LCP Content Research Articles

Long-chain polyunsaturated fatty acids in preterm infants: Status at birth and its influence on postnatal levels

To determine the influence of the prenatal long-chain polyunsaturated fatty acid (LCP) supply on prenatal growth and on postnatal LCP levels, we studied 52 preterm infants and assessed the relations between the LCP status at birth (reflecting the prenatal LCP supply), gestational age and prenatal growth, and the relation between the LCP status at birth and at 37 to 42 weeks of gestational age. After a correction for gestational age at birth, significant relations ( p ≤0.05) were observed between anthropometric measurements at birth (weight, head circumference, and length) and LCP levels in the umbilical artery wall, the LCP content of which reflects the long-term fetal LCP status. Independent of the neonatal diet (human milk or formula), LCP levels in erythrocyte phospholipids at term were positively related to levels in the umbilical artery wall (docosahexaenoic acid (22:6 n-3): p ≤0.0003; arachidonic acid (20:4 n-6): p = 0.02). Postnatal diet significantly influenced LCP levels in plasma phospholipids at term (docosahexaenoic acid: p ≤0.004; arachidonic acid: p = 0.02); formula-fed infants had lower values. We conclude that the LCP status of preterm infants at birth is related to prenatal growth. Moreover, next to the postnatal enteral diet, the LCP status at birth significantly affects LCP levels at term postconceptional age. This finding may warrant further studies of the effects of essential fatty acid-enriched maternal diets during pregnancy on the neonatal LCP status at birth. ( J PEDIATR 1995;126:611-8)

Blends of a PPO–PS alloy with a liquid crystalline polymer

AbstractBlends of a PPO–PS alloy with a liquid crystalline polymer have been studied for their dynamic properties, rheology, mechanical properties, and morphology. This work is an extension of our previous work on PPO/LCP blends. The addition of the LCP to the PPO–PS alloy resulted in a marked reduction in the viscosity of the blends and increased processibility. The dynamic studies showed that the alloy is immiscible and incompatible with the LCP at all concentrations. The tensile properties of the blends showed a drastic increase with the increase in LCP concentration, thus indicating that the LCP acted as a reinforcing agent. The tensile strength, secant modulus, and impact strength of the PPO–PS/LCP blends were significantly higher than that of PPO/LCP blends. Morphology of the injection molded samples of the PPO–PS/LCP blends showed that the in situ formed fibrous LCP phase was preserved in the solidified form. A distinct skin–core morphology was also seen for the blends, particularly with low LCP concentrations. The improvement of the mechanical properties of the blends is attributed to these in situ fibers of LCP embedded in the PPO–PS matrix. The improvement in the properties of PPO–PS/LCP over PPO/LCP is also attributed to the addition of the PS which consolidates the matrix. © 1995 John Wiley & Sons, Inc.

Mechanical properties of blends of liquid crystalline copolyesters with polyprophylene

A significant effect of the addition of LCP on the mechanical properties and their anisotropy has been established. Already, if one considers the shape of curves of the stress-strain relationship it can be seen that curves typical for semicrystalline polymers (pure polypropylene) with clearly visible yield point and significant cold drawing leading to an anisotropic stiffening are changing into curves without yielding and with a brittle failure (LC-rich blends). Generally, the tensile elasticity modulus increases with increasing LCP content for both MD and TD. The maximum value of anisotropy of elastic properties was noted for a rather low content of LCP (c = 5%). On the contrary, the stress at yield decreases with increasing LCP content. The same was observed for the strain at yield but in both cases an important increase of anisotropy has taken place. Consequently, the total elongation during drawing (strain at break) showed a drastic decrease for blends with higher LCP content (about 60–80 times). The addition of the LCP to polypropylene has led to a stiffness increase (higher elasticity modulus) but simultaneously to a considerable plasticity decrease. As a confirmation of these observations, there served also the creep test where a decrease of the creep compliance (by two times) for LC-rich blends as compared with pure PP was noted.

Modulation of supramolecular structure of linear polyurethane systems by addition of liquid-crystalline polymers in the molecular miscibility range

The peculiarities of domain structure of segmented polyurethane-urea/liquid-crystalline polyester (PU/LCP) blends were studied in the LCP concentration range of 1–10%, with different lengths of the flexible moiety. Small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry were used. The position of the SAXS maximum changes discontinuously with increasing LCP concentration. We suggest that the rigid fragments of the LCP tend to be incorporated into the rigid domains of the PU component with the restriction that only each third or fourth fragment is involved. The part of the LCP molecule that fits in the space between rigid PU domains is stretched and determines the interdomain distance.

Changes in the Fatty Acid Composition of Preterm and Term Human Milk from 1 Week to 6 Months of Lactation

Using capillary gas chromatography, we analyzed the fatty acid composition of human milk from 23 women who had delivered prematurely and 16 women who had delivered at term. Milk samples were obtained at 1, 2, 4, 12, and 26 weeks after delivery. The relative amounts of saturated and monounsaturated fatty acids in preterm and term milk remained stable throughout the 6 months of lactation. The proportions of linoleate (18:2n-6) and alpha-linolenate (18:3n-3) were similar in preterm and term milk and showed an increasing trend from transitional (8.7-9.9% and 0.9-1.1% of total fatty acids, respectively) to mature milk (9.9-11.8% and 1.2-1.5%, respectively). The proportions of the major long-chain polyunsaturated fatty acids (LCP), 20:3n-6, 20:4n-6, 22:5n-3 and 22:6n-3, were highest at 1 week and decreased thereafter in both types of milk. In term milk, the proportion of LCP continued to decrease from 1 month to 6 months, whereas in preterm milk it was fairly constant. Consequently, at 6 months of lactation, the relative content of arachidonate (20:4n-6) was 1.5 times (p < 0.05) and that of docosahexaenoate (22:6n-3) was two times higher (p < 0.01) in preterm than in term milk. We conclude that in long-term lactation, preterm human milk provides a significantly higher relative supply of LCP than term human milk. This higher LCP content may be of special benefit to the development of a preterm infant.

Changes in the Fatty Acid Composition of Preterm and Term Human Milk from 1 Week to 6 Months of Lactation

Using capillary gas chromatography, we analyzed the fatty acid composition of human milk from 23 women who had delivered prematurely and 16 women who had delivered at term. Milk samples were obtained at 1, 2, 4, 12, and 26 weeks after delivery. The relative amounts of saturated and monounsaturated fatty acids in preterm and term milk remained stable throughout the 6 months of lactation. The proportions of linoleate (18:2n‐6) and α‐linolenate (18:3n‐3) were similar in preterm and term milk and showed an increasing trend from transitional (8.7–9.9% and 0.9–1.1% of total fatty acids, respectively) to mature milk (9.9–11.8% and 1.2–1.5%, respectively). The proportions of the major long‐chain polyun‐saturated fatty acids (LCP), 20:3n‐6, 20:4n‐6, 22:5n‐3 and 22:6n‐3, were highest at 1 week and decreased thereafter in both types of milk. In term milk, the proportion of LCP continued to decrease from 1 month to 6 months, whereas in preterm milk it was fairly constant. Consequently, at 6 months of lactation, the relative content of arachidonate (20:4n‐6) was 1.5 times (p &lt; 0.05) and that of docosa‐hexaenoate (22:6n‐3) was two times higher (p &lt; 0.01) in preterm than in term milk. We conclude that in long‐term lactation, preterm human milk provides a significantly higher relative supply of LCP than term human milk. This higher LCP content may be of special benefit to the development of a preterm infant.

Studies on blends of a thermotropic liquid crystalline polymer and polybutylene terephthalate

Structure-property relationships of blends of a thermotropic polyester-type main-chain LCP and polybutylene terephthalate (PBT) were investigated. LCP was melt blended with three different PBTs and the blends were processed by injection moulding or extrusion. Mechanical and thermal properties of the blends were determined and the blend structure was characterized by scanning electron microscopy (SEM). LCP acted as mechanical reinforcement for PBT and improved also its dimensional and thermal stability. The stiffness of PBT increased with increasing LCP content, but at the same time the blends became more brittle. In extrusion the orientation of LCP phases could be further enhanced by additional drawing, which led to significant improvements in strength and stiffness at LCP contents of 20–30 wt.-%.

Blends of Poly(ether ether ketone) with a Thermotropic Liquid Crystalline Polyester I. The Morphology, Crystallization, and Melting Behavior

Blends of poly(ether ether ketone) (PEEK) with a thermotropic liquid crystal copolyester (LCP-111), obtained by solution precipitation, were investigated by optical microscopy and differential scanning calorimetry. The as-precipitated blends underwent phase segregation on heating, as being evident by the microscopy observation. The phase morphologies, melting and crystallization behaviors of the blends were found to be affected by the LCP composition, showing smaller crystal size, slight depression of Tm and higher degree of crystallinity with increasing LCP content. When isothermally crystallized from the melt, a maximum overall rate of crystallization was found for the blend containing about 20 wt% of LCP. The results were discussed in terms of competition between the nucleation and dilution effects of LCP on the crystallization of PEEK.

Orientation and mechanical properties of PBT and its blends with a liquid‐crystalline copolyester

AbstractBlends of poly (butylene terephthalate) (PBT) and a liquid‐crystalline copolyester (60 mol % poly(p‐hydroxy benzoic acid)/40 mol % polyethylene terephthalate) (LCP) were prepared in the melt state. The investigation of mechanical properties indicated that, for the processing conditions used, neither the addition of up to 30 wt % LCP to PBT nor the cooling history affected significantly the tensile modulus E. For oriented specimens, a marked improvement of E was obtained for all the blends, and increased with the LCP content. This improvement was more marked for slowly cooled samples. X‐ray diffraction was used to quantify the orientation of the crystalline PBT and liquid‐crystalline LCP phases. It was shown that neither the thermal history nor the presence of up to 30 wt % LCP affected the orientation behavior of the PBT crystalline phase. For the LCP phase, measurements were not possible for concentrations lower than 10 wt %, and were more difficult and less precise than for PBT. Nevertheless, it was possible to show that a better orientation was obtained for the slowly cooled samples and for higher concentrations of LCP in the blends. This correlated with the enhancement of mechanical properties observed for the oriented samples.

Processing and Properties of Polycarbonate/Liquid Crystal Polymer Blends

Abstract Rheological and mechanical properties, structural characteristics, extrusion and injection molding behavior of blends of polycarbonate (PC) with a thermotropic, wholly aromatic copolyesteramide have been investigated. The processability of polycarbonate is remarkably improved by addition of small contents of liquid crystal polymer. All the flow curves of the blends lie between those of the pure components. In the processing conditions adopted, the LCP particles are easily elongated in the flow direction. In this direction the elastic modulus rises remarkably with LCP content. The modulus-composition curve is, however, lower than that expected on the basis of an additive rule due to the incompatibility and poor adhesion between the two phases. Finally, injection molding of this extrusion grade PC has been easily performed by adding small contents of LCP. The impact strength values of the injection molding samples of these blends are only slightly lower than that of the pure PC.

Rheology, morphology, and mechanical characteristics of poly(etherether ketone)‐liquid crystal polymer blends

AbstractThis paper is in continuation of our previous paper on Poly(etherether ketone)‐liquid crystal polymer (PEEK‐LCP) composites. Rheological, morphological, and mechanical properties of polyetherether ketone and a thermotropic liquid crystalline polymer based on hydroxybenzoic acid/hydroxynaphthoic acid have been reported. Addition of LCP resulted in a marked reduction of viscosity and improved processability. Tensile properties improved with increase in LCP concentration. Synergistic effects have been observed at certain LCP concentrations. The elongation at break was found to reduce drastically above 10% of LCP content. This is a characteristic typical of chopped‐fiber‐filled composites. Morphology of injection molded and capillary extruded samples of the blends showed that the in‐situ formed fibrous LCP phase was preserved in a solidified form. The improvement in tensile properties is likely due to the reinforcement of the PEEK matrix by the fibrous LCP phase as observed by scanning electron microscopy. A distinct skin‐core morphology was found to develop in the injection molded samples of these blends. Mechanical properties measured in the flow and transverse direction indicated an increase in the degree of anisotropy with an increase in LCP content.

Neurohormonal control of cardiac activity in the snail,Helix aspersa

1. The characteristics of a cardioactive peptide(s), LCP, were investigated in the snail,Helix aspersa, to determine if LCP functions as a neurohormone. 2. Fractionation of isotonic homogenates of the auricle and sub-esophageal ganglia indicate that LCP is associated with microsomal elements, probably granules observed in electron micrographs of the microsomal pellets. 3. Ligation experiments carried out under culture conditions suggest that LCP is transported from the sub-esophageal ganglia to the auricle via the visceral nerve. The presence of colchicine in the culture media prevents this transport. 4. LCP is released from the sub-esophageal ganglia and the auricle by incubation in raised K media. This release is largely prevented by lowering the Ca content of the media. 5. LCP is released into the lumen of the auricle by electrical stimulation of the visceral nerve. 6. The ventricle isolated in vitro responds to LCP concentrations similar to those found in the hemolymph. Since the ventricle contains no LCP, this suggests that LCP is carried in the hemolymph from its release site to the ventricle. 7. The combination of these results and those of a preceding paper confirm a role for LCP as a cardioexcitatory neurohormone inHelix.