Synthesis and structure control of l‐lactic acid–glycolic acid copolymer by homo‐copolymerization

A two‐step direct melt copolymerization process of l ‐lactic acid (L ‐LA)/glycolic acid (GA) was developed: poly(l ‐lactic acid) (PLLA) and poly(glycolic acid) (PGA) with different molecular weight was first synthesized respectively by binary catalyst (tin chloride/p‐toluenesulfonic or tin chloride); and then poly(l ‐lactic‐co‐glycolic acid) (b‐PLGA) was produced by melt polymerization of the as‐prepared PLLA and PGA, wherein the composition and chain structure of b‐PLGA copolymers could be controlled by the molecular weight of PLLA. The chain structure and thermal properties of copolymers were studied by Wide‐angle X‐ray diffraction, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. In comparison with the random PLGA (r‐PLGA) synthesized by one‐step direct melt polymerization, the average l ‐lactic blocks length (L_LA) in b‐PLGA was longer while the average glycolic blocks length (L_GA) in b‐PLGA was shorter which further resulted in the improved crystallinity and thermostability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41566.     

Thermal properties and miscibility of semi‐crystalline and amorphous PLA blends

The focus of this research is the study of the microstructures and miscibility at the interface between semi‐crystalline and amorphous PLAs [poly (l ‐lactic acid)(PLLA) with poly (l ,d ‐lactic acid)(PDLLA), respectively]. The blends are prepared through thermal processing (extrusion and hot‐pressing). To increase the area of interface between PDLLA and PLLA, the fibers from PLLA and PDLLA are used. Thermal and microstructures of the blends were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), dynamic thermogravimetric analysis(DMA), small‐angle X‐ray diffraction(SAXS) and wide‐angle X‐ray diffraction (WAXD). The two PLAs are miscible in molten state. However, phase separation is detected after various thermal treatments, with PDLLA being excluded from the regions of interlamellar PLLA regions when PDLLA content is low, as determined from X‐ray diffraction studies. The compatibility between the two PLAs is not perfect in the molten state, since enthalpies of the various blends at T_g are lower than any pure PLA material. The semi‐crystalline PLLA fiber can recrystallize alone in the molten amorphous PDLLA, and a higher nuclei density is observed at the interface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41205.     

Stretch‐induced molecular ordering in amorphous/crystalline polylactide blends

The effect of amorphous poly(D ,L ‐lactide) (PDLLA) on the molecular orientation and crystallization of crystalline poly(L ‐lactide) (PLLA) on stretching is reported in this study. It is indicated that the presence of PDLLA in its miscible blends with PLLA is not favorable for either cohesive mesophase formation below T_g or strain‐induced crystallization above T_g at strains beyond the segmental extensibility limit. Because of lack of constraints imposed by cohesive mesophase or crystals, oriented segments are liable to slide each other or recoil, responsible for low‐molecular orientation in the stretched blends. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L‐lactide) blend

Reaction after mixing of liquid epoxidized natural rubber/poly(L ‐lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L ‐lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (T_g) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while T_g and melting temperature (T_m) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high‐resolution solid‐state ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Reactive blending of poly(L‐lactic acid) with poly(ethylene‐co‐vinyl alcohol)

Poly(L ‐lactic acid) (PLLA) was blended with poly(ethylene‐co‐vinyl alcohol) (EVOH) in the presence of an esterification catalyst to induce reaction between the hydroxyl groups of EVOH and the terminal carboxylic group of PLLA. Nascent low‐molecular‐weight PLLA, obtained from a direct condensation polymerization of L ‐lactic acid in bulk state, was used for the blending. Domain size of the PLLA phase in the graft copolymer was much smaller than that corresponding to a PLLA/EVOH simple blend. The mechanical properties of the graft copolymer were far superior to those of the simple blend, and the graft copolymer exhibited excellent mechanical properties even though the biodegradable fraction substantially exceeded the percolation level. The grafted PLLA reduced the crystallization rate of the EVOH moiety. Melting peak temperature (T_m) of the PLLA phase was not observed until the content of PLLA in the graft reaction medium went over 60 wt %. The modified Sturm test results demonstrated that biodegradation of EVOH‐g‐PLLA took place more slowly than that of an EVOH/PLLA simple blend, indicating that the chemically bound PLLA moiety was less susceptible to microbial attack than PLLA in the simple blend. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 886–890, 2005     

Synthesis of poly(D,L‐lactic acid) modified by triethanolamine by direct melt copolycondensation and its characterization

Using D ,L ‐lactic acid (LA) and multifunctional group compound triethanolamine (TEA) as starting materials, a novel biodegradable material poly(D ,L ‐lactic acid‐triethanolamine) [P(LA‐TEA)] was directly synthesized by simpler and practical melt polycondensation. The appropriate synthetic condition was discussed in detail. When the molar feed ratio LA/TEA was 30/1, the optimal synthesis conditions were as follows: a prepolymerization time of 12 h; 0.5 weight percent (wt %) SnO catalyst; and melt copolycondensation for 8 h at 160°C, which gave a novel star‐shaped poly(D,L ‐lactic acid) (PDLLA) modified by TEA with the maximum intrinsic viscosity [η] 0.93 dL g⁻¹. The copolymer P(LA‐TEA) as a different molar feed ratio was characterized by [η], Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H‐NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). Increasing the molar feed ratio of LA/TEA, T_g and M_w increased. However, all copolymers were amorphous, and their T_g (12.2°C–32.5°C) were lower than that of homopolymer PDLLA. The biggest M_w was 9400 Da, which made the biodegradable polymer be potentially used as drug delivery carrier, tissue engineering material, and green finishing agent in textile industry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Enhanced crystallization rate and mechanical properties of poly(l‐lactic acid) by stereocomplexation with four‐armed poly(ϵ‐caprolactone)‐block‐poly(d‐lactic acid) diblock copolymer

Poly(l ‐lactic acid) (PLLA) was blended with a series of four‐armed poly(? ‐caprolactone)‐block ‐poly(d ‐lactic acid) (4a‐PCL‐b ‐PDLA) copolymers in order to improve its crystallization rate and mechanical properties. It is found that a higher content of 4a‐PCL‐b ‐PDLA copolymer or longer PDLA block in the copolymer lead to faster crystallization of the blend, which is attributed to the formation of stereocomplex crystallites between PLLA matrix and PDLA blocks of the 4a‐PCL‐b ‐PDLA copolymers. Meanwhile, the PDLA block can improve the miscibility between flexible PCL phase and PLLA phase, which is beneficial for improving mechanical properties. The tensile results indicate that the 10% 4a‐PCL_5k‐b ‐PDLA_5k/PLLA blend has the largest elongation at break of about 72% because of the synergistic effects of stereocomplexation between enantiomeric PLAs, multi‐arm structure and plasticization of PCL blocks. It is concluded that well‐controlled composition and content of 4a‐PCL‐b ‐PDLA copolymer in PLLA blends can significantly improve the crystallization rate and mechanical properties of the PLLA matrix. © 2017 Society of Chemical Industry     

Direct synthesis of poly(D,L‐lactic acid) by melt polycondensation and its application in drug delivery

Starting from D,L ‐acid and SnCl₂ as catalyst, poly(D,L ‐lactic acid) (PDLLA) was directly synthesized by melt polycondensation. Under the appropriate conditions such as 0.5 wt % SnCl₂, 170–180°C, 70 Pa, and 10 h, the viscosity‐average molecular weight (M_η) of PDLLA was 4100 Da. PDLLA produced by the most practical method was used as the drug‐delivery material for erythromycin and ciprofloxacin. The optimal conditions for the preparation of erythromycin–poly(D,L ‐lactic acid)–microsphere (ERY–PDLLA–MS) for lung targeting was investigated, and further confirmed by good reappearance tests. DSC and SEM demonstrated that ERY–PDLLA–MS had good spherical shape. The release in vitro of ERY–PDLLA–MS was effective and the half‐time (T_1/2) was 51.0 h. After 175 h, the accumulated release percentage was 80.0%. The test in vivo showed that ERY–PDLLA–MS was more easily distributed in rabbit lung tissue. When PDLLA was applied in an antibacterial ciprofloxacin drug‐delivery microsphere (CIP–PDLLA–MS), CIP–PDLLA–MS was also characterized with DSC and SEM, and the release T_1/2 in vitro was 24.9 h. After 53.2 h, the accumulated release percentage reached 84.0%, which indicated that CIP–PDLLA–MS was advantageous to long‐term release. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2143–2150, 2004     

Part 7. Effects of poly(L‐lactide‐co‐ϵ‐caprolactone) on morphology,structure, crystallization,and physical properties of blends of poly(L‐lactide) and poly(ϵ‐caprolactone)

Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (T_m) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X_PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the X_PLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at X_PLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the X_PLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry     

Poly(para‐dioxanone)/poly(D,L‐lactide) blends compatibilized with poly(D,L‐lactide‐co‐para‐dioxanone)

The effect of poly(D ,L ‐lactide‐co‐para‐dioxanone) (PLADO) as the compatibilizer on the properties of the blend of poly(para‐dioxanone) (PPDO) and poly(D ,L ‐lactide) (PDLLA) has been investigated. The 80/20 PPDO/PDLLA blends containing from 1% to 10% of random copolymer PLADO were prepared by solution coprecipitation. The PLADO component played a very important role in determining morphology, thermal, mechanical, and hydrophilic properties of the blends. Addition of PLADO into the blends could enhance the compatibility between dispersed PDLLA phase and PPDO matrix; the boundary between the two phases became unclear and even the smallest holes were not detected. On the other hand, the position of the T_g was composition dependent; when 5% PLADO was added into blend, the T_g distance between PPDO and PDLLA was shortened. The blends with various contents of compatibilizer had better mechanical properties compared with simple PPDO/PDLLA binary polymer blend, and such characteristics further improved as adding 5% random copolymers. The maximum observed tensile strength was 29.05 MPa for the compatibilized PPDO/PDLLA blend with 5% PLADO, whereas tensile strength of the uncompatibilized PPDO/PDLLA blend was 14.03 MPa, which was the lowest tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of stereoisomerism of poly(lactic acid) during neural guide conduit membrane synthesis

Poly(lactic acid) membranes are being developed as biomaterials for several purposes such as artificial implants for peripheral nerve injury, also known as neural guide conduits (NGC). These membranes need to meet standards of mechanical, degradability, and permeability properties, besides dimensional and structural requirements. Among the stereoisomers of polylactides, poly(l ‐lactic acid), and poly(d ,l ‐lactic acid) are the most used as biomaterials, having significant differences in solubility, crystallinity thermal, and mechanical properties. In this work, PLLA and PDLLA were compared for hollow fiber membrane synthesis by liquid induced phase separation. PLLA samples presented 18% of crystallinity, while PDLLA is amorphous. PDLLA and PLLA polymer solutions on N‐methyl‐pyrrolidone presented values of 3428 and 320.2 cP, respectively. In immersion of PLA‐NMP solutions in water, PLLA solution presented instantaneous demixing, while PDLLA showed a 28 s delay on precipitation. The PLLA–NMP–water has a larger demixing region compared to PDLLA–NMP–water system. Hollow fibers of both polymers presented closed external surface with finger‐like macropores morphology in their cross‐sections. PDLLA presented typical liquid–liquid demixing pores while PLLA presented spherulitical crystalline solid–liquid separation structures, which deeply compromised its mechanical properties. PDLLA presented as a good candidate for hollow fiber NGC material, as presented good mechanical resistance in tensile and suture simulating tests. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46190.     

Synthesis,physical properties,and crystallization of optically active poly(L‐phenyllactic acid) and poly(L‐phenyllactic acid‐co‐L‐lactic acid)

Optically active poly(L ‐phenyllactic acid) (Ph‐PLLA), poly(L ‐lactic acid) (PLLA), and poly(L ‐phenyllactic acid‐co‐L ‐lactic acid) with weight‐average molecular weight exceeding 6 × 10³ g mol^?1 were successfully synthesized by acid catalyzed direct polycondensation of L ‐phenyllactic acid and/or L ‐lactic acid in the presence of 2.5–10 wt % of p‐toluenesulfonic acid. Their physical properties and crystallization behavior were investigated by differential scanning calorimetry, thermogravimetry, and polarimetry. The absolute value of specific optical rotation ([α]) for Ph‐PLLA (?38 deg dm^?1 g^?1 cm³) was much lower than that of [α] for PLLA (?150 deg dm^?1 g^?1 cm³), suggesting that the helical nature was reduced by incorporation of bulky phenyl group. PLLA was crystallizable during solvent evaporation, heating from room temperature, and cooling from the melt. Incorporation of a very low content of bulky phenyllactyl units even at 4 mol % suppressed the crystallization of L ‐lactyl unit sequences during heating and cooling, though the copolymers were crystallizable for L ‐phenylactyl units up to 6 mol % during solvent evaporation. The activation energy of thermal degradation (ΔE_td) for Ph‐PLLA (200 kJ mol^?1) was higher than that for PLLA (158 kJ mol^?1). The ΔE_td for the copolymers increased with an increase in L ‐phenyllactyl unit content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Formation of co‐continuous PLLA/PC blends with significantly improved physical properties by reactive comb polymers

A kind of reactive comb (RC) polymer, which is constituted by poly(methyl methacrylate) backbone and side chains and a few epoxide groups that distribute randomly along the backbone, has been applied as compatibilizers for the thermodynamically immiscible poly(l ‐lactide) (PLLA)/polycarbonate (PC) blend (50/50, wt/wt). Phase morphology and physical properties of the compatibilized PLLA/PC blends are characterized by scanning electron microscopy, transmission electron microscopy, and tensile tests. It has been found that the morphologies of the PLLA/PC blends are significantly ameliorated with the addition of RC polymers. A type of PLLA/PC blend with stable co‐continuous morphology has been achieved by the incorporation of more than 3 wt % of RC polymers. The mechanical tests showed that the co‐continuous PLLA/PC blends have an excellent stiffness‐toughness balance with high modulus and significantly improved ductility. Especially, the elongation at break of the PLLA/PC blend compatibilized by 10 wt % of RC polymers is 10 times higher than that of neat PLLA, in which the blend exhibits a cocontinuous lamellar microstructure. Furthermore, the PLLA/PC blends with cocontinuous morphology exhibit dramatically improved thermal stability as compared to neat PLLA when the temperature is over the T_g of the PLLA phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46047.     

Compatibility of poly(butadiene‐co‐acrylonitrile) with poly(L‐lactide) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)

Poly(L ‐lactide) (PLLA) and poly(3‐hydrobutyrate‐co‐3‐hydroxyvalerate) (PHBV) were blended with poly(butadiene‐co‐acrylonitrile) (NBR). Both PLLA/NBR and PHBV/NBR blends exhibited higher tensile properties as the content of acrylonitrile unit (AN) of NBR increased from 22 to 50 wt %. However, two separate glass transition temperatures (T_g) appeared in PLLA/NBR blends irrespective of the content of NBR, revealing that PLLA was incompatible with NBR. In contrast, a single T_g, which shifted along with the blend composition, was observed for PHBV/NBR50 blends. Moreover NBR50 suppressed the crystallization of PHBV, indicating that PHBV was compatible with NBR50. Decrease of both elongation modulus and stress at maximum load was less significant and increase of elongation at break was more pronounced in PHBV/NBR50 blends than in PLLA/NBR50 blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3508–3513, 2004     

Properties and Biodegradability of Polymer Blends of Poly(L‐lactide)s with Different Optical Purity of the Lactate Units

Polylactides with high and low L ‐isomeric ratios of the lactate units (PLA99.0 and 77.0, where the numbers correspond to the L ‐ratios) were melt‐blended to analyze the changes in properties and biodegradability with the polymer blend. The crystallinity of the blends was almost similar to that of the blends of PLLA and PDLLA. The glass transition behavior supported the compatibility of both polymers. The glass transition behavior was indicative of a compatible nature of both polymers. The tensile modulus of the blends was almost identical irrespectively of the blend ratio, while their tensile strength decreased with decreasing composition of PLA99.0. Above T_g, the storage modulus of the blends dropped from 2–3×10⁹ Pa to 1–3×10⁶ Pa and then increased to a different level depending on the crystalline nature of the blends. The biodegradability of the blends increased with decreasing composition of PLA99.0. This difference in degradability can be well explained by our random packing model of local helices of the L ‐sequenced chains for the L ‐rich PLA samples.     

Structural changes and biodegradation of PLLA,PCL, and PLGA sponges during in vitro incubation

The structural changes and degradation behaviors of poly(L ‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) sponges were studied by incubation in phosphate buffer solution and compared with those of previously reported poly(lactic‐co‐glycolic acid) (PLGA) sponge. The changes of pH, weight, molecular weight, crystallinity, and thermal properties of glass transition and melting were measured. The influence of incubation temperature on the structural change of each type of sponge was investigated in details. During incubation, the PLLA sponge showed secondary crystallization, the PCL sponge showed lamellar thickening, and the PLGA sponge showed physical aging. Depending on the type of biodegradable polymers, the incubation temperature caused different structural changes during the incubation and the structural changes influenced several degradation behaviors. POLYM. ENG. SCI., 50:1895–1903, 2010. © 2010 Society of Plastics Engineers     

Blends of aliphatic polyesters. VIII. Effects of poly(L‐lactide‐co‐ε‐caprolactone) on enzymatic hydrolysis of poly(L‐lactide), poly(ε‐caprolactone), and their blend films

Poly(L ‐lactide), that is, poly(L ‐lactic acid) (PLLA), poly(ε‐caprolactone) (PCL), and their blend (50/50) films containing different amounts of poly(L ‐lactide‐co‐ε‐caprolactone) (PLLA‐CL), were prepared by solution casting. The effects of added PLLA‐CL on the enzymatic hydrolysis of the films were investigated in the presence of proteinase K and Rhizopus arrhizus lipase by use of gravimetry. The addition of PLLA‐CL decreased the proteinase K–catalyzed hydrolyzabilities of the PLLA and PLLA/PCL (50/50) films as well as the Rhizopus arrhizus lipase‐catalyzed hydrolyzability of the PCL and PLLA/PCL (50/50) films. The decreased enzymatic hydrolyzabilities of the PLLA and PCL films upon addition of PLLA‐CL are attributable to the fact that the PLLA‐CL is miscible with PLLA and PCL and the dissolved PLLA‐CL must disturb the adsorption and/or scission processes of the enzymes. In addition to this effect, the decreased enzymatic hydrolyzabilities of the PLLA/PCL (50/50) films upon addition of PLLA‐CL can be explained by the enhanced compatibility between the PLLA‐rich and PCL‐rich phases arising from the dissolved PLLA‐CL. These effects result in decreased hydrolyzable interfacial area for PLLA/PCL films. The decrement in proteinase K–catalyzed hydrolyzability of the PLLA film upon addition of PLLA‐CL, which is miscible with PLLA, was in marked contrast with the enhanced proteinase K–catalyzed hydrolyzability of the PLLA film upon addition of PCL, which is immiscible with PLLA. This confirms that the miscibility of the second polymer is crucial to determine the proteinase K–catalyzed hydrolyzabilities of the PLLA‐based blend films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 412–419, 2003     

Stereocomplexation and morphology of enantiomeric poly(lactic acid)s with moderate‐molecular‐weight

The thermal behavior and spherulitic morphologies of poly(L ‐lactic acid) (PLLA)/poly(D ‐lactic acid) (PDLA) 1/1 blend with weight‐molecular‐weight of 10⁵ order, together with those of pure PLLA and PDLA, were investigated using differential scanning calorimetry and polarized optical microscopy. It was found that in the blend, stereocomplex crystallites could be formed exclusively or coexisted with homocrystallites depending on thermal history. Banded to nonbanded spherulitic morphological transition occurred for melt‐crystallized PLLA and PDLA, while the blend presented exclusively nonbanded spherulitic morphologies in the temperature range investigated. The spherulite growth of the blend occurred within a wider temperature range (≤180°C) compared with that of homopolymers (≤150°C), while the spherulite growth rates were comparable for both the blend and homopolymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Impact,Thermal, and Morphological Properties of Poly(Lactic Acid)/Poly(Methyl Methacrylate)/Halloysite Nanotube Nanocomposites

Poly(lactic acid)/poly(methyl methacrylate) blends containing halloysite nanotube (2 and 5 phr) and epoxidized natural rubber (5–15 phr) were prepared by melt mixing. The impact strength of poly(lactic acid)/poly(methyl methacrylate) blend was slightly improved by the addition of halloysite nanotube. Adding epoxidized natural rubber further increased the impact strength of poly(lactic acid)/poly(methyl methacrylate)/halloysite nanotube nanocomposite. Single T_g of poly(lactic acid)/poly(methyl methacrylate) is observed and this indicates that poly(lactic acid)/poly(methyl methacrylate) blend is miscible. The addition of halloysite nanotube into poly(lactic acid)/poly(methyl methacrylate) slightly increased the T_g of the blends. The epoxidized natural rubber could encapsulate some of the halloysite nanotube and prevent the halloysite nanotube from breaking into shorter length tube during the melt shearing process.     

Melt‐processed biodegradable polyester blends of poly(L‐lactic acid) and poly(ε‐caprolactone): Effects of processing conditions on biodegradation

Biodegradable polyester blends were prepared from poly(L ‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) (50/50) by melt‐blending, and the effects of processing conditions (shear rate, time, and strain) of melt‐blending on proteinase‐K‐ and lipase‐catalyzed enzymatic degradability were investigated using gravimetry, differential scanning calorimetry, and scanning electron microscopy. The proteinase‐K‐catalyzed degradation rate of the blend films increased and leveled off with increasing the shear rate, time, or strain for melt‐blending, except for the shortest shear time of 60 s. The optimal processing conditions of melt‐blending giving the maximum rate of lipase‐catalyzed degradation were 9.6 × 10² s^?1 and 180 s, whereas a deviation from these conditions caused a reduction in lipase‐catalyzed enzymatic degradation rate. At the highest shear rate of 2.2 × 10³ s^?1, PCL‐rich phase was continuous in the blend films, irrespective of the shear time (or shear strain), whereas PLLA‐rich phase changed from dispersed to continuous by increasing the shear time (or shear strain). This study revealed that the biodegradability of PLLA/PCL blend materials can be manipulated by altering the processing conditions of melt‐blending (shear rate, time, or strain) or the sizes and morphology of PLLA‐rich and PCL‐rich domains. The method reported in the present study can be utilized for controlling the biodegradability of other biodegradable polyester blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 831–841, 2007