Mari Pauliina Hiljanen-Vainio

Biodegradable lactone copolymers. I. Characterization and mechanical behavior of ε‐caprolactone and lactide copolymers

Copolymers of e-caprolactone and L-lactide (e-CL/L-LA) and e-caprolactone and DL-lactide (e-CL/DL-LA) were synthesized with compositions 80/20, 60/40, and 40/60 (wt % in feed). The polymerization temperature was 140°C and Sn(II)octoate was used as a catalyst. The effect of the comonomer ratio on the thermal and mechanical properties of the copolymers was investigated by size-exclusion chromatography (SEC), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectrometry, and tensile testing. The copolymers differed widely in their physical characteristics, ranging from weak elastomers to tougher thermoplastics according to the ratio of e-CL and LA in the copolymerization. Poly(L-lactide) (PLLA), poly(DL-lactide) (PDLLA), and poly(e-caprolactone) (PCL) homopolymers were studied as references. The tensile modulus and tensile strength were much higher for PLLA, PDLLA, and PCL homopolymers than for the copolymers. The maximum strain was very low for PLLA and PDLLA, whereas the copolymers and PCL exhibited large elongation.

Biodegradable lactone copolymers. II. Hydrolytic study of ε-caprolactone and lactide copolymers

Copolymers of e-CL/L-LA and e-CL/DL-LA were allowed to age in a buffer solution of pH 7 at 23 and 37°C. The effects of time and temperature on the rate of hydrolysis were examined by various techniques including weighing (water absorption and weight loss), SEC (molecular weight and polydispersity), and DSC (thermal properties). For comparison, the hydrolytic behavior of PLLA, PDLLA, and commercial PCL homopolymers was investigated by the same methods. SEC measurements showed that molecular weights of the copolymers and PLA homopolymers started to decrease during the first week of hydrolysis, but significant mass losses occurred only much later. As expected, there was no change in either molecular weight or mass of PCL during the hydrolysis study. The kinetic results for copolymers and homopolymers were calculated to study the degradation mechanism. During hydrolysis, the crystallinity of the initially semicrystalline copolymers increased and some crystallinity appeared in the initially amorphous L-LA-containing copolymers.

Properties of ε-caprolactone/DL-lactide (ε-Cl/DL-LA) copolymers with a minor ε-Cl content

In this study the properties of DL-lactide (DL-LA) copolymers with 5, 10, 15, 20, and 30 wt % (in feed) of epsilon-caprolactone (epsilon-CL) polymerized with stannous(II)octoate (SnOct) as catalyst and glycerol, laurylalcohol, or pentaerythritol as initiator were investigated. Thermal studies showed that the addition of 5 wt % (in feed) of epsilon-CL to the P(CL/DL-LA) copolymer decreased the Tg by about 5 degrees C. Hydrolysis tests were carried out for copolymers with 20 and 30 wt % (in feed) of epsilon-CL to study the degradation rate. Molecular weights decreased dramatically during the first week of hydrolysis, with mass losses occuring a few weeks later. The influence of glycerol and pentaerythritol as initiators, and the influence of epsilon-CL content on stress-strain behavior, tension set, and rheologic properties of the P(CL/DL-LA) copolymers were also investigated. The tensile testing of P(CL/DL-LA) copolymers containing 5, 10, 15, 20 wt % (in feed) of epsilon-CL showed that the properties of copolymers varied from hard and brittle to rubbery. The permanence of elastic properties was investigated with tension set measurements. These studies showed that copolymers crept remarkably under stress. The viscosity and elasticity of P(CL/DL-LA) copolymers at 120 degrees C were investigated using rheology studies.

Biodegradable lactone copolymers. III. Mechanical properties of ε-caprolactone and lactide copolymers after hydrolysis in vitro

Copolymers of e-CL/L-LA and e-CL/DL-LA and for comparison homopolymers PLLA, PDLLA, and PCL were allowed to age in a buffer solution of pH 7 at 23 and 37°C and studied for the changes in the mechanical properties taking place as a function of hydrolysis time. Tensile modulus measurements showed the copolymers to retain their modulus much longer than did the PLA homopolymers. The copolymers became stiffer with hydrolysis, while the elongation at break decreased gradually. For the amorphous P(CL60/L-LA40) copolymer, the tensile modulus and yield stress values increased dramatically in hydrolysis. The initial copolymer was soft and tough but became more brittle during hydrolysis, and it exhibited a plasticlike rather than a rubberlike deformation, though the stress values were still very low. After a short period of decrease at the beginning of hydrolysis, the tensile modulus of P(CL80/L-LA20) and P(CL40/L-LA60) copolymers to some extent increased. Yield stress values for these copolymers decreased during hydrolysis. The tensile modulus of PLLA and PDLLA began to decrease during the first days, i.e., the material became weaker. In the case of PCL, the tensile modulus remained almost the same during the 70 days of the test. The degradation was also studied by 13C-NMR. Caproyl homopolymeric sequences did not degrade significantly during hydrolysis.

Reinforcement of biodegradable poly(ester-urethane) with fillers

Abstract Two novel poly(ester-urethanes) (PEUs: PEUa and PEUb) were reinforced by blending in a batch mixer with organic and inorganic fillers of different particle sizes and shapes. In most experiments the filler contents were 0, 5, 15, 30, and 50 wt.%. In general, both the particulate and fibre-like fillers increased the stiffness almost linearly with increasing filler content, but the tensile and impact strengths and strain at break showed a downward trend. Exceptionally, improvements in tensile strength were achieved with glass fibre, as expected, and, surprisingly, also with some blend compositions containing silicate-type fillers. In addition, slightly improved impact strength was achieved with a small amount of fine talc. Dynamic-mechanical thermal analysis confirmed the reinforcing effects and showed some slight changes in the glass transition temperature of the PEU. Scanning electron microscopy studies on the morphology revealed relatively good mixing and contact between all the fillers and PEU.

Impact modification of lactic acid based poly(ester‐urethanes) by blending

Branched biodegradable poly(ester-urethane)(PEU) was blended with two elastic biodegradable copolymers in proportions 5, 10, 15, and 20 wt % to investigate their effect on this hard and brittle polymer. Copolymer of L-lactide and ϵ-caprolactone, P(L-LA50/CL50), was synthesized by ring-opening polymerization and the other elastic poly(L-lactic acid-co-ϵ-caprolactone)urethane, P(LA50/CL50)U, was prepared by direct polycondensation of L-lactic acid and ϵ-caprolactone, followed with urethane bonding. In addition, four elastic biodegradable copolymers, three of them P(L-LA/CL) and one P(LA/CL)U, were blended with linear PEU to investigate their modifying effect on PEU. These compositions studied were 10, 15, and 20 wt % of P(L-LA40/CL60), P(L-LA60/CL40), P(L-LA80/CL20), and P(LA40/CL60)U in PEU. Blending was done in a batch mixer. PEU became more ductile when blended with P(L-LA/CL) and P(LA/CL)U, and its impact resistance improved markedly. In general, an addition of 15 wt % of copolymer appeared to give the most desirable mechanical properties. Moreover, the more L-lactide in the P(L-LA/CL) copolymer, the better was the miscibility of the blends, as shown by dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). One P(L-LA/CL) was also blended with poly(DL-lactide) (PDLLA) to see if the dispersion of rubbery copolymer particles was the same in PDLLA and PEU. A well-known commercial nonbiodegradable rubber [styrene/ethylene/butylene copolymer (SEBS)] was blended with linear PEU to compare its effect on impact strength.

Miscibility, Morphology and Mechanical Properties of Rubber-Modified Biodegradable Poly(ester-urethanes)

Biodegradable, lactic acid based amorphous poly(ester-urethane)s (PEU) were modified with poly(L-lactic acid-co-e-caprolactone-urethane) elastomer (P[LA/ CL]U) by melt blending. The phase separation of P(LA/CL)U elastomer with three different e-caprolactone (CL) compositions (CL content 30, 50, and 70 mol %) and the mechanical properties of the resulting impact-modified linear and branched PEU were investigated. The amounts of P(LA/CL)U elastomer in the PEU blends were 10, 15, 20, and 30 wt %. Dynamic mechanical thermal analysis (DMTA) of the blends with P(LA50/CL50)U and P(LA30/CL70)U elastomers revealed separate glass transition temperatures for rubber and matrix, indicating phase separation. No phase separation was found for P(LA70/CL30)U elastomer. The effect of mixing rate and temperature during processing on composite properties was tested by blending P(LA30/CL70)U rubber with PEU under various processing conditions. Impact modification studies were also made with two P(LA30/CL70)U elastomers having different amounts of functional groups. The influence of end-functionalization and cross-linking on mechanical properties was investigated in blends containing PEU and 15 wt % of these elastomers. Scanning electron microscopy (SEM) showed the morphology to change dramatically with increase in the degree of cross-linking in the rubber.