Study of the dielectric relaxation of poly(phenylpropyl acrylate) and poly(phenylpropyl methacrylate): effect of slight differences in chemical structure

A comparative study of the dielectric relaxational behaviour of two structurally close polymers, containing aromatic side groups, was carried out in order to analyse how slight differences in the chemical structure affect the molecular responses to perturbation field. Specifically, poly(phenylpropyl acrylate) (P3Ph1PA) and poly(phenylpropyl methacrylate) (P3Ph1PM) were studied using differential scanning calorimetry and dielectric relaxation spectroscopy in the frequency range 10^?2–10⁶ Hz and temperature window of ?80 to 120 °C. Both techniques show one glass–rubber transition for P3Ph1PA and two for P3Ph1PM, which evidence the great effect of the methyl groups on the segmental motions of the polymer. Phenomenological analysis of the data was carried out in order to establish the strength, width and fragility parameters of the glass–rubber transitions. In the case of P3Ph1PA, the strength is found to be larger than for P3Ph1PM, pointing out that the methyl group disturbs the mobility. Conductive processes dominate the dielectric spectra at high temperatures and low frequencies. © 2015 Society of Chemical Industry     

Amphiphilic 2‐ethyl hexyl methacrylate‐b‐N,N′‐dimethylacrylamide diblock copolymer monolayer behaviour at the air − water interface†

The surface activities of two amphiphilic diblock copolymers containing 2‐ethyl hexyl methacrylate‐b‐N,N′‐dimethylacrylamide (EHMA‐b‐DMA) possessing hydrophobic segments of different chain lengths were studied. Toward this end, surface pressure?area (π?A) isotherms, static and dynamic elasticities and the ν exponent of the excluded volume of polymers forming monolayers at the air?water interface were measured. The degree of hydrophobicity of the diblock copolymers was estimated by determining their surface energy values from contact angle measurements. The morphology of the monolayer at different surface pressures was studied by Brewster angle microscopy. Both copolymers were observed to form stable and elastic monolayers, and their collapse was observed to occur at similar surface pressures. Langmuir?Blodgett films were successfully deposited onto mica and silicon wafers and analysed by atomic force microscopy. © 2014 Society of Chemical Industry     

Microencapsulation of lycopene by spray drying: Characterization, stability and application of microcapsules

Microencapsulation can be an alternative to minimize lycopene instability. Thus, the aim of this study was to microencapsulate lycopene by spray drying, using a modified starch (Capsul^®) as an encapsulating agent, and to assess the functionality of the capsules applying them in cake. The quantity of lycopene was varied at 5, 10 and 15% in a solution containing 30% of solids in order to obtain the microcapsules. These microcapsules were evaluated as to encapsulation efficiency and morphology and then submitted to a stability test and applied in cakes. Encapsulation efficiency values varied between 21 and 29%. The microcapsules had a rounded outer surface with the formation of concavities and they varied in size. The stability test revealed that microencapsulation offered greater protection to lycopene compared to its free form and it was observed that the microcapsules were able to release pigment and color the studied food system in a homogenous manner.     

Impact of moisture and plasticizer properties on polymer–plasticizer physical mixing performance

The ability for polymers and additives to physically mix in many industrial applications is dictated by a combination of kinetic and thermodynamic factors. The presence of moisture may complicate the mixing performance as water can interact at various degrees with each of the components; this depends on the hydrophilicity of the materials. In this study, the physical mixing behavior of a ternary system consisting of a hygroscopic polymer (copovidone), a plasticizer, and water was examined. Three different liquid plasticizers with a range of hydrophilic–lipophilic properties and viscosities were evaluated for their physical mixing performance and the impact of their water content. Inverse gas chromatography was introduced as a new method for measuring the surface characteristics of the physical mixtures to quantify the mixing performance. Through the application of the Flory–Huggins model to understand the thermodynamic behavior of the system, it was shown that mixing was less effective in a system of high water content for a hydrophobic plasticizer. However, the underlying thermodynamic unfavorability of such a system could be overcome by kinetic influence to provide a good mixing performance. Specifically, as the viscosity of the plasticizer decreased, the influence of the thermodynamic characteristics was found to become less apparent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41679.     

Interaction of dendronized polymeric nanocomposites with isomeric cyclohexanediols

Dendronized poly(diethylaminoethyl methacrylamide) (PEAM) was studied in blends containing isomeric cyclic dialcohols. Monomers and polymers were characterized by spectroscopic measurements. The phase behaviors of blends of PEAM with 1,2‐, 1,3‐ and 1,4‐cyclohexanediols (1,2‐CHD, 1,3‐CHD and 1,4‐CHD, respectively) were established. Transparent films of the blends exhibited a single glass‐transition temperature (T_g). Thermogravimetric analysis (TGA) revealed the temperature at which the polymer releases the small molecules. UV‐vis spectra of 1,3‐CHD and 1,4‐CHD derivatives showed an isosbestic point that indicated the association of the alcohols. FT‐IR measurements showed shifts in several absorption bands. The results were analyzed in terms of the side‐chain structure and the interactions involved. AFM measurements revealed differences between the polymer and the blends. Compatibilization of blends of PEAM/CHDs occurred via the formation of hydrogen bonds, although hydrophobic interactions could not be disregarded. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42267.     

Evaluation of new chemically modified coconut shell adsorbents with tannic acid for Cu (II) removal from wastewater

The adsorption of Cu (II) from aqueous solutions using coconut shell modified powder was investigated in batch experiments. The surface charge of the adsorbent was determined. The points of zero charge (PZC) of the adsorbents (pH_PZC) were 4.5, 2.0, and 2.0 to raw coconut (RC), raw coconut alkalized (RCA), and coconut shell modified with tannic acid (TCA) adsorbent, respectively. Batch experiments were performed under kinetic and equilibrium conditions. The kinetic data were analyzed using a pseudo second‐order, and Elovich equation. Adsorption equilibrium data were investigated using the Langmiur, Freundlich, Temkin, and Dubinin–Raduschevich (D–R) isotherm models. It has been found that chemically modified coconut shell (TAC) affected performance when compared with unmodified coconut shell (RC). Kinetic studies showed that the adsorption followed a pseudo‐second‐order rate model. Biosorption kinetics of Cu(II) on the adsorbent TCA was rapid such that almost 90% of Cu(II) were adsorbed within 80 min. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40744.     

Anodic porous alumina structural characteristics study based on SEM image processing and analysis

The present work reports the porous alumina structures fabrication and their quantitative structural characteristics study based on mathematical morphology analysis by using the SEM images. The algorithm used in this work was implemented in 6.2 MATLAB software. Using the algorithm it was possible to obtain the distribution of maximum, minimum and average radius of the pores in porous alumina structures. Additionally, with the calculus of the area occupied by the pores, it was possible to obtain the porosity of the structures. The quantitative results could be obtained and related to the process fabrication characteristics, showing to be reliable and promising to be used to control the pores formation process. Then, this technique could provide a more accurate determination of pore sizes and pores distribution.     

Modification of the air–water interface by a chitosan adsorption process. Effect on an amphiphilic polymer monolayer

Monolayer formation by poly[(maleic anhydride)‐alt‐(stearyl methacrylate)] (MA‐alt‐StM) on aqueous subphases, with and without chitosan, was studied by the Langmuir technique. Chitosan (CS) modified considerably the shape of the MA‐alt‐StM isotherms on water. To explain this behavior, the surface activity properties of chitosan at the air–solution interface were studied. The variations of the interfacial tension, γ_int, with chitosan concentration and temperature, were also determined. The results were discussed in terms of the modification of the air–water interface owing to the presence of chitosan in the subphase and the surface activity. It was found that the standard free energy of adsorption, , values were dependent on the degree of acetylation (DA) over the DA range being studied. Copyright © 2004 Society of Chemical Industry     

Viscoelastic relaxations in poly(dimethylphenyl methacrylates)

Summary Dynamic mechanical properties of poly(dimethylphenyl methacrylátes) were studied considering the different positions of the methyl groups on the phenyl ring. In all cases a clear relaxation can be observed which is associated to the polymer glass transition temperature (Tg). Nevertheless, at lower temperatures, viscoelastic activity is negligible. A correlation between the steric hindrance due to the methyl groups and the temperature at which the relaxation is detected, was established.