-LDHs is stronger and broader than both MgAl-LDH and ZnAl-LDH due to the existence of Ti.Moreover,the UV absorption property increased with the content of Ti,which can be ascribed to the decrease in the band gap energy,as clearly confirmed by density functional theory calculations.When irradiated by UV rays,the property of the samples with generated free radicals(OH~·and O_2~·) was evaluated by means of electron spin resonance(EPR).ZnTi-LDHs generated a relatively lower active radicals in contrast with TiO_2 and ZnO,which implied an increased safety used as sunscreens.Therefore,this work provides a detailed understanding of UV shielding properties of ZnTiLDHs which was unrevealed previously,and demonstrates the expansive application prospects of ZnTiLDHs in the field of sunscreens.     

Fast heating in µ-thermal analysis</o:p>

Summary Thermal analysis of the 10 μm surface of materials using TA Instruments' μ-TA thermal probe and pulsed force mode AFM has shown promising results. This addresses the need of additional surface characterization based on principle of Thermal Analysis, which is complementary to other surface characterization techniques, i.e., Surface-IR, TOF-SIMS, etc. The method calls for identification of surface landscape by imaging first, followed by fast heating the spots of interest. The micro thermal probe is viewed to heat a small material with a tiny heater rather than to heat small material with a large heater in conventional thermal analysis. In this paper, we demonstrate the applicability in the adhesion temperature of the topical coatings of Tyvek? HDPE sheets, fusion of the heat-processed polyethylene fibers in a bundle, the surface crystallinity of PET pellets, and two examples of phase images of toughened Nylon 66. Comparisons were made where it is possible with standard thermal analysis techniques as well as with the microscopic techniques of AFM, TEM and optical.     

EFFECTS OF MOLECULE AGGREGATION STATE OF HINDERED PHENOL ON DYNAMIC MECHANICAL PROPERTIES OF CHLORINATED POLYETHYLENE*

Hindered phenol compound 3,9-bis{1,1-dimethyl-2[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80) is a polymorphous material with different physical structures. The initial AO80 is highly crystalline, whereas AO-80 obtained by cooling from its molten state is an amorphous material. Annealing treatment below the melting point of AO-80 results in structural development. The mixture of chlorinated polyethylene (CPE) and vitrified AO-80 particles exhibits a dramatic change in the dynamic mechanical properties during heat treatment at 130℃. This change can be attributed to the decomposition of the vitrified AO-80 particles and the hybridization of two constituents. The vitrified AO-80 particles can crystallize again in a CPE matrix by annealing at 100℃, but this crystal is different from that of the initial AO-80 in its microstructure. In addition, the incorporation of CPE chains caused a dramatic increase in the modulus. As a result, the AO-80 crystal particles that contain some CPE chains act as multifunctional crosslinks and the CPE/AO-80 hybrid was found to be a new type of elastomer.     

PHOTOINDUCED GRAFTING OF ACRYLIC AND ALLYL MONOMERS ON POLYETHYLENE SURFACE

Photoinduced grafting of acrylic and allyl monomers on polyethylene surface wasgenerally studied by using benzophenone (BP) as a photoinitiator. The grafting process wascarried out either in vapor-phase or in solution of the monomers. In the vapor-phase reactionwith a filter used to cut off the short wavelength UV light, allyl amine is the most reactive ofthe four monomers used and acrylic amide is comparatively more reactive than acrylic acid andallyl alcohol. Acetone, as a solvent and carrier for initiator and monomers, however, showsits reactivity to participate the reaction. The solution grafting with a filter is much faster thanthe corresponding vapor-phase reaction, and a fully covered surface by the grafted polymercan be achieved in this way.     

High damping and mechanical properties of hydrogen-bonded polyethylene materials with variable contents of hydroxyls: Effect of hydrogen bonding density

Hydrogen bonding is considered to have significant effect on the interaction between polymeric chains and on the viscoelasticity of the polymeric materials. In this paper, we attempt to discuss the relationship between hydrogen bonding density and damping behavior and mechanical properties of polyethylene-based polymeric materials. For this reason, a series of pendant chain hydrogen bonding polymers(PCHBP) with different hydrogen bonding density(HBD) were prepared by quantitatively changing the content of pendent hydroxyl groups on the main chain of polyethylene. It was found that PCHBP with low HBD showed similar properties to polyethylene, indicating that the property of the materials was dependent mainly on the structure of the main chain. However, PCHBP with high HBD exhibited two tanδ peaks and a platform of loss modulus as well as a high storage modulus(about 400 MPa) at the second tanδ peak temperature, demonstrating that a polymeric material with high strength and damping properties was obtained. More importantly, the maximum of loss modulus showed a linear increase with the HBD, indicating that a higher HBD greatly improved the damping properties of the polymeric materials.     

Effect of Binder on the Structure and Properties of Silicon Powder-supported TiO_2 Photocatalysis Material

Recoverable TiO2 photocatalysis material supported by silicon powder was prepared with sol-gel method, afterwards the silica gol and sodium silicate were used as molding binder respectively to investigate their effects （including binder type and binder addition quantity） on the crystal structure and catalysis properties of photocatalyst. In this work, the catalysis activity was defined as the degradation rate of methyl orange solution upon ultraviolet lamp irradiation, and the specific areas were determined with nitrogen desorption method. TiO2 crystal form was measured with X-ray powder diffraction and their micro-morphology was observed with SEM. Experimental results indicate that these two binders do not affect the crystal form transformation of TiO2, but silica gol can increase the specific surface area of TiO2 photocatalyst obviously and the addition of sodium silicate can decrease it. In all, silica gol is a better candidate than sodium silicate for higher catalysis property. In conclusion, 6% silica gol is the optimal addition concentration. Under this condition, the ratio of anatase to rutile TiO2 is 64：36, the specific area is 29.67 m^2/g, and as expected, the degradation rate of methyl orange could be as high as 90% after irradiation for 5 days.     

Application of electron diffraction in the structure characterization of polymer crystals

The dependence of properties on the structure and morphology of semicrystalline polymers offers an effective way to tailor the properties of these materials through structure control. To this end, establishing the structure and property relationship is of great importance. For a right characterization of the crystal structure, several techniques can be used. Among these techniques, electron diffraction has its advantage for determining the crystal structure related to specific formation condition since it can combine with bright and dark fields observation of the sample. This feature article describes the application of electron diffraction in determining the crystal structure of semicrystalline polymers with elaborately selected examples. We focus on how the electron diffraction can be used to disclose the crystal structure, mutual orientation of different crystals, as well as the disorders included in the polymer crystals.     

STUDY ON THE MODIFICATION OF POLY (METHYL METHACRYLATE) TRANSPARENT MATERIAL

A kind of transparent plastic material has been prepared with bulk copolymer of MMA-MA containing MA 20 vol% as matrix modified by introducing EtOH during bulk copolymerization to increase the transparency and by copolymerizing together with metallic salts of MA forming ionomer polymer to improve the heat-tolerance and hardness. The effect of the contents of the additives on the heat stability, hardness and transparency of the copolymer has been studied. The optical homogeneity of the copolymer material has also been examined. It has been found that the specific property of transparent material of this kind may be obtained by controlling the amounts of EtOH and metallic salt of MA.     

Layer-by-layer stacked graphene nanocoatings by Marangoni self-assembly for corrosion protection of stainless steel

Graphene nanosheets are widely used in anti-corrosion polymeric coating as filler,owing to the excellent electrochemical inertness and barrier property.However,as the arrangement of graphene nanosheets is difficult to form a perfect layered structure,polymeric coating with graphene nanosheets usually needs micron-scale thickness to ensure the enhancement of corrosion protection.In this work,layer-by-layer stacked graphene nanocoatings were fabricated on stainless steel by self-assembly based on Marangoni effect.The anti-corrosion property of graphene coatings were studied through Tafel polarization curves,electrochemical impedance spectroscopy and accelerated corrosion test with extra applied voltage.The self corrosion current density of optimized three-layered graphene coated sample was one quarter of that of bare stainless steel.And the self corrosion potential of optimized sample is increased to-0.045 V.According to the results,graphene nanocoatings composed of layered nanosheets exhibits good anticorrosion property.Besides,the self-assembly method provide a promising approach to make layeredstructure coating for other researches about 2 D material nanosheets.     

Microencapsulation of n-Eicosane as Energy Storage Material

For heat energy storage application, polynrea microcapsules containing phase change material, n-eicosane, were synthesized by using interfacial polymerization method with toluene-2,4-diisocyanate (TDI) and diethylenetriamine(DETA) as monomers in an emulsion system. Poly(ethylene glycol)octyl-phenyl ether (OP), a nonionic surfactant,was the emulsifier for the system. The experimental result indicates that TDI was reacted with DETA in a mass ratio of 3 to 1. FF-IR spectra confirm the formation of wall material, polyurea, from the two monomers, TDI and DETA.Encapsulation efficiency of n-eicosane is about 75%. Microcapsule of n-eicosane melts at a temperature close to that of n-eicosane, while its stored heat energy varies with core material n-eicosane when wall material fixed.Thermo-gravimetric analysis shows that core material n-eicosane, micro-n-eicosane and wall material polyurea can withstand temperatures up to 130, 170 and 250℃, respectively.     

Effect of Fumed SiO<Subscript>2</Subscript> on Pore Formation Mechanism and Various Performances of <Emphasis Type="Italic">β</Emphasis>-<Emphasis Type="Italic">i</Emphasis>PP Microporous Membrane Used for Lithium-ion Battery Separator

In this work,four samples containing different contents of fumed SiO2 were prepared to improve the pore size distribution and various properties of βnucleated isotatic polypropylene (β-iPP) biaxial membrane used for lithium-ion battery separator.The wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) results show that the fumed SiO2 promotes the formation of r-crystal slightly and narrows down the thickness distribution of β-lamellae;meanwhile,evenly distributed SiO2 within β-iPP can be inspected by scanning electron microscopy (SEM).Moreover,further detailed characterization of morphological evolutions during biaxial stretching by tensile testing and SEM manifests that SiO2 can strengthen β-iPP and make the samples deform more homogeneously,resulting in a gradually elaborate and finer oriented microfibril structure after longitudinal stretching,in which more uniform defects distribute between fibrils and restrain the formation of coarse fibrils effectively.Therefore,more superior microporous structure emerges with the addition of SiO2,accompanied by narrower pore size distribution and better connectivity between microvoids,which is confirmed by mercury porosimeter and diminished Gurley value.Moreover,the lower thermal shrinkage,decreased shrinkage rate and suppressed porosity reduction indicate that fumed SiO2 improves thermal and dimensional stability of membrane dramatically.Furthermore,due to the excellent wettability of SiO2 with electrolyte,the microporous membranes doped with SiO2 have higher electrolyte uptake,even after heat treatment at elevated temperature.