Alina Kamińska

The influence of side groups and polarity of polymers on the kind and effectiveness of their surface modification by air plasma action

The changes of contact angle (θ) and surface free energy (γS) under low-temperature air plasma in the polymers of different chemical structure and polarity (polyethylene, PE; polypropylene, PP; poly(ethylene terephtalate), PET and poly(methyl methacrylate), PMMA) pointed out to the greater effect of short-time plasma action (5–15 s) on these parameters as compared to longer times of exposure. The non-reversion effect of θ changes caused by plasma in PE and PP suggests that the oxidation processes mainly decide about values in nonpolar polymers. The significantly greater θ changes in PE than those in PP indicate that the side groups present in the main chains impede oxidation of such a polymer by plasma. The reversion of θ changes in PET and in PMMA, and return of these values to almost the initial ones after 10 min storage proves that the main reason for θ changes in polar polymers is a certain alteration of the chain conformation. These changes, taking place after longer plasma treatment, suggest that the side ester groups in PMMA retard the above-mentioned conformational transformations. Then, in both kinds of polymers (polar and nonpolar) the structure of macrochain decides about the efficiency of reaction caused by plasma, and at the same time the side groups retard not only the oxidation processes but the conformational changes as well.

THERMAL HELIX-COIL TRANSITION IN UV IRRADIATED COLLAGEN FROM RAT TAIL TENDON

The thermal helix-coil transition in UV irradiated collagen solution, collagen film and pieces of rat tail tendon (RTT) were compared. Their thermal stabilitys were determined by differential scanning calorimeter (DSC) and by viscometric measurements. The denaturation temperatures of collagen solution, film and pieces of RTT were different. The helix-coil transition occur near 40 degrees C in collagen solution, near 112 degrees C in collagen film, and near 101 degrees C in pieces of RTT. After UV irradiation the thermal helix-coil transition of collagen samples were changed. These changes depend on the degree of hydratation.

Photooxidative degradation of poly(alkyl methacrylate)s

Photooxidative degradation of four different poly(alkyl methacrylate)s: poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate), poly(n-butyl methacrylate) and poly(n-hexyl methacrylate) have been investigated using FTIR, UV–Vis spectroscopy and gel permeation chromatography. The influence of the ester group size on the course of photochemical reactions in poly(alkyl methacrylayte)s has been estimated. It has been found that PMMA undergoes slower photooxidation but faster photodegradation than those in higher poly(alkyl methacrylate)s. The different behavior of the polymers studied is caused by the different reactivity of the macroradicals influenced by the different flexibility and mobility of macrochains at room temperature.

Study of poly(acrylic acid)–poly(vinylpyrrolidone) complexes and their photostability

Abstract The poly(acrylic acid)(PAA)–poly(vinylpyrrolidone) (PVP) complexes with different stoichiometric ratio were obtained from aqueous solutions at different concentrations and pH values. The structure of complexes in solutions and in solid state has been studied using mainly FTIR spectroscopy. Least-square curve fitting method has been applied to calculate the contribution of different types of carbonyl groups (free and hydrogen bonded) in the PAA/PVP mixtures. Both polymers and their blends at different compositions were UV-irradiated (λ=254 nm ) in air. It has been found that PAA/PVP complexes are generally more photostable than pure polymers. This stabilisation effect was explained by the high amount of intermolecular hydrogen bonds reinforcing the polymer structure. Photocrosslinking is an additional factor influencing the stability of PAA/PVP complexes.

Modification of polystyrene and poly(vinyl chloride) for the purpose of obtaining packaging materials degradable in the natural environment

Abstract For the purpose of increasing degradability of polystyrene (PS) and poly(vinyl chloride) (PVC), they were modified by means of introducing 1–5% addition of ketone (acetophenone or benzophenone). The influence of UV radiation on thin films of polymers modified in this way was studied. The changes in chemical structure of PS and PVC were studied using UV–vis and FTIR spectroscopy, the degradation reactions were monitored by determining the average molecular weights and polydispersity by gel chromatography, and the crosslinking reactions were estimated by determining the weight content of insoluble gel. The mechanical properties were studied by using standard tensile testing measurements. It was found that the ketones used, acting as sensitizers and/or initiators, caused some considerable changes of photochemical stability of both polymers. The oxidative photodegradation of PS, carried out in the same conditions and presence of the same quantity of modifying additives, is accelerated by a considerably higher rate in comparison to the analogous processes occurring in PVC. The differences in the course of photochemical processes of both irradiated polymers are related to the different miscibility of components. At the same time the limited efficiency of photocrosslinking and only slight deterioration of mechanical properties in PS with added acetophenone or benzophenone suggest the possibility of using such compositions for the manufacture of plastics degradable in natural environment.

Photo-oxidative degradation of some water-soluble polymers in the presence of accelerating agents

The unsolved problem of plastic waste utilization has led to a great interest in the development of studies of accelerated degradation of polymers. In this work the course of photo-oxidative degradation of some water soluble polymers such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA) and poly(vinylpyrrolidone) (PVP) in the presence of hydrogen peroxide has been investigated. The following methods have been applied: viscometry, IR and UV-Vis spectroscopy, gel permeation chromatography and chemical analysis. The hydrogen peroxide is an unstable compound which undergoes photolysis upon UV irradiation. Free radicals (HO and HO 2 ) formed in this process are efficient initiators of polymer degradation. The changes of the viscosity and the average molecular weight indicate that the rate and efficiency of photodegradation of PAA, PMA and PVP in the presence of H 2 O 2 is much higher in comparison with respective values obtained in the absence of this agent. Spectroscopic data show that some simultaneous competitive processes (degradation, oxidation and chromophores formation) take place in UV irradiated polymers. In PAA photocrosslinking reaction occurred. The efficiency of this reaction was estimated by the amount of formed insoluble gel. Contrary to degradation, photocrosslinking of PAA was hampered by H 2 O 2 , It was found that photochemical reactions in polymers depend on the concentration of H 2 O 2 and dose of UV irradiation. The mechanisms of reactions occurring in the studied systems have been discussed. Moreover, the influence of the chemical structure of macromolecules on the course of photo-oxidative degradation has been considered. It has been also shown that acceleration of PVP photodegradation by H 2 O 2 is larger than that by FeCl 3 . Some additional data indicating the changes of physical properties of photodegraded polymers have been presented. It can be concluded that hydrogen peroxide may significantly accelerate the decay of water soluble polymers present in municipal sewers.

Photoinitiated degradation of polystyrene in the presence of low-molecular organic compounds

Abstract The influence of low-molecular organic compounds such as benzophenone (BPh), anthraquinone (AQ) and benzoyl peroxide (BPo) on the phototransformations of polystyrene has been investigated. The viscometry, gravimetry, infrared and UV–vis spectroscopy has been used in these studies. The results indicate that additives applied accelerate and increase the efficiency of photodegradation, photodestruction and photo-oxidation processes in polystyrene but they hamper the photocrosslinking and formation of the double bonds in this polymer. In all these processes, BPh showed the greater activity as photoinitiator comparing to AQ and BPo.

The influence of transition metal salts on photo-oxidative degradation of poly(ethylene oxide)

Abstract The influence of iron (III), cobalt (II) or nickel (II) chlorides on photo-oxidative degradation of poly(ethylene oxide) (PEO) has been investigated. The rates and efficiencies of photochemical reactions occurring in PEO containing small amounts (1–3%) of the transition metal chlorides were compared. The mechanism of reaction induced by UV-irradiation in doped PEO is discussed. The role of active Cl atoms and chlorine radical anion Cl 2 − (formed in the first step of metal salt photolysis) in initiation of polymer degradation is pointed out. The iron salt was found to be the most effective agent accelerating PEO photodegradation.

The effect of UV radiation on the values of thermal parameters of collagen containing β-carotene

Abstract Thermal parameters of collagen containing β-carotene before and after UV irradiation were determined in air and nitrogen atmospheres. It was found that after UV irradiation of collagen and collagen containing β-carotene, mass decrement, activation energy and entropy changes were changed and may give information about the phototransformations which occur in this protein. However, these processes do not affect distinctly the values of onset temperatures. Comparison of the derivatographic curves in air and in nitrogen suggests that oxidation of collagen may occur during heating of this protein and that this may also occur under UV irradiation. Smaller changes in the presence of β-carotene suggest that it makes collagen more resistant to the action of UV radiation. ©

Photo-oxidative degradation of poly(ethylene oxide)-copper chloride complexes

Abstract Poly(ethylene oxide) (PEO) forms with CuCl 2 a complex in acetonitrile (AN) solution as well as in solid phase (after evaporation of solvent). During u.v. or visible light irradiation it has been observed that a rapid photo-oxidative degradation of the PEO-CuCl 2 complex in AN is caused by free Cl ● and/or Cl ●− 2 radicals (formed from the photolysis of CuCl 2 ). With increasing degradation processes, there is also a pronounced change in the morphology of PEO-CuCl 2 complexes. They lose their capability to form spherulites. This results from changes in molecular weight and dispersity that affect crystallization conditions. Both wide angle X-ray spectroscopy and differential scanning calorimetry show that photodegraded PEO molecules are almost amorphous. Low-molecular fractions are formed as a result of chain scission processes. Photodegradation processes in AN solution do not cause crosslinking or formation of a gel fraction.