Jolanta Kowalonek

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.

Surface modification of thin polymeric films by air-plasma or UV-irradiation

Abstract Commercial, purified poly(vinyl chloride) (PVC) in a form of thin film was used for modification by low-temperature air-plasma or short-wavelength UV-irradiation. The changes of surface properties were monitored by contact angle measurements allowing for calculation the surface free energy as well as its polar and dispersive components. Both modification sources cause surface oxidation of PVC films, which is connected with formation of functional groups enhancing polymer wettability. This process is very fast and efficient in air-plasma but slower during PVC exposure to UV. Storage of modified PVC indicates that in plasma also conformational changes occur. In case of UV-irradiated PVC secondary, dark reactions (mainly oxidation) take place during storage at ambient conditions.

The influence of UV-irradiation on poly(vinyl chloride) modified by iron and cobalt chlorides☆

Abstract The influence of ultraviolet radiation ( λ =254nm) on thin PVC films modified by addition of 1–5%(wt.) iron (III) chloride or cobalt(II) chloride is reported. The photoinduced degradation, oxidation and dehydrochlorination were studied using Gel Permeation Chromatography, viscometry, UV-Visible and FTIR absorption spectroscopy. The photocrosslinking yield was estimated by separation of insoluble gel. Sample morphology was observed by optical microscopy. It was found that both salts change the course of photochemical reactions in PVC. These changes depend on salt type and content as well as on time of UV-irradiation. FeCl 3 and CoCl 2 hinder main chain scission in PVC in the initial stage of irradiation (after 1 h) but accelerate this reaction during prolonged exposure (10–30 h). Photodehydrochlorination is retarded in doped PVC (with the exception of PVC+1%CoCl 2 ). PVC photocrosslinking is less efficient in the presence of additives after longer period of degradation. The influence of salts on photooxidation is different—Fe chloride slightly decelerates whilst Co chloride accelerates the formation of carbonyl groups in PVC. The differences of both salts on photooxidative degradation in PVC are caused by their varying chemical nature and by differences in sample morphology.

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.

Thermogravimetric analysis of thermal stability of poly(methyl methacrylate) films modified with photoinitiators

Films of poly (methyl methacrylate) (PMMA) were prepared by the addition of photoinitiator to the polymer. The influence of five organic photoinitiators on thermal stability of poly(methyl methacrylate) was studied by thermogravimetric analysis. Next, the PMMA films doped with these photoinitiators were UV irradiated and investigated in terms of changes in their thermal stability. It was found that the photoinitiators had accelerated thermal degradation of non-irradiated PMMA films due to the action of free radicals coming from the additives’ thermolysis. For UV-irradiated specimens, the effect of photoinitiator on PMMA thermal stability depended on the chemical structure of organic compound modifying the polymer. In general, thermal stability of irradiated samples was higher in the presence of additives. Thermal destruction of modified PMMA can be explained by the formation of resonance structures in aromatic photoinitiators and consumption of energy in dissipation processes.

Changes of poly(ethylene oxide) photostability by doping with nickel(II) chloride

Abstract The influence of small addition of nickel(II) chloride on photooxidative degradation of poly(ethylene oxide) (PEO) in solution and in solid state has been investigated. Gel permeation chromatography, viscometry, differential scanning calorimetry, infrared and UV–Vis absorption spectroscopy has been used in these studies. It was found that nickel salt accelerates photodegradation and photooxidation of PEO. Photoinduced changes of PEO crystallinity and influence of macrochains conformation on the efficiency of photodecomposition has also been discussed.

The influence of UV-irradiation on chitosan modified by the tannic acid addition.

The influence of UV-irradiation with the wavelength 254 nm on the properties of chitosan modified by the tannic acid addition was studied. Tannic acid was added to chitosan solution in different weight ratios and after solvent evaporation thin films were formed. The properties of the films such as thermal stability, Young modulus, ultimate tensile strength, moisture content, swelling behavior before and after UV-irradiation were measured and compared. Moreover, the surface properties were studied by contact angle measurements and by the use of atomic force microscopy. The results showed that UV-irradiation caused both, the degradation of the specimen and its cross-linking. The surface of the films made of chitosan modified by the addition of tannic acid was altered by UV-irradiation.

Studies of chitosan/pectin complexes exposed to UV radiation

Chitosan and pectin form complexes owing to electrostatic interactions between positively charged amino groups in chitosan and negatively charged carboxylate groups in pectin, which was confirmed by ATR-FTIR spectroscopy and contact angle measurements. Moreover, the formation of these complexes might be associated with the loss of the biopolymers ordering, which resulted in higher surface roughness and lower thermal stability of the complexes in comparison to those of homopolymers. UV rays, used as a sterilizing agent, caused a moderate increase in the surface polarity of the complexes. Roughness parameters of these samples changed irregularly after irradiation, and their thermal stability was slightly affected by UV rays. The results indicated that the complexes studied appeared to present resistance to UV action higher than homopolymers, which is a desirable property in medical or pharmaceutical applications.

New piezoelectric composites based on isotactic polypropylene filled with silicate

Polymeric cellular composites are very important materials in modern electronics because they can be used as piezopolymers due to low specific weight, good thermal resistance and high value of piezoelectric constant d33. The aim of this work was to obtain and characterize the cellular polypropylene (PP) composites as materials designed for microelectronics. PP has been modified by addition of commercial silicate filler and the obtained materials were extruded. Then, the composites were subjected to electric field for polarization. Effect of the filler content on the structure and physicochemical properties of the composites have been investigated. The following experimental methods have been applied: SEM, XRD, thermogravimetry, tensile tests and measurements of voltage and electric charge accumulated in the polymer. The piezoelectric constant and stability of piezoelectric properties were also determined. It was found that the growth in the filler content in the polymer causes the increase in the film porosity and the degree of PP crystallinity that reaches 70% for the PP sample with 10% of the filler. Young’s modulus increased also in the presence of the filler. Moreover, the thermal stability of the composites was improved compared to neat PP. The piezoelectric constant of the composites was about 200 pC/N).

Accelerated Degradation of Polymers

Abstract Application of photochemical processes for the environment protection against plastic waste has been shown in this communication. The ways of acceleration of decomposition of high molecular compounds including the effect of UV-radiation, metal salts and hydrogen peroxide are shown. The results of photo-oxidative degradation of selected commercial polymers using IR, UV-Vis spectroscopy, viscometry, gel permeation chromatography and optical microscopy has been presented.