Wet Tensile Strength Research Articles

The mechanism of wet-strength development of cellulose sheets prepared with polyamideamine-epichlorohydrin (PAE) resin

The mechanism of wet-strength development of cellulose sheets prepared with typical wet-strength additive, polyamideamine-epichlorohydrin resin (PAE), was studied by some analytical techniques. PAE-containing sheets were prepared from cellulose fibers with different carboxyl contents by either internal addition of PAE to slurries of cellulose fibers or soaking treatment of once-dried cellulose sheets with aqueous PAE solutions. The results showed that carboxyl groups in cellulose fibers behaved as anionic retention sites of cationic PAE molecules for both internal addition of PAE in the sheet-making process and soaking treatment of cellulose sheets with PAE solutions. Moreover, wet-tensile strength of the PAE-containing sheets was clearly improved by heating treatment of the sheets at 110 °C for 10 min, when the cellulose fibers of the sheets clearly had carboxyl groups. FT-IR analysis of PAE films showed that ester bond formation between carboxyl groups at the end of polyamideamine chains in PAE and azetidinium groups of PAE, i.e. within PAE molecules, are possible to occur at least in heated PAE films. PAE-containing cellulose sheets were then subjected to cellulase treatment to obtain PAE-rich fractions in the sheets by removing most of cellulose and hemicellulose fractions without any interactions with PAE. The cellulase-treated residues obtained in the yields of about 1% were analyzed by FT-IR. The result revealed that significant amounts of ester bonds formed between azetidinium groups of PAE and carboxyl groups of cellulose fibers were present in the PAE-containing cellulose sheets, and that these ester bonds increased by heating treatment of the sheets. Thus, it was concluded that wet-strength development of PAE-containing cellulose sheets is primarily ascribed to the ester bond formation between azetidinium groups of PAE and carboxyl groups of cellulose fibers, i.e. the covalent bond formation.

Wet Strength Improvement of TEMPO-Oxidized Cellulose Sheets Prepared with Cationic Polymers

Cellulose fibers were oxidized with a catalytic amount of 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) in water, and these TEMPO-oxidized cellulose fibers were subjected to sheet making with cationic polymers such as cationic poly(acrylamide) (C-PAM) and poly(vinylamine) (PVAm). The wet strength of the sheets thus prepared was evaluated in terms of the cationic polymer used. It was found that wet tensile strength of the sheets was clearly improved by the cationic polymer addition to the cellulose slurries. Especially, the C-PAM addition was effective in wet strength improvement of the sheets, when the TEMPO-oxidized cellulose fibers were used. The results obtained using the TEMPO-oxidized and then NaBH4-reduced cellulose fibers showed that aldehyde groups present in the TEMPO-oxidized cellulose fibers have some interactions with the cationic polymers in the sheets, contributing to their wet strength improvements. Hemiacetals, N-acylcarbinolamines, carbinolamines, and Schiff bases are the possible s...

Preparation and properties of alginate/carboxymethyl chitosan blend fibers

Alginate/carboxymethyl chitosan blend fibers, prepared by spinning their mixture solution through a viscose-type spinneret into a coagulating bath containing aqueous CaCl 2, were studied for structure and properties with the aid of infrared spectroscopy (IR), X-ray diffraction (XRD) and scanning electron micrography (SEM). The analyses indicated a good miscibility between alginate and carboxymethyl chitosan, because of the strong interaction from the intermolecular hydrogen bonds. The best values of the dry tensile strength and breaking elongation were obtained when carboxymethyl chitosan content was 30 and 10 wt%, respectively. The wet tensile strength and breaking elongation decreased with the increase of carboxymethyl chitosan content. Introduction of CM-chitosan in the blend fiber improved water-retention properties of blend fiber compared to pure alginate fiber. Antibacterial fibers, obtained by treating the fibres with aqueous solution of N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride and silver nitrate, respectively, exhibited good antibacterial activity to Staphylococcus aureus.

Ion-exchange behavior of carboxylate groups in fibrous cellulose oxidized by the TEMPO-mediated system

When native cellulose is treated by catalytic oxidation with 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)/NaBr/NaClO under aqueous conditions, significant amounts of carboxylate and aldehyde groups can be introduced on surfaces of cellulose I crystallites and into disordered regions without any changes in crystallinity of cellulose I or in the original fibrous morphology. In this study, behavior of ion exchange of carboxylate groups in the TEMPO-oxidized fibrous cellulose prepared from cotton linters was compared with that of fibrous carboxymethyl cellulose (F-CMC) with almost the same carboxylate content as that of the TEMPO-oxidized cellulose. These fibrous celluloses were soaked in various metal salt solutions, and metal ion contents in the celluloses were determined by X-ray fluorescence analysis after washing with water and drying of the celluloses. In all metal salts examined in the ion-exchange experiments, the TEMPO-oxidized cellulose had metal ion contents higher than those of F-CMC. Especially, lead, calcium and silver ions were greatly introduced into the TEMPO-oxidized cellulose with the metal ion/carboxylate molar ratio of about 1:1. The adsorption selectivity of metal ions on the TEMPO-oxidized cellulose was also studied using aqueous solutions containing multiple metal salts for soaking, and the following selectivity order was obtained: Pb 2+>La 3+>Al 3+>Cu 2+>Ba 2+>Ni 2+>Co 2+>Cd 2+, Sr 2+, Mn 2+, Ca 2+>Mg 2+ Moreover, swelling ability of the TEMPO-oxidized celluloses having various metal carboxylate groups in water and wet tensile strength of handsheets prepared thereof were studied in terms of kinds of metal ion introduced. Degree of dissociation of the metal carboxylate groups in these celluloses is likely to affect the results of the above characteristics of the TEMPO-oxidized celluloses.

Preparation and Properties of Alginate/Water‐Soluble Chitin Blend Fibers

Water‐soluble chitin (half‐deacetylated chitin) was prepared from chitosan by N‐acetylation with acetic anhydride. Alginate/water‐soluble chitin blend fibers were prepared by spinning their mixture solution through a viscose‐type spinneret into a coagulating bath containing aqueous CaCl2 and ethanol. The structure and properties of the blend fibers were studied with the aids of infrared spectra (IR), X‐ray diffraction (XRD) and scanning electron microscopy (SEM). structure analysis indicated good miscibility existed between alginate and water‐soluble chitin, due to the strong interaction from the intermolecular hydrogen bonds and electrostatic interactions. Best values for the dry tensile strength and breaking elongation were obtained when the water‐soluble chitin content was 30 wt%. The wet tensile strength and breaking elongation decreased with the increase of water‐soluble chitin content. The introduction of water‐soluble chitin in the blend fiber can improve the water‐retention properties of the blend fiber compared to pure alginate fiber. The fibers treated with aqueous solution of silver nitrate have good antibacterial activity to Staphylococcus aureus.

Composite sheets with biodegradable polymers and paper, the effect of paper strengthening agents on strength enhancement, and an evaluation of biodegradability

AbstractComposite sheets composed of biodegradable polymers (BP) and paper were prepared, and their physical and biodegradable properties were investigated. The paper sheets were soaked in BP emulsions and cured at 100°C for 20 min. The wet strength of composite sheets with the same basis weight increased significantly with increasing BP content, although dry strength increased only moderately. A 0.5% addition of a common wet paper‐strengthening agent, poly(amidoamine‐epichlorohydrin) (PAE) resin, enhanced the wet strength, which reached 9.3 MPa, of composite sheets consisting of a BP : paper ratio of 20 : 80. Further enhancement was achieved by the addition of polyvinylamines (PVAm). The wet tensile strength of composite sheets consisting of BP and paper (20 : 80) increased by 27% with the addition of 0.2% PVAm and 0.5% PAE, whereas it was enhanced by only 3–4% with the addition of 0.7% PAE. The biodegradability of the composite sheets was somewhat retarded by the addition of PAE and PVAm. However, a 90% weight loss was observed 60 days after placing composite sheet samples in soil. A similar weight loss was observed after 45 days for composites without additives and after 30 days for base paper alone. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 861–866, 2005

Crosslinking and Agent Distribution of Cotton Cellulose Treated with Combined Dimethylolethyleneurea and Dimethylol-N,N'-dimethylene-tris-ethyleneurea

We have used three different processes to treat cotton fabrics with different combined weight ratios of dimethylolethyleneurea (DMEU) and dimethylol-N,N'-dimethylene-tris ethyleneurea (DMDME3EU) as crosslinking agents, and have found that a two-step process of pad(DMDME3EU)-dry-cure-pad(DMEU)-dry-cure yields higher dry crease recovery angles (DCRA), wet crease recovery angles (WCRA), and equilibrium direct dye adsorption values than the other two processes of pad(DMEU)-dry-cure-pad(DMDME3EU)-dry-cure and pad- (mixture of DMEU and DMDME3EU)-dry-cure at the same nitrogen content and a combined ratio of equal concentrations of the two agents. The process of pad(DMDME3EU)-dry-cure- pad(DMEU)-dry-cure also yields higher DCRA values for a given wet crease recovery angle and tensile strength retention and an even crosslinking agent distribution in/on the treated fabrics. At the same time, the DCRA and WCRA values for the pad(DMDME3EU)-dry-cure- pad(DMEU)-dry-cure process are higher than those for the other two processes at a given number of crosslinks per anhydroglucose unit.

Physical properties and reaction kinetics of cotton cellulose crosslinked with dimethyloldihydroxyethyleneurea–maleic acid

AbstractTwo dicarboxylic acids were used to join with dimethyloldihydroxyethyleneurea (DMDHEU) as crosslinking agents to treated cotton fabrics. These results reveal that the dry crease recovery angle values of the treated fabrics for DMDHEU–maleic acid are higher than those for DMDHEU–tartaric acid at a given wet crease recovery angle and tensile strength retention. The IR spectra show that the reaction between the –OH of DMDHEU and cellulose and the vinyl groups of maleic acids occurred. The cross section of the DMDHEU–maleic acid and DMDHEU–tartaric acid treated fibers and the energies of activation and other data of reaction kinetics for DMDHEU–maleic acid and DMDHEU–tartaric acid strongly suggest that the reaction of vinyl groups of maleic acid with cellulose molecules can take place during the pad/dry‐cure process. Additionally, the surface distribution of crosslinking agent on the finished fabrics for DMDHEU–maleic acid is slightly lower than that for DMDHEU–tartaric acid. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3886–3893, 2004

Effects of various sterilization methods on the setting and mechanical properties of apatite cement.

Sterilization capability is a necessary requirement for any material that is to be used in a medical application. Therefore, it is necessary for apatite cement (AC) to be sterilized. Because there is little information on the sterilization methods of AC, the aims of this investigation were to evaluate the effects of various sterilization methods, including steam, dry heat, ethylene oxide (EtO) gas, and gamma irradiation sterilizations, on the setting and mechanical properties of AC. In the case of steam sterilization, because AC powder aggregated before setting-time measurements, the setting time could not be measured. When the powder was sterilized by dry heat or EtO gas, the setting time was prolonged significantly and the wet diametral tensile strength (DTS) value decreased significantly. Therefore, sterilizations with steam, dry heat, or EtO gas were suggested to be inappropriate methods for AC. Accordingly, the following experiments focused on gamma sterilization. The setting time of AC was retarded with an increase in gamma irradiation dose. The wet DTS value decreased with the increase in gamma irradiation dose. There was no compositional change due to the gamma irradiation. The following tests were carried out in order to examine the effect of the gamma irradiation on the setting reaction of AC in detail. Tetracalcium phosphate [TTCP: Ca(4)(PO(4))(2)O] and dicalcium phosphate anhydrous (DCPA: CaHPO(4)) were separately irradiated, and the cements were produced with the use of irradiated powder and nonirradiated powder. Although the wet DTS value of AC produced from irradiated TTCP and nonirradiated DCPA decreased with increasing gamma irradiation dose, there was no significant difference. In contrast, the wet DTS value of AC produced from irradiated DCPA and nonirradiated TTCP significantly decreased with the increase in gamma irradiation dose. In conclusion, although the detailed mechanism of the delayed setting time and decreased DTS value was not clarified by the present study, it was found that gamma irradiation affected DCPA more than TTCP.

Crosslinking of cotton cellulose in the presence of alkyl diallyl ammonium salts. I. Physical properties and agent distribution

AbstractWe used three kinds of alkyl diallyl ammonium salts (methyl, ethyl, and propyl) in combination with dimethyloldihydroxyethyleneurea (DMDHEU) as crosslinking agents. The nitrogen content, dry crease recovery angle (DCRA), moisture regain, and wicking height for the DMDHEU/alkyl diallyl ammonium salts were in the order of CH3 > C2H5 > C3H7, but the wet crease recovery angle (WCRA) and tensile strength retention (TSR) were in the opposite order at the same resin concentration. For the same DCRA and TSR, the WCRA values for only DMDHEU were lower than those for DMDHEU/alkyl diallyl ammonium salts, and the WCRA values for DMDHEU/alkyl diallyl ammonium salts were in the order of C3H7 > C2H5 > CH3. Both the OH group of the cellulose and DMDHEU could react with the vinyl or epoxy groups of the alkyl diallyl ammonium salts during the pad–dry–cure process. The surface migration for DMDHEU/alkyl diallyl ammonium salts was in the order of CH3 > C2H5 > C3H7. Fabrics treated with DMDHEU/alkyl diallyl ammonium salts showed good antibacterial properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1662–1669, 2003

Crosslinking of Cotton Cellulose in the Presence of Alpha-Amino Acids

We have used alpha-amino acids (aspartic acid and glutamic acid) to join with dimethyloldihydroxyethyleneurea (DMDHEU) as crosslinking agents, and have found that at a given resin concentration, the wet crease recovery angle (WCRA) and tensile strength retention (TSR) values of the treated fabrics are in the order of DMDHEU- glutamic acid > DMDHEU-aspartic acid > DMDHEU; however, the dry crease recovery angle (DCRA) values are in the inverse rank. Nitrogen content and wicking height (wH) values for the various finished fabrics rank as DMDHEU-aspartic acid > DMDHEU- glutamic acid > DMDHEU. We have also found that the WCRA and DCRA of DMDHEU- alone treated fabrics are lower than those of the DMDHEU-alpha-amino-acid treated fabrics, and are ranked as DMDHEU-glutamic acid > DMDHEU-aspartic acid > DMDHEL' alone at a given TSR. The reaction between the —OH of DMDHEU and the amino and acid groups of alpha-amino acids in a pad-dry-cure process are confirmed by IR spectra. Surface distribution of the crosslinking agent on the finished fabrics is similar for DMDHEU alone and DMDHEU-alpha-amino acid.

Calcium hypochlorite as a disinfecting additive for dental stone

Statement of problem Dental casts come into direct contact with impression materials and other items that are contaminated by saliva and blood from a patient’s mouth, leaving the casts susceptible to cross-contamination. Topical methods of disinfecting casts are difficult to control, while immersion methods are potentially destructive. Thus, an additional method to control cross-contamination between patients and laboratory personnel is needed. Purpose This study was undertaken in an attempt to develop a dental stone with disinfecting properties and adequate compressive and tensile strengths. Material and methods Calcium hypochlorite [Ca(OCl) 2] in aqueous solution in concentrations from 0 to 1.5% was tested as a disinfecting additive to type V dental stone. The compressive and tensile strength properties of the modified stone were measured (MPa) using a universal testing machine at a consistency similar to unmodified stone. Strength data were analyzed by 1-way ANOVA and post hoc Tukey-Kramer procedure (α ≤ .05). To measure the disinfecting ability, the effect on Bacillis subtilis bacteriophage phi29 was tested in triplicate to find the minimum concentration at which no phage was detected. Additionally, 3 impressions were disinfected with CaviCide, and 3 impressions rinsed in water served as controls. Results In general, the effect of adding the disinfectant to the stone was a decrease in strength. Exceptions were the dry compressive strength, for which there was a significant increase in strength ( P=.048) at 0.5%, and the wet compressive and wet tensile strength, which showed no significant difference between the 1.5% and the control. When Ca(OCl) 2 was added at the concentration 0.5% (2765 ppm available chlorine), the gypsum had acceptable mechanical properties; dry compressive strength was 78.86 ± 4.12 MPa, and dry tensile strength was 10.64 ± 1.27 MPa, compared to control values of 67.85 ± 6.28 and 13.41 ± 1.24 MPa, respectively. At concentrations of 0.3% and higher (36 1650 ppm of available chlorine), calcium hypochlorite was able to completely inactivate phi29. Conclusion It is possible to prepare a type V dental stone that contains a disinfectant, has adequate mechanical properties, and will reduce numbers of residual microorganisms. For example, stone mixed with water containing 0.5% Ca(OCl) 2 meets these criteria.

Physical Properties of Lyocell Fibers Spun from Isotropic Cellulose Dope in NMMO Monohydrate

This article describes the physical properties of lyocell fibers spun from an isotropic cellulose spinning dope in N-methyl morpholine N-oxide (NMMO) monohydrate (IPS lyocell fibers). Wide angle x-ray diffraction (wAxD) experiments on the crimped fibers exhibit little difference in the crystal structure of IPS and Tencel lyocell fibers: both fibers reveal a cellulose II structure. However, the IPS lyocell fibers have a lower tensile modulus than Tencel by about 12.5%, although they have a similar tensile strength. Wetting and subsequent drying shift the loss tangent values higher, which is more remarkable for the IPS lyocell fibers dried under tension. Further, the IPS lyocell fibers dried under tension have a sharper α-transition peak than the fibers dried without tension. The IPS lyocell fibers exhibit excellent wet tensile strength: 90% of tensile strength is retained after wetting twice in distilled water. In addition, the IPS lyocell fibers show good chemical stability to acids and alkalis, except for an extremely strong alkali—pH 14. Mercerization of the IPS lyocell fibers in the buffer solution of pH 14 notably decreases the tensile modulus but increases elongation.

A gelatin coated collagen-polyglycolic acid composite membrane as a dural substitute.

We designed a new biodegradable composite membrane for use as a dural substitute. This membrane is composed of polyglycolic acid (PGA) mesh, collagen sponge, and gelatin sponge. Collagen layers are attached on both sides of the PGA mesh. One side of the membrane is coated with freeze-dried gelatin to prevent tissue adhesion. We examined the mechanical properties of the membrane and evaluated its efficacy in vivo by implanting it into dogs. When the mechanical properties of the membrane were measured under wet conditions, tensile strength and resistance against cutting by a suture were approximately 20 N/cm and 13 N, respectively, which are adequate for a surgical material. In the in vivo experiment, our dural substitute was implanted into six adult beagle dogs to repair a 25 x 15 mm defect in the dura mater. Two dogs each were killed at 2 and 4 months after implantation and two were observed over 6 months. At 4 months after implantation, the implanted dural substitute was almost absorbed and a fibrous membrane resembling native host dura had regenerated at the site. No foreign body reaction or significant adhesion to the cerebral cortex was observed. These results indicate the clinical potential of our novel dural substitute.

Wet strength improvement of unbleached kraft pulp through laccase catalyzed oxidation

Previous investigations have shown that laccase catalyzed oxidation of lignin containing wood fibers can enhance the strength of medium density fiberboards. In the present work it was investigated if laccase treatment had any impact on the tensile strength of a high yield unbleached kraft pulp. Treatment with laccase alone had only a very little effect on the wet strength of the pulp, whereas addition of lignin rich extractives increased the wet strength after the enzyme treatment significantly. A mediated oxidation gave a similar improvement of the wet tensile strength although no lignin was added to the fiber suspension. Furthermore, it was found that a heat treatment combined with a mediated oxidation gave a higher improvement in wet tensile strength than could be accounted for by the individual treatments. No change in dry tensile strength from the laccase treatment was observed. It is suggested that the observed improvement in wet tensile strength is related to polymerization of lignin on fibers in the hand sheet and/or coupling of phenoxy radicals on lignin associated to adjacent fibers. For the different mediators studied, a correlation was found between oxygen consumption upon mediated oxidation and generation of wet strength in the pulp.

Advanced membranes for alkaline primary and rechargeable alkaline cells with zinc anodes

Several advanced cellulosic and radiation grafted polypropylene membrane materials are currently under evaluation in the laboratories at Navsea Crane and Rutgers University, for application to alkaline primary and rechargeable cell chemistries which employ zinc as the anode material. A portion of these tests involve model cell evaluations of cellulosic membranes for silver migration rates through the membranes as a function of separation layers and changes in the degree of polymerisation (DP), wet tensile strength (WTS) and voltage changes at both electrodes as a function of model rechargeable cell life cycle. Other testing on the actual membranes is generating data for both cellulosic and polypropylene materials on impedance, swelling properties, and silver and zinc penetration rates. The overall goal of these investigations is to obtain candidate separation membranes which will reduce zinc anode shape change and shedding and resist alkaline oxidative degradation to extend the active wet life in primary cells and both wet and life cycle in rechargeable cells.

Experimental Manufacture of Paper for War Maps.

Early in World War II, a new map paper was developed that greatly improved the quality and performance of war maps. The National Bureau of Standards cooperated in the development and, subsequently, determined by experimental manufacture how to make the paper from commercially available raw materials. The best results were obtained in experimental manufacture by using fiber furnishes of 100-percent strong bleached sulfate pulps with the addition of melamine-formaldehyde resin to increase the wet strength and titanium dioxide to produce the desired capacity. It was essential that the beating be very carefully controlled to preserve the maximum fiber strength. The most critical requirements from a manufacturing standpoint were very high resistance to tear, high wet tensile strength, high opacity, and good smoothness. A moderate degree of wildness was not objectionable. The data obtained by experiments were applied to initiate the commercial production of the new paper to meet unprecedented tonnage requirements.

Chemical Modification of Chemithermomechanical Pulps Part 1: Mechanical, Optical, and Aging Properties of Propionylated Spruce CTMP

The effect of propionic anhydride on the optical, mechanical, and aging properties of hydrogen-peroxide-bleached spruce (Picea abies) chemithermomechanical pulp (CTMP) has been examined. The aging properties were evaluated using different aging conditions simulating aging behind window-glass, ambient storage (in the dark), and dry heat exposure. The propionylation treatment was carried out on paper sheets. Chemical modification with propionic anhydride strongly reduced light-induced yellowing: Up to 80% of the discoloration (calculated from the post color number) could be hindered, although 50% of the free phenolic hydroxyl groups were still present in the propionylated sample. The stability against storage in the dark under ambient conditions (23°C, 50% relative humidity) or exposure to dry heat (105°C) was, however, not improved to the same extent. Propionylation did not extensively change the optical or dry strength properties of the treated paper sheets, whereas the wet tensile strength was substantially improved.

Effect of blending tricalcium phosphate on hydrolytic degradation of a block polyester containing poly(L-lactic acid) segment

The effect of blending tricalcium phosphate (TCP) on hydrolytic degradation of a new type of poly(L-lactic acid)/poly(ethylene;hexamethylene/ sebacate) block polyester (60 : 40 wt%) was studied. 100- and 250-μm film specimens blended with 0, 10, and 30 wt% TCP were immersed in phosphate buffered saline (pH 7.4) at 37°C for up to 80-104 weeks. At appropriate intervals, water absorption, dry and wet tensile strength, molecular weight, and thermal properties of the specimens were measured by weighing, tensile strength testing, size exclusion chromatography, and differential scanning calorimetry, respectively. Some samples were characterized by H NMR spectroscopy. Blending of TCP with the block polyester was effective in retarding degradation. The blended TCP was thought to retard degradation for the most part by neutralizing the lactic acid oligomers produced by hydrolysis of the poly(lactic acid) part during the initial stage of degradation.

Degradation of composite materials composed of tricalcium phosphate and a new type of block polyester containing a poly(L-lactic acid) segment

Degradation of a new type of poly(L-lactic acid)/poly(ethylene; hexamethylene/sebacate) block polyester and its composite containing 10 and 30 wt% tricalcium phosphate (TCP) were studied in vitro. Film specimens of thickness 100 and 25() μm for each of the three materials were immersed in phosphate buffered saline (pH 7.4) at 37°C for up to 24 weeks. At appropriate intervals, water absorption, dry and wet tensile strength, molecular weight, and thermal properties of the specimens were measured by weighing, tensile strength testing, size exclusion chromatography. and differential scanning calorimetry, respectively. The decrease in tensile strength was greater in the unblended and thicker polymer film than in the other five films. The retention of tensile strength after 24 weeks increased with increasing TCP content. This trend was also noticed in the retention of molecular weight. The tensile strength of the materials having molecular weights below 5 x 104-6 x 104 Mw or 2 x 104-3 x 104 Mn dropped substantially and the materials became fragile. Blending of TCP to the PLLA block polyester retarded degradation, suggesting that TCP neutralized the carboxyl end groups formed by hydrolysis of ester bonds.