Agnesa Fiedlerová

Efficiency of Chemical Cross-Linking of Polypropylene

Abstract The efficiency of the chemical cross-linking of polypropylene was found to be dependent on the peroxide used (dicumyl peroxide, benzoyl peroxide, t-butyl peroxide, and t-butyl peroxy-benzoate). The reason for different cross-linking efficiency of peroxide and enhancement of the cross-linking efficiency of peroxide in the presence of polyfunctional monomer-penta-erythritol tetrallyl ether are discussed.

Photo‐Oxidation of sPP/Organoclay Nanocomposites

Photo‐oxidation of syndiotactic polypropylene–sPP/organoclay nanocomposites was performed. Nanocomposites were prepared in situ by melt compounding of sPP, compatibilizer (iPP grafted with maleic anhydride–iPP‐g‐MAN) and organoclay filler ME C18 (modified with octadecyl ammonium chains in intergaleries of layered silicate, of which silicate layers (about 1 nm thin) were exfoliated). The influence of ME C18 nanoparticles alone (in content region 1 to 15 wt%) and together with compatibilizer iPP‐g‐MAN on the photostability of the sPP nanocomposite was studied. It was found that the silicate ME C18 nanoparticles alone catalyze the photooxidation and shorten the induction period of photo‐oxidation to one fourth (at the content of 5 wt% of ME C18) in comparison with unfilled sPP) and the presence of compatibilizer supports the photo‐oxidation of sPP nanocomposite. The ME C18 nanoparticles decrease the efficiency of UV stabilizers. The rate of photo‐oxidation of sPP/clay nanocomposite after the induction period is significantly higher than unfilled sPP. The mechanism of photo‐oxidation is discussed.

Structure and properties of an interpenetrating polymer network-like system consisting of polystyrene-polyethylene: 1. Synthesis, elastomeric and thermoanalytical characterization

Abstract A polystyrene-polyethylene (PS-PE) interpenetrating polymer network (IPN)-like system was prepared by synthesis in situ. The system differs from ‘pure’ IPN systems in that the PS network is partially grafted onto the PE network. The mean molar mass of the polymer chain between two junction points ( M c ) was calculated from the values of uniaxial compression modulus. Differential scanning calorimetry and thermomechanical analysis measurements pointed to a considerable decrease of the crystalline phase in PE with increasing PS content. The melting temperature enhancement of the crystalline phase of PE is discussed.

Optical properties of IPN-like networks polyethylene/poly (butylmethacrylate-co-styrene) copolymer systems. III. Influence of copolymer crosslinkers

Abstract Poly[butylmethacrylate (BMA)- co -styrene(S)] copolymers and low-density polyethylene (PE) IPN-like networks were synthesized by a procedure described in earlier papers. Different molar BMA/S copolymer molar ratios starting from 50/50 up to 100/0 and a molar percentage of 1.0 of two copolymer crosslinkers, divinylbenzene and 1,4-butanedioldimethacrylate were used. The samples were analysed at room temperature (RT) by WAXS, swelling in CCl 4 and mechanical tests. Dynamic mechanical tests and optical investigations were performed in a temperature range between RT and 180°C. Both IPN types, at high copolymer BMA contents, showed a matching–mismatching optical transition of PE and copolymer refractive index with varying temperature. The type of the copolymer crosslinker influenced sensitively all the investigated properties.

Photo‐oxidation and Stabilization of sPP and iPP/Boehmite‐Disperal Nanocomposites

Photo‐oxidation studies on polypropylene (PP)/organoclay nanocomposites were performed. Nanocomposites of isotactic (iPP) and syndiotactic (sPP) polypropylene were prepared by melt compounding. The nanofiller was Boehmite Disperal OS2–alumina hydrates (Al(OH)O) modified by C10–C13 alkylbenzene sulfonic acid. The nanofiller content was 1, 5, and 10 wt%. There is a clear pro‐degradation effect of filler for both types of polypropylene used. The extent of this effect depends on the amount of filler and type of polypropylene used. In the case of sPP samples, the pro‐degradation effect is proportional to the amount of filler in the whole concentration range of filler content used. In the case of iPP, there is a pro‐degradation plateau at 5 wt% content of filler and higher concentration of filler (10 wt%) does not increase the rate and the course of photo‐oxidation. Two long term stabilizers of HAS family were tested ‐ commercial oligomeric stabilizer Chimassorb 944 (CHIM) and synthesized combined HAS/phenol (TMP). Stabilizing efficiency depends on the filler content. CHIM is able to stabilize just the nanocomposites with the lowest content (1 wt%) of filler. There is no stabilizing effect of this HAS in the case of the higher amount of nanofiller (5 and 10 wt%) in both types of polypropylene. By contrast, the combined HAS/phenol‐TMP revealed some stabilizing efficiency over the whole range of filler content. The possible reasons for this difference are discussed. Interactions of filler with some HAS stabilizers were studied in cyclohexane as a model liquid for polypropylene by UV‐spectroscopy. Interaction resulted in the fixing of additive on filler. Much stronger interaction has been obtained for oligomeric CHIM in comparison with low molecular HAS.

Structure and properties of an interpenetrating polymer network-like system consisting of polystyrene-polyethylene: 2. Electron microscopic investigation

Abstract Polyethylene-polystyrene (PEPS) interpenetrating polymer network-like materials with various ratios of PE/PS were prepared. A morphological study using a transmission electron microscopic technique showed that with increasing content of styrene in the system the frequency distribution of the diameter of PS particles becomes increasingly broader and a foam-like structure is formed. Contractions at polymerization and crosslinking as well as interfacial tensile forces are responsible for the IPN morphology.

Solid‐state polypropylene grafting as an effective chemical method of modification

The role of vinylidene groups, formed by the action of organic peroxides, on crosslinking reactions in isotactic polypropylene (iPP), is discussed. Grafting of polymerizable monomers on powdered iPP, performed below its melting temperature, occurs with high efficiency, depending on the structure of peroxide used.

PEROXIDE GRAFTING OF POWDERED POLYPROPYLENE BY BUTYL ACRYLATE

The efficiency of the grafting of powdered polypropylene (PP) by butyl acrylate (BA) initiated by tert.-butylperoxy-2-ethylhex-as a ratio of the grafted and polymerized monomer was relatively high during the whole course of the reaction and it does not decrease under 0.5. The relatively high polymerization rate and also grafting efficiency at the beginning of the reaction is refered to the gel effect - the monomer is absorbed in the amorphous part of the powdered PP. With increasing the content of monomer in the reaction feed, the content of unsoluble cross-linked polymer increased as the consequence of the radical cross-linking of polybutylacrylate chains. The mechanism of grafting of powdered PP by BA is discussed.

Degradation of Polypropylene Under the Effect of the Low-Molecular-Mass Organic Peroxides Below the Melting Temperature of the Polymer

Abstract The efficiency of five commercially available peroxides on the level of degradation of polypropylene (PP) at temperatures below its melting point has been studied. The efficiency extrapolated onto 100°C increases in the following order: tert. butylperoxy-2-ethyl-hexanoate ≈ tert. butylperoxy-isobutyrate <dilauroyl peroxide <1,1-bis(tert. butylperoxy)-3,3,5-trimethyl cyclohexane ≈ tert. butyl-perbenzoate. The various effects of peroxides on the degradation of PP is explained by different reactivity of primary radicals of the peroxides and their solubility.

IPN-like systems based on polyethylene and methacrylates

Abstract Interpenetrating polymer networks (IPNs) based on polyethylene (PE) and poly(methacrylate)s were prepared by in situ polymerization. A co-continuous phase morphology was obtained. The use of dodecyl methacrylate produces good compatibility between PE and poly(methacrylate)s. The degree of PE crosslinking in IPNs has been estimated by comparison of the melting temperatures of PE crystallites in pure crosslinked PE with those in IPNs.