The change in the main power parameters of poly(methyl methacrylate) ablation by continuous-wave CO2 laser radiation has been studied. Measurements of the complex parameter “target weight + recoil force of ablation flow” were carried out using a force meter with computer data recording having a time resolution of 126.5 ms. Experimental data for the initial interval of 0–2 s were approximated by a model function, the processing of which made it possible to identify changes in the target weight and the recoil force of the ablation flow during irradiation. For the moment the ablation rate reaches a stationary regime, the energy efficiency of the process in a low-thrust jet engine was determined to be Cm = 115 μN/W, which decreases over time of laser irradiation due to the formation of a crater with a concave surface and an increase in gas pressure in the ablation chamber. It is noted that the type of ablation curve and, accordingly, an approximating function for the initial stage of ablation are individual for each polymer and laser beam parameters.

The surface of chemically modified polytetrafluoroethylene, obtained by introducing 1 mol % perfluoropropyl vinyl ether in the polytetrafluoroethylene macromolecule chain, has been studied using Raman spectroscopy. Three conventional zones with varying degrees of modification are distinguishable on the surface, and the spectrum of the ablation crater is fundamentally different from that of the pristine polymer. The crater spectrum, showing a general rise in the baseline, exhibits new bands due to both double carbon bonds and absorption bands of CF3 groups. A key factor in the laser ablation process is the influence of defects in the regular structure of polymer macromolecules, both intrinsically present in the polymer and induced by laser irradiation.

The formation of laser thrust by the pressure of gases released from the crater of laser ablation of polytetrafluoroethylene in vacuum has been studied, and a model for calculating the mechanical recoil impulse of ablation products has been implemented on the basis of a gravimetric curve obtained using an electronic balance that allows direct recording during intermittent (at 5-s intervals) or continuous irradiation for 5, 10, 15, 25, and 30 s with an infrared CO2 laser. Regardless of the laser operation mode, the observed polymer weight loss by ablation is linearly related to the laser irradiation time, having a rate of 80 μN/s. The maximum mechanical recoil impulse, which appears on the gravimetric ablation curves 4.5 ± 0.3 s after the laser is switched on, is 145 ± 7 or 90 ± 20 μN s in the continuous or the intermittent irradiation mode, respectively. In this case, an increase in the time of laser irradiation of the polymer in both modes leads to an insignificant change in the specific mechanical recoil impulse within 2.76 ± 0.06 μN/J. The results of the study show the possibility of using a polytetrafluoroethylene target for laser thrust, and the method of calculating the force momentum from the gravimetric curve of ablation of polytetrafluoroethylene can be used to investigate the mechanism of laser ablation of other polymer targets.

The irradiation of a poly(vinylidene fluoride) (PVDF) plate with γ-rays up to 100 kGy leads to the breaking of the chain and the formation of unsaturated bonds but practically does not have any effect on the conformation composition of PVDF macromolecules. The main conformer, as in native PVDF, is the β form. Irradiation with an IR laser leads to a noticeable carbonization of PVDF macromolecules and is accompanied by a structural transition of polymer macromolecules from the β conformer to the α conformer. In the IR spectrum of the powdered product from laser ablation of PVDF, in addition to the absorption bands of the ablation crater, absorption bands from the parent PVDF are still present.

Irradiation of polyamide-6 (PA) with γ-rays reduces its resistance to subsequent IR laser radiation. The average rate of laser ablation of PA, preliminarily irradiated with γ-rays at a dose above ~300 kGy, is almost dose-invariant and is 30% higher than that of the initial unirradiated polymer. The pattern of the dose dependence of the laser ablation rate for the samples pre-irradiated with a dose of 3.24 MGy at a dose rate of 4.2 Gy/s is mixed in character, varying from the shape characteristic of the initial polymer at the initial stage to the shape typical of the maximum radiation dose in the stationary laser ablation mode. One of the products of PA laser ablation is a dispersed polymer, consisting of nano- to micrometer-sized particles, the size range of these particles shifting toward smaller values with an increase in the γ radiation dose, a trend that is explained by a decrease in melt viscosity.

The effect of preliminary γ-irradiation on accelerating the speed of laser ablation of a polyamide is measured for the first time. A linear increase of intensity with a rate of 0.15 mg/s is observed during laser ablation of the polyamide pre-irradiated with γ-rays at a dose of 3,500 kGy. A γ-radiolysis dose of 10 – 20 kGy causes extreme changes in the molecular-topological parameters and the maximum level of growth of the rate of laser ablation. Thus pre-irradiation with γ-rays may be used to optimize the laser ablation of the polymer.

We report the effect of preliminary γ-irradiation of polyethylene (PE) and ethylene-propylene copolymer (CEP) on the kinetics of polymer ablation under CO2 laser irradiation. The rate of PE ablation exceeds the rate of CEP ablation at all doses of γ-irradiation. The ablation rate of the polymers can be approximated by a linear function in the initial stage, and the rate reaches a constant value in the second stage of ablation. The rate of laser ablation increases linearly with the dose of preliminary γ-irradiation in both stages of the kinetics. For PE ablation, the duration of the linear increase in rate decreases with increase in preliminary radiolysis dose. The morphology of the crater surface formed during the laser ablation of γ-irradiated polymers is characterized by a more diverse structure.

We study the effect of γ-radiation from 60Co on the rate of post-irradiation laser ablation of polyvinylidene fluoride (PVDF). The laser ablation of both the initial and γ-irradiated polymer occurs without an incubation period and does not require time to heat up the polymer target by the laser within the time scale of our measurements. The second feature of the laser ablation of PVDF is an extreme dependence of the ablation rate on the dose of γ-radiation over a wide range (10 kGy – 3.5 MGy) and the appearance of a minimum ablation rate of 0.1 mg/s at a dose 300 kGy. A gradual increase in the dose of γ-irradiation above 300 kGy is accompanied by a rise in the laser ablation rate. At γ-irradiation doses up to 2.3 MGy, the rate of the post-irradiated laser ablation of PVDF reaches 6.5 mg/s, which is equal to the laser ablation rate of non-irradiated PVDF.

The pseudo-network structure of the amorphous block of polytetrafluoroethylene is formed by branching points, the crystallites of low- and high-melting crystalline polymorphs and the cluster segments of macromolecules. The polymer treated by laser irradiation is amorphized, with the degree of amorphization and other changes depending on the radiation fluence. A depression of the molecular flow onset and initial melting temperatures of the crystalline polymorphs, a decrease in the molecular mass, and the disappearance of the crystalline branching points characteristic of the original polymer have been observed in the irradiated polymer. Areas with different degrees of modification of the molecular structure appear in the dynamic mode with moving boundaries during continuous CO 2 laser irradiation. The difference in absorbance of the crystalline and amorphous portions of the polymer at the laser emission wavelength and a relatively high transmittance make laser-induced degradation differ from thermolysis in contact with a hot surface.

Results of a pioneering study of the effect of laser radiation in vacuum on the surface of a polyketone (alternating terpolymer of ethylene, propylene, and carbon monoxide, POK) plate are presented. It has been found that laser beam irradiation leads to the surface heating of the plate, its melting, and the formation of a characteristic surface microrelief, an ablation crater, from which the gas flow of the ablation plume carries away products that are deposited on surfaces outside the laser beam area to form a coating with a chemical composition close to that of the substrate POK. A rim grows from molten POK around the crater. The melting point of the crystalline modification (377 K), the molecular flow temperature (427 K), and the molecular weight of the coating (25560) are much lower than those of the initial POK (464 K, 477 K, and 159200, respectively), thereby indicating laser-induced chain degradation of POK. The preliminary γ-irradiation of POK to a dose of 100 kGy enhances its laser ablation rate.

The impact of high-intensity laser radiation on a polymer in vacuum is accompanied by the release of gaseous products of degradation and, in some cases, of clusters of the partially destroyed polymer. Polytetrafluoroethylene (PTFE) exhibits an abnormal behavior in this process: being exposed to continuous CO2 laser radiation, it degrades at a high rate and its clusters have a fibrous form. Depending on the irradiation conditions, the fibrous fraction forms two types of product, “cotton wool” and “felt”. Polytetrafluoroethylene and its laser-modified “cotton wool“ product have a semicrystalline topological structure. The preliminary γ-irradiation of PTFE enhances the laser ablation process.

Anomalous behavior of polytetrafluoroethylene (PTFE) under the action of CO2 laser radiation in vacuum is discussed. A feature of the ablation process is formation of polymer fibers which quantity depends on the target preliminary treatment and the ablation conditions. Experimental results are set out and possible mechanisms of the polymer fibering are discussed. A conclusion is made concerning two dynamic polymer components differ by the resistance to the laser beam action, appearing in the ablation crater. A method is proposed for producing unique fiber-porous polytetrafluoroethylene materials and other useful products as well as for the polytetrafluoroethylene wastes recycling. The results of industrial application of these new fiberporous materials are discussed.