Anda Dzene

Improvement of the deformative characteristics of poly-β-hydroxybutyrate by plasticization

Plasticized systems of poly-β-hydroxybutyrate (PHB) are studied, where low-molecular compounds traditionally used for this purpose for various systems, i.e., dioctyl sebacate, dibutyl sebacate, polyethylene glycol, Laprol 503, and Laprol 5003, are used as plasticizers. All of them are nontoxic and biodegradable compounds with a similar molecular weight and comparable polarity of molecules. The main purpose of this study is to improve the deformability of PHB taking into account the structural changes in plasticized PHBs. The plasticizers chosen are completely compatible with the polymer and form a monophase system up to a plasticizer content of 15–20%. An increase in the plasticizer content allows us to increase efficiently the deformability of the polymer (the relative breaking elongation of PHB at room temperature grows up to 250–300%). At the same time, the system becomes considerably weaker and therefore there is no point in increasing the concentration of plasticizers by more than 20 wt.%. According to the data obtained from DSC measurements, the ratio between the amorphous and crystalline regions of PHB in the presence of plasticizers mentioned remains practically constant. The changes in the elastic properties of PHB/low-molecular plasticizer systems are mainly due to efficient weakening of intermolecular interactions in the amorphous regions of the polymer. A slight decrease in the crystalline order of PHB is of secondary importance.

Biodegradable materials from plasticized PHB biomass

Biodegradation rate in different environments as well as deformation characteristics of poly-β-hydroxybutyrate (PHB), PHB biomass and of plasticized systems thereof have been investigated. Polyethylene glycol (PEG) and oxypropylated glycerine or laprol (LAP) were selected as plasticizers. Increase of the content of plasticizer from 5 to 50 % gave rise of the elongation at break from 4 to 25 % for LAP and from 2 to 9 % for PEG, respectively. No significant changes of strength were recorded. It remained comparatively small - around 2.5 MPa. PHB, biomass and the PHB composition containing 10 % PEG completely decomposed in soil during 30 days. PHB containing 33 % of biologically stable LAP additives lost half of its mass at the same period. Structural changes of plasticized biomass are also shown.

Characterization of various kinds of paper as reinforcement for biodegradable polymer composites

Some structural characteristics and properties of a diverse paper selection were studied with the aim to create biodegradable polymer composites for packaging materials. Paper in such composites would serve as a reinforcement and biodegradable polymer as a matrix. Tensile and tear properties of the tested papers depended not only on paper density (or void content) but also on some other paper structure features. As polymers for composite production are applied from solution, the impact of solvent on the mechanical properties of paper was investigated.

Synthesis and properties of hydrophilic segmented poly(urethanes) based on poly(ethylene glycols) and glycerol monostearate

Poly(urethanes) having the structure of comb-shaped copolymers were synthesized from glycerol monostearate, poly(ethylene glycols) with M n = 300–6000, and 1,6-hexamethylene diisocyanate. Effects of the molecular mass of segments and of the contents of soft segments and side chains on both the glass transition temperature of the soft segment and on the melting point and the enthalpy of melting of crystalline phases involving soft segments and side chains were studied by DSC and IR spectroscopy. The resulting comb-shaped copolymers were shown to exhibit thermoplastic and hydrophilic behavior. It was demonstrated that the ultimate tensile strength, yield stress, and Young’s modulus of copolymer films increase with an increase in the molecular masses of soft and hard segments with their ratio maintained constant.

Development of Poly(vinyl alcohol) Based Systems for Wound Dressings

Poly(vinyl alcohol) hydrogels are of special interest for the application in medicine (mainly for therapeutic systems) due to their biocompatibility and excellent ability to absorb water. The water absorption of different gels prepared by freezing/thawing method was studied in the presented work.

Biodegradable Flax Fiber Reinforced Eco-Composites

Formation process of flax fiber reinforced biocomposites based on waterborne matrix systems from modified polymers - polyhydroxybutyrate, poly (vinyl alcohol) was developed by suspension casting technique. Two kind of flax fiber as reinforcement was employed Latvian variety Vega-2 and flax combing. The correlation between matrix composition, fiber origin, content and mechanical characteristics, water vapour absorption and biodegradability was established. Optimal characteristics of elaborated eco-composites were obtained by use of flax combing with fiber content ~ 30 wt. %.

PHA Latex Composite Films: Mechanical Properties and Surface Visualization

Homopolymer PHB and copolymer PHB/HV containing granules were isolated from Azotobacter chroococcum cells and used for latexes formation. Composite latex films were formed from the PHB and PHB/HV latexes with different content of poly (vinyl alcohol) and glycerol and a hydrophobic fluorescent benzanthrone derivated dye 3-piperidinobenzanthrone, possessed high fluorescence intensity in a system with PHA granules. Fluorescence based methods were used for characterization of the elaborated latex film by their stability at high temperature and for visualization of the film surfaces PHA granules distribution. Film stability in phosphate buffered saline was evaluated by dye migration activity in the solution. The results of mechanical testing of the latex films were compared with the stability testing and surface visualization results. The data obtained allow a better understanding the difference of the mechanical and physical properties of the investigated films.

Synthesis and properties of poly(ester urethanes) based on cellulose triacetate

Segmented poly(ester urethanes) were synthesized from oligomeric cellulose triacetate diols, poly(caprolactone)diols, and 1,6-hexamethylene diisocyanate. The effects of the molecular mass and structure of soft and hard segments of poly(ester urethanes) on their thermal behavior, mechanical properties, and degradation in aqueous solutions of a phosphate buffer were studied by DSC and IR spectroscopy. The combination of soft segments derived from poly(caprolactone)diols with M = (1.0–3.5) × 103, hard segments based on depolymerized cellulose triacetate with M = (2–4) × 103, and 1,6-hexamethylene diisocyanate makes it possible to synthesize poly(ester urethanes) with excellent mechanical characteristics. The degree of crystallinity of these polymers increases with a decrease in the molecular mass of the depolymerized cellulose triacetate block in the hard segment. As the soft segment lengthens, phase separation between domains of soft and hard segments becomes more pronounced. Upon incorporation of poly(ethylene glycol) blocks into the soft segments of poly(ester urethanes), their hydrophobicity is enhanced and biodegradability is accelerated.

Characteristics of Biodegradable Poly(Ester-Urethanes) with Side Chains

Two series of segmented poly(ester-urethanes) (SPEU) have been studied. The flexible segment of SPEU was formed from polycaprolactonediols (PCL diols) with a molecular mass of 600 to 10000 and the rigid one — from a blend of 2.4 and 2.6-toluene diisocyanates (TDI) and a chain extender. The first series of SPEU contained no side branches, whereas in the second series, side branches in the form of long chains of aliphatic structure were present at the rigid segment. The tensile strength of SPEU decreased when the molecular mass of the flexible segment increased from 600 to 2000; in this case, the specimens were of amorphous structure. An increase in the molecular mass of the flexible segment from 2000 to 10000 led to an increase in its degree of crystallinity and in the melting point, fusion enthalpy, tensile strength, yield stress in tension, and packing coefficient of SPEU. The side chains at the rigid segment affected the degree of phase separation insignificantly, but decreased the order of the structure, the glass transition temperature, and strength properties of SPEU, whereas the side chains at the flexible segment reduced its crystallinity.