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Temperature Dependence on Gas Permeability and Permselectivity of Poly(Lactic Acid) Blend Membranes

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Temperature Dependence on Gas Permeability and Permselectivity of Poly(Lactic Acid) Blend Membranes #2009 The Society of Polymer Science, Japan NOTE Temperature Dependence on Gas Permeability and Permselectivity of Poly(lactic acid) Blend Membranes By Tomomi KOMATSUKA1 and Kazukiyo NAGAI1;Ã KEY WORDS: Biodegradable / Poly(lactic acid) / Permeability / Permselectivity / Separation Factor / Glass Transition / Membrane / Poly(lactic acid) (PLA, Scheme) is an environmentally friendly and biodegradable polymer substance (1). Due to the − R − O − advantages it offers including better biological degradation n behavior for bio-recyclable materials, PLA is expected to H H H become a replacement material for petroleum-based plastics, CH3 such as polyethylene, polyvinylchloride, and poly(ethylene R : − C − C − − C − C − − Si − terephthalate). At present, PLA is popularly used in the CH manufacture of packaging materials (e.g., films, membranes), CH3 O CH3 H 3 foaming materials (e.g., containers), and resins. These materi- als are expected to be used at high temperatures in several PLA PPO PDMS applications such as in films and containers for heating frozen Scheme 1. foods in microwave ovens and a retort in boiling water, and in resins for the bodies of electronic products (e.g., computers and mobile phones). Toward further improvements, it is important employed in our previous study (4). These were kindly to emphasize that the mechanical, thermal, and barrier proper- prepared by Asahi Kasei Life & Living Co., Ltd., Suzuka, ties are important in designing these materials. Japan. The base PLA polymers were L96D4 (L-donor 96 mol %, There are some studies about temperature dependence on D-donor 4 mol %) and L88D12 (L-donor 88 mol %, D-donor gas permeability and permselectivity of PLA homopolymers 12 mol %). PLA membranes with different crystallinities were below their glass transition temperature (i.e., glassy state) (2,3). prepared by blending these two polymers; Blend 8/2 However, there has been no research to date on the gas (L96D4:L88D12 = 8:2, Thickness: 24 Æ 1 mm) and Blend 10/0 permeability and permselectivity of PLA homopolymers and (L96D4 homopolymer, L96D4:L88D12 = 10:0, Thickness: blends above their glass transition temperature (i.e., rubbery 27 Æ 2 mm). state). The same is the case for gas permeation and separation The glass transition temperature (Tg) values of the Blend behavior across the glass transition of PLA homopolymers and 10/0 and Blend 8/2 membranes were 62.3 C and 60.5 C, blends. respectively. The crystallization temperature (Tc) values of the In this study, the temperature dependence on gas perme- Blend 10/0 and Blend 8/2 membranes were 117 C and ability and permselectivity of PLA blends across their glass 116 C, respectively. The melting temperature (Tm) value of transition temperatures is therefore investigated for the first both blend membranes was 149 C. The crystallinity (Xc) time. PLA is an interesting polymer whose oxygen perme- value, which was determined from differential scanning ability is not significantly affected by its isomer ratio and calorimeter of the Blend 10/0 membrane, was 24.8%, while crystallinity (2–4). In the ranges of the L:D donor ratio of that of the Blend 8/2 membrane was 7.4%. 98.7:1.3–50:50 and crystallinity of 0–25%, the oxygen perme- ability coefficients of the PLA samples were located in the Gas Permeation Measurements values between 1:7 Â 10À11 and 3:4 Â 10À11 cm3(STP)cm/ The permeability coefficient (P) of pure gases (i.e., hydro- 2 (cm s cmHg) at 30–35 C. The PLA samples used in this study gen (H2), oxygen (O2), nitrogen (N2), and carbon dioxide were those with properties within above ranges. (CO2)) in the PLA blend membranes was determined using a constant-volume/variable-pressure method according to the EXPERIMENTAL literature (5). The operating temperature was raised from 35 Æ 1 to 85 Æ 1 C, which was much below Tc (i.e., there was Materials only the glass transition for PLA in this temperature range.). The PLA membranes we used were the same samples The feed pressure was between 39 and 75 cmHg and the 1Department of Applied Chemistry, Meiji University, 1-1-1 Higashi-mita, Tama-ku, Kawasaki 214-8571, Japan ÃTo whom correspondence should be addressed (Tel: +81-44-934-7211, Fax: +81-44-934-7906, E-mail: [email protected]). Polymer Journal, Vol. 41, No. 5, pp. 455–458, 2009 doi:10.1295/polymj.PJ2008266 455 T. KOMATSUKA and K. NAGAI permeate side was maintained under vacuum. All permeation 10-8 data were determined for at least three samples to ensure the T g reproducibility of the experimental results. In addition, the experiments were repeated at least thrice for each sample at a H -9 2 given temperature to confirm the reproducibility. 10 The ideal permselectivity of Gas A over Gas B ( (A/B)) s cmHg)) 2 CO was expressed as the ratio of the permeability coefficient of 2 Gas A over that of Gas B. 10-10 O 2 PðAÞ ðA=BÞ¼ ð1Þ PðBÞ (STP)cm/(cm 3 -11 N 10 2 RESULTS AND DISCUSSION P (cm (a) Blend 10/0 -12 Figure 1 presents the temperature dependence on the 10 2.7 2.8 2.9 3.0 3.1 3.2 3.3 permeability coefficients for H2,O2, and N2, and CO2 in 1 3 -1 x 10 (K ) Blend 10/0 and Blend 8/2 membranes. During the experiments T in this study, any hysteresis in the permeation data in both 10-8 Blend 10/0 and Blend 8/2 membranes was not observed. In the T whole temperature range used, the order of the permeability g coefficients was the same for all gases for both Blend 10/0 and H -9 2 Blend 8/2 membranes: H2 > CO2 > O2 > N2. Additionally, 10 as the temperature increased, all gas permeability coefficients s cmHg)) increased. 2 CO 2 In the region without any transition in polymers (e.g., glass 10-10 e.g. O transition) and penetrant ( , boiling point), the temperature 2 dependence on gas transport through a polymer membrane (STP)cm/(cm generally follows Arrhenius rule (6). That is, there is a linear 3 10-11 N relationship between a transport parameter logarithm and the 2 reciprocal of absolute temperature (T). P is expressed as P (cm (b) Blend 8/2 EP -12 P ¼ P0 exp À ð2Þ 10 RT 2.7 2.8 2.9 3.0 3.1 3.2 3.3 1 3 -1 where P0 is the pre-exponential factor of permeation, EP is the x 10 (K ) activation energy for permeation, and R is the gas constant. T Across polymer Tg, there appears a transition on gas perme- Figure 1. Temperature dependence on gas permeability (P) in (a) Blend 10/0 and (b) Blend 8/2 poly(lactic acid) (PLA) membranes. ation. Therefore, the EP value of gases in polymers is either Gases: ,H2; ,CO2; ,O2; ,N2. larger or smaller above Tg than below Tg. Sometimes, no transition is observed; that is, the EP values at above Tg and below Tg are the same with each other. entire experimental temperature range (i.e., 35–85 C), because In Figure 1, both Blend 10/0 and Blend 8/2 membranes we could not observe a distinct transition on gas permeation at followed Arrhenius rule for all gases tested in this study. When their Tg. This means that these P0 and EP values above Tg were experimental uncertainty was considered, it was difficult to the same as those below Tg. Gas permeability is significantly indicate a distinct transition of gas permeability at Tg. influenced by measurement temperature and feed gas pressure. Otherwise, the uncertainties might mask a small transition on Moreover, although a simple comparison between our blend permeation. We have found that Blend 10/0 and Blend 8/2 data and the homopolymer values in the literature was difficult, membranes belong to a family of polymers whose gas for O2, and N2, and CO2, Blend 10/0 and Blend 8/2 permeation is not significantly affected by a change in chain membranes had larger P0 and EP values compared with those mobility at glass transition. of glassy PLA homopolymers. Table I summarizes the permeability coefficients at around The following empirical equation describes the relationship room temperature (PðTÞ), P0, and EP for H2,O2, and N2, and between log P0 and EP=R (9). CO in Blend 10/0 and Blend 8/2 membranes with some data 2 E from the literature (2,3,7,8). All literature data on PLA log P ¼ P Â 10À3 þ Z ð3Þ 0 R homopolymers were recorded below Tg. There were no data for hydrogen in PLA homopolymers from the literature. We Regardless of the chemical structures of common polymers, the À3 estimated the P0 and EP values of our samples through the plot of log P0 and EP=R provides the slope of 1 Â 10 and the 456 #2009 The Society of Polymer Science, Japan Polymer Journal, Vol. 41, No. 5, pp. 455–458, 2009 Temperature Dependence on Gas Permeability of PLA Blends Table I. Permeation parameters of hydrogen (H2), oxygen (O2), nitrogen (N2), and carbon dioxide (CO2) of Blend 10/0 and Blend 8/2 poly(lactic acid) (PLA) and related polymers Temperature Temperature Crystallinity PðT Þ P0 E Gas Polymer for P(T) range P Reference (%) cm3 ðSTPÞcm cm3 ðSTPÞcm (kJ/mol) (C) cm2 ÁsÁcmHg (C) cm2 ÁsÁcmHg À10 À4 H2 PLA (Blend 10/0) 24.8 35 6:23 Â 10 35–85 3:09 Â 10 33.5 This work PLA (Blend 8/2) 7.4 35 6:77 Â 10À10 35–85 2:43 Â 10À5 27.0 This work PPO 0 30 1:26 Â 10À8 30–80 1:49 Â 10À4 23.6 7 PDMS 0 25 5:73 Â 10À8 25–125 1:73 Â 10À5 14.1 8 À10 À2 CO2 PLA (Blend 10/0) 24.8 35 1:27 Â 10 35–85 2:13 Â 10 48.9 This work PLA (Blend 8/2) 7.4 35 1:21 Â 10À10 35–85 1:14 Â 10À3 41.5 This work PLA (L:D = 98.7:1.3) < 4% 30 1:10 Â 10À10 22.8–45.0 1:46 Â 10À7Ã 18.1 3 PLA (L:D = 80:20) 0 30 5:1 Â 10À11 22.8–45.0 6:0 Â 10À8Ã 17.8 3 PLA (L:D = 50:50) 0 30 7:1 Â 10À11 22.8–45.0 2:1 Â 10À8Ã 14.3 3 PLA (L:D = 98:2) 40 35 2:32 Â 10À10 25–45 1:03 Â 10À7Ã 15.6 2 PLA (L:D = 94:6) 25 35 1:71 Â 10À10 25–45 3:35 Â 10À7Ã 19.4 2 PPO 0 30 7:06 Â 10À8 30–80 1:23 Â 10À5 13.0 7 PDMS 0 25 2:85 Â 10À7 25–125 4:81
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