Konrad Szustakiewicz

Comparative study on flame, thermal, and mechanical properties of HDPE/clay nanocomposites with MPP or APP

The article reports on flammability, thermal, and mechanical properties of bimodal high-density polyethylene/clay nanocomposites modified with ammonium polyphosphate or melamine polyphosphate (MPP) flame retardants. Two types of clays were used as fillers for the composites—the first one was standard montmorillonite modified with quaternary ammonium salt (ZR2), and the second one was montmorillonite modified with aluminium hydrogen sulfate (ZG1). As a compatibilizer, maleic grafted polyethylene (Plb) was used. X-ray diffraction and transmission electron microscopy were used to characterize the layer structure of clays in the composites. The limiting oxygen index tests showed synergistic effect between both clays and MPP. Flammability was also examined using cone calorimetry technique. The influence of all the fillers on thermal stability (thermogravimetric analysis), crystallinity (differential scanning calorimetry and wide angle X-ray scattering techniques), and mechanical properties was also studied.

Excimer laser-induced incubation of poly(L-lactide)

The irradiation of polylactide by KrF excimer laser with subthreshold fluence results in modification of its properties via photochemical reactions. A common approach is to modify chemical composition of polymer surface by UV irradiation, for example, in order to improve their wetting properties. In this paper, authors present a possibility of bulk modification of poly(L-lactide) which is related to photofragmentation and creation of new terminal groups. The irradiation results in decrease of molecular weight and increase of polydispersity. The appearance of new terminal groups is responsible for enhancement of absorption in UV-C range. The intensity of chemical composition changes introduced by UV irradiation can be precisely dosed thanks to a pulse character of laser source. Modifications can be controlled during the process by the analysis of energy transmitted through a polymer sheet. The distribution of absorption coefficient changes along with the depth of irradiated polymer and its correlation with polydispersity was discussed. Presented technique can be used for selective and controllable modification of hydrolytic degradation time of biodegradable polyesters utilized in biomedical applications.

Effect of CO2 laser micromachining on physicochemical properties of poly(L-lactide)

In this paper, we present some examples of micromachining of poly(L-lactide) with a CO2 laser and an analysis of changes in material properties in the heat affected HAZ induced by the fluence well above the ablation threshold. The complexity of the processes of decomposition implies the need for simultaneous use of many selective analytical techniques which complement each other to give a full image of the changes. Introduced changes were characterized using Differential Scanning Calorimetry (DSC), Gel Permeation Chromatography (GPC), X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR). It turns out that CO2 laser processing of poly(L-lactide) mainly induces surface changes. However, oxidation of the surface was not observed. We recorded a bimodal distribution and some reduction in the molecular weight. Infrared spectroscopy in turn revealed the existence of absorption bands, characteristic for the vinyl groups (RCH=CH2). The appearance of these bands indicates that the decomposition of the polymer occurred, among others, by means of the cis-elimination reaction.

Degradation of poly(L-lactide) under femtosecond laser treatment

In this paper, for the first time, we present an analysis of changes of physicochemical properties of poly(L-lactide) induced by the femtosecond laser. Introduced changes were characterized using Differential Scanning Calorimetry, Gel Permeation Chromatography, X-ray Photoelectron Spectroscopy and Fourier Transform Infrared spectroscopy. We have noted that even for these process parameters for which no thermal ablation effects occurred, we observed some changes in material properties. In GPC image we recorded an increase in polydispersity index and some reduction of the molecular weight. The FTIR spectra show a reduction in the number of both C=O and C−O−C bonds in the polymer as well as the appearance of new bands. By using the XPS it was determined that processing with femtosecond laser cause a small oxidation of the surface layer. Decay of the spectra indicates the possibility of carboxyl (−COOH) and hydroxyl (−OH) groups present in the modified polymer. Although the observed changes are relatively small compared to long pulse duration lasers or UV lasers, they cannot be neglected in biopolymer applications for tissue engineering.

The influence of ArF excimer laser micromachining on physicochemical properties of bioresorbable poly(L-lactide)

The main advantage of laser processing is a non-contact character of material removal and high precision attainable thanks to low laser beam dimensions. This technique enables forming a complex, submillimeter geometrical shapes such as vascular stents which cannot be manufactured using traditional techniques e.g. injection moulding or mechanical treatment. In the domain of nanosecond laser sources, an ArF excimer laser appears as a good candidate for laser micromachining of bioresorbable polymers such as poly(L-lactide). Due to long pulse duration, however, there is a risk of heat diffusion and accumulation in the material. In addition, due to short wavelength (193 nm) photochemical process can modify the chemical composition of ablated surfaces. The motivation for this research was to evaluate the influence of laser micromachining on physicochemical properties of poly(L-lactide). We performed calorimetric analysis of laser machined samples by using differential scanning calorimetry (DSC). It allowed us to find the optimal process parameters for heat affected zone (HAZ) reduction. The chemical composition of the ablated surface was investigated by FTIR in attenuated total reflectance (ATR) mode.

Laser micromachining and modification of bioabsorbable polymers

In this research the influence of laser micromachining on physicochemical properties of bioabsorbable polymer was investigated. Poly(l-lactide) (PLLA), commonly used for manufacturing non-permanent biomedical devices, was irradiated with varying fluences by CO2 laser and by KrF excimer laser. To evaluate modification of the material, several analytical techniques were used: ATR (attenuated total reflection), XPS (X-ray photoelectron spectroscopy) and DSC (differential scanning calorimetry). We found that the laser-affected material has lower glass transition (Tg) and melting (Tm) temperatures. CO2 and KrF excimer lasers can be successfully used for cutting and drilling of polylactide.