The hydrolytic and enzymatic degradation of polymer films of poly(3-hydroxybutyrate) (PHB) of different molecular mass and its copolymers with 3-hydroxyvalerate (PHBV) of different 3-hydroxyvalerate (3-HV) content and molecular mass, 3-hydroxy-4-methylvalerate (PHB4MV), and polyethylene glycol (PHBV-PEG) produced by the Azotobacter chroococcum 7B by controlled biosynthesis technique were studied under in vitro model conditions. The changes in the physicochemical properties of the polymers during their in vitro degradation in the pancreatic lipase solution and in phosphate-buffered saline for a long time (183 days) were investigated using different analytical techniques. A mathematical model was used to analyze the kinetics of hydrolytic degradation of poly(3-hydroxyaklannoate)s by not autocatalytic and autocatalytic hydrolysis mechanisms. It was also shown that the degree of crystallinity of some polymers changes differently during degradation in vitro. The total mass of the films decreased slightly up to 8–9% (for the high-molecular weight PHBV with the 3-HV content 17.6% and 9%), in contrast to the copolymer molecular mass, the decrease of which reached 80%. The contact angle for all copolymers after the enzymatic degradation decreased by an average value of 23% compared to 17% after the hydrolytic degradation. Young’s modulus increased up to 2-fold. It was shown that the effect of autocatalysis was observed during enzymatic degradation, while autocatalysis was not available during hydrolytic degradation. During hydrolytic and enzymatic degradation in vitro, it was found that PHBV, containing 5.7–5.9 mol.% 3-HV and having about 50% crystallinity degree, presents critical content, beyond which the structural and mechanical properties of the copolymer have essentially changed. The obtained results could be applicable to biomedical polymer systems and food packaging materials.

To a considerable degree hardness is an empirical value which depends on many details involved in the measuring process. In the present work, hardness values were measured in the depth range 2 – 800 nm using microhardness, nanoindentation and scratch hardness tests on fused silica, steel and sapphire. It is shown that overestimation of hardness values for steel and sapphire with the nanoindentation method can be directly related to the relative height of pile-ups observed on the topography image of the indentation imprint. It is also shown that the scratch hardness test is a promising technique for nanoscaled hardness measurements.

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A comparative study of wear resistance, hardness and elastic modulus in samples of VT6 titanium alloy with a mineral coating created using low-temperature technological operations (local heating up to 80°C) and without coating was performed. The hardness and elastic modulus in nanoindentation mode were measured by applying a series of indentations with various maximum loads. The load was selected in a way that penetration depth of the tip into the material ranged from 500 nm to 4 μm with an estimated thickness of the modified layer of about 10 μm. The creation of a mineral layer increased the hardness of the surface of the titanium alloy sample by 45 -70 % and also caused a 2 -3 times increase of the roughness parameters of samples. Taking into account the specific features of measuring physical and mechanical properties of thin modified layers, wear resistance was measured using the method of multi-cycle friction with a sapphire sphere, while controlling the clamping force and deepness of the tip penetration into the sample. Wear resistance of the surface of the sample modified by minerals increased by 4 -5 times as compared to the wear resistance of the surface of the VT6 titanium alloy without a modification. By authors' opinion, the results of the studies reveal big potentials of using metal parts from titanium and titanium alloys with mineral coatings in various devices and mechanical assemblies. Проведено сравнительное исследование износостойкости, твердости и модуля упругости образцов из титаново-го сплава ВТ6 с минеральным покрытием, созданным при использовании низкотемпературных технологических операций (с локальным нагревом до 80°С), и без покрытия. Измерения твердости и модуля упругости в режиме наноиндентирования были проведены путем нанесения серии уколов с различной максимальной нагрузкой. Нагруз-ка подбиралась таким образом, чтобы глубина внедрения наконечника в материал составляла от 500 нм до 4 мкм при оценочной толщине модифицированного слоя около 10 мкм. Создание минерального слоя увеличило твердость поверхности образца из титанового сплава на 45 -70 %, а также увеличило параметры шероховатости образцов в 2 -3 раза. Корректность измерения определяется тем, что на малых глубинах влияние подложки на измеряемые величины мала, и поэтому ею можно было пренебречь. Разброс данных сопоставим с измеряемыми величинами, что, возможно, связано с относительно большой шероховатостью образцов. Учитывая особенности измерения фи-зико-механических свойств тонких модифицированных слоев, измерение износостойкости было выполнено мето-дом многоциклового трения сапфировой сферой с контролем силы прижима и углубления наконечника в образец. Использование такой системы измерения особенно важно при испытании тонких слоев, когда толщина слоя со-поставима с параметрами шероховатости поверхности. Износостойкость поверхности образца, модифицирован-ной минералами, увеличилась в 4 -5 раз по сравнению с износостойкостью поверхности титанового сплава ВТ6 без модификации. По мнению авторов, результаты исследования открывают бол...

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