Comparative Investigation on the Reclamation of NR Based Latex Products with Amines and Disulfides

The latex industry has expanded over the years to meet the world demands for gloves, condoms, latex thread, etc. Due to the strict specifications for the products and the unstable nature of the latex, as high as 15% of the final latex products are rejected. Since waste latex rubber (WLR) represents a source of high quality rubber hydrocarbon, it is a potential candidate for generating reclaimed rubber of superior quality. In the present investigation, two reclaiming agents for WLR vulcanizates were studied in a thermo-mechanical reclaiming process. Parameters investigated were the concentration of the reclaiming agents, as well as reclaiming temperature and time required for proper reclamation. The efficiency of the reclamation process was studied by measurement of the Mooney viscosity, sol-gel analysis and swelling measurements. The ratio of main-chain scission to crosslink scission was studied and the distribution of mono-, di-, and polysulfidic crosslinks was analyzed by thiol-amine reactions. Of the two chemicals investigated, diphenyldisulfide proves itself very effective as reclaiming agent. On the other hand, amines are not suitable as reclaiming agents, because they result in the formation of crosslinks compared to the case where no reclaiming agent is used for reclaiming.

Model Compound Studies on the Devulcanization of Natural Rubber Using 2,3-Dimethyl-2-Butene

The mechanism of devulcanization of sulfur-vulcanized natural rubber with aromatic disulfides and aliphatic amines has been studied using 2,3-dimethyl-2-butene (C6H12) as a low-molecular weight model compound. First C6H12 was vulcanized with a mixture of sulfur, zinc stearate and N-cyclohexyl-2-benzothiazylsulfenamide (CBS) as accelerator at 140 °C, resulting in a mixture of addition products (C6H11−Sx−C6H11). The compounds were isolated and identified by High Performance Liquid Chromatography (HPLC) with respect to their various sulfur ranks. In a second stage, the vulcanized products were devulcanized using the agents mentioned above at 200 °C. The kinetics and chemistry of the breakdown of the sulfur-bridges were monitored. Both devulcanization agents decompose sulfidic vulcanization products with sulfur ranks equal or higher than 3 quite effectively and with comparable speed. Diphenyldisulfide as devulcanization agent gives rise to a high amount of mono- and disulfidic compounds formed during the devulcanization, hexadecylamine, as devulcanization agent, prevents these lower sulfur ranks from being formed.

Release of Dithiocarbamates into Sweat from Natural Rubber Latex Surgical Gloves

The release of zinc dialkyldithiocarbamates from a batch of surgical gloves into the sweat of human subjects was studied. Healthy volunteers from both sexes were asked to don the gloves on both hands for 1 h. The identification and estimation of dithiocarbamate residues released into the sweat were carried out using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The thin layer chromatogram showed that zinc diethyldithiocarbamate (ZDEC) accelerator residues were released into the sweat of volunteers. The estimation by high performance liquid chromatography revealed that the amount of ZDEC released varied among the human subjects despite using the same brand of glove. The effect of sweat rate and pH on the amount of ZDEC released into hand sweat was investigated. The results indicated that it may not be possible to derive a relationship between the sweat-extractable ZDEC and sweat rate or pH of hand sweat. The dithiocarbamate release was studied in the laboratory using a physiologically simulated medium, namely, artificial sweat at different pH levels. The glove was filled with artificial sweat and extracted for 1 h at 37 °C. It was found that amount of artificial sweat-extractable ZDEC varied with changes in pH of artificial sweat. Lack of a clear relationship between the sweat-extractable ZDEC and sweat rate or pH of hand sweat indicated that factors such as hand exercise, glove-fit, etc., may also be considered when simulating actual use conditions in vitro.

Universal newborn hearing screening in Singapore: the need, implementation and challenges

With about 1 in 1000 born with severe to profound hearing loss and about 5 in 1000 with lesser degrees of loss, congenital deafness is the commonest major birth defect. It is the recommended standard that hearing loss in newborns be detected by 3 months of age and intervention implemented by 6 months of age. Delayed detection and intervention may affect speech, language and psychosocial development, resulting in poor academic achievements. Universal newborn hearing screening (UNHS) is the only effective way of detecting all babies with hearing loss, within the recommended time frame. A survey in Singapore revealed that traditional childhood hearing screening programmes resulted in late detection (mean age, 20.8 months; range, 0 to 86 months) and late intervention (mean age, 42.4 months; range, 1 to 120 months). Increasingly, UNHS is becoming standard medical care in developed countries. In Singapore, UNHS has been implemented in all hospitals with obstetric services. Although a screening rate of more than 99% has been achieved in public hospitals, private hospitals have a screening rate of only about 77%. Parents' awareness and acceptance of early detection is still lacking, and this needs to be addressed by appropriate public education. Support from obstetricians and paediatricians will significantly contribute towards this objective. Effective programme management is essential; this includes the use of data management systems, the maintenance of a team of experienced screeners, and efficient coordination between screening and diagnostic services. Early detection of childhood deafness, together with early and effective intervention, maximises the chances of successful integration into mainstream education and society.

Amphidial neurons ADL and ASH initiate sodium dodecyl sulphate avoidance responses in the infective larva of the dog hookworm Anclyostoma caninum

Ablations of specific amphidial neuron pairs with a laser microbeam were conducted to understand better the neurological basis of the behaviours of larval parasitic nematodes. To date, the functions of the amphidial neurons of Caenorhabditis elegans and their counterparts in parasitic nematodes have been found to be remarkably conserved allowing the possibility to predict the relationships between neurons and their functions. Therefore, we anticipated that ablation of neuron pairs ASH and ASK would abrogate avoidance of sodium dodecyl sulphate (SDS) by infective larvae (L3i) of Anclyostoma caninum. Instead, we have found that laser microbeam ablation of these neuron pairs did not eliminate SDS avoidance in A. caninum, but that neuron pairs ASH and ADL are the amphidial neurons responsible for SDS repulsion. When a droplet of the repellent is placed in the direct path of a normal A. caninum L3i, a strong backward avoidance response is triggered. However, when the ASH and ADL neurons are ablated, the nematodes demonstrate the opposite reaction, increasing their movement in a forward direction.

Effect of particle morphology and polyethylene molecular weight on the fracture toughness of hydroxyapatite reinforced polyethylene composite

Fracture toughness testing has been performed on hydroxyapatite-polyethylene composites. Sintered and unsintered grades of hydroxyapatite and two grades of high-density polyethylene were used to make 40 vol % hydroxyapatite composites. Compact tension testing was performed at both room temperature and at 37 degrees C and at three strain rates. The effect of increasing the loading rate from 2 to 200 microm s(-1) was to increase the fracture toughness. Increasing the testing temperature or decreasing the surface area of the reinforcing particles also increased the fracture toughness. However, using a lower molecular weight, injection moulding, grade of polyethylene reduced the fracture toughness. Thus for higher fracture toughness, a low surface area sintered hydroxyapatite in a high-molecular weight polyethylene is required.

Chemical RNA labeling without 3' end bias using fluorescent cis-platin compounds

Recently, fluorescent, monofunctional cis-platin derivatives have been developed to chemically label nucleic acids for use in fluorescent hybridization assays. Here we show by hybridizations to microarrays containing oligonucleotide probes for the 3' ends, middle parts, and 5' ends of mRNAs, that this labeling methodology bypasses the problem of the 3' end bias that is characteristic of the conventional enzymatic oligo(dT)-primed, reverse transcription labeling of mRNAs.

Mass newborn screening in Singapore--position and projections

INTRODUCTION

This paper describes the development, current position and projected development of mass newborn screening in Singapore.

METHODS

A search was conducted through the Medline and through the abstract books of conferences for papers on mass newborn screening in Singapore. This was complemented with the author's own records of the outcome of screening newborns at the National University Hospital.

RESULTS

Cord blood screening for glucose-6-phosphate dehydrogenase (G6PD) deficiency began in 1965; through patient isolation, prompt treatment of jaundice and parent education, kernicterus has been eliminated. Pilot screening for congenital hypothyroidism began in 1981 and has become nationwide since 1990. Screening rates are almost 100% and with early treatment, mental retardation has been eliminated in those affected. However, academic difficulties are present in about a third of patients. Screening for hearing impairment now covers 80% of newborns. The incidence of significant impairment is 1 in 1000 births and interventions have been in place before a year of age. Two strategies--measuring automated auditory brainstem responses (AABR) and otoacoustic emissions supplemented with AABR--are being evaluated.

CONCLUSIONS

The programme requires refining of screening strategies, creation of a central registry of cases, provision of educational support and expansion to include screening with tandem mass spectrometry for multiple inborn errors of metabolism.

Effect of hydroxyapatite morphology/surface area on the rheology and processability of hydroxyapatite filled polyethylene composites

The commercial success of hydroxyapatite (HA) filled polyethylene composite has generated growing interest in improving the processability of the composite. A number of synthetic procedures and post synthesis heat treatment of HA has lead to the availability of powders with widely varying morphological features. This paper addresses the effect of morphological features of HA on the rheology and processability of an injection-moulding grade HA-HDPE composite. The results showed that low surface area HA filled composite exhibited better injection processing characteristics through improved rheological responses. The effect of reducing the surface area of the filler is to require less polyethylene to wet the filler and allows more polyethylene to be involved in the flow processes. These changes reduced the temperatures and pressures required for successful processing.

Maternal thyrotoxicosis causing central hypothyroidism in infants

We describe three infants born to mothers with poorly controlled Graves' disease, who developed transient central hypothyroidism in the immediate postnatal period. Suppression of the fetal pituitary-thyroid axis may be due to placental transfer of thyroxine from the hyperthyroid mother. This may persist for months postnatally, necessitating treatment to optimise neurodevelopmental outcome.

Newborn screening in Singapore

Neonatal screening in Singapore for G6PD deficiency started in 1965. Screening for congenital hypothyroidism started in 1981 as a pilot research program and by 1990, it became nationwide. Screening for congenital hypothyroidism is by the measurement of TSH in the cord serum with recall of those exceeding the 99th percentile, by about 3-4 days of life. Treatment is usually started within a week of life. Over 400,000 newborns have been screened and the screening rate has been about 99.95%. The incidence rate is about 1 in 3,000. G6PD activity in the cord blood is measured using semi-quantitative rapid screening tests. Those identified are physically protected from environmental triggers by keeping them in hospital for a variable period of time. Parents are counseled. Data obtained from 22,830 newborns from the National University Hospital revealed incidence rates of 1.62% in all newborns, 3.15% in males and 0.11% in females. The Chinese and Malay males had a higher (3.94% and 2.95%) incidence respectively when compared to the Indian males with (0.66% incidence). The application of the preventive measures has resulted in no report of kernicterus in the last 20 years. Our efforts are now focused on minimizing the recall rate in the case of hypothyroidism screening, reducing the period of stay in hospital in those with G6PD deficiency and considering the introduction of a PKU screening program in Singapore.

Mass newborn screening for glucose-6-phosphate dehydrogenase deficiency in Singapore

Recognition of kernicterus as a significant contributor to newborn mortality and morbidity in G6PD deficient babies and the ease with which G6PD deficiency could be detected and kernicterus prevented by avoidance of triggers, led to the establishment of mass newborn screening for G6PD deficiency in 1965. G6PD deficient newborns are identified within a day of birth by measuring the enzyme activity in cord blood. They are then physically protected from triggers by keeping them in the hospital for the first 2 weeks of life after their parents are counseled. Enzyme activity is measured using Wong's in-house modification of the Bernstein's technique or the BM G6PD Deficiency Screening test based on the Beutler assay. Close to 1.6 million newborns, representing practically 100% of all births have been screened. Analysis of data from 22,830 newborns at the National University Hospital reveals an incidence of 1.62% in all newborns. 3.15% in males and and 0.11% in females. A distinct racial variation in the incidence of deficiency was observed in males: Chinese 3.94%, Malays 2.95% and Indians 0.66%. Intermediate deficiency was most frequently identified (1.83%) in Chinese females. With the preventive measures. the incidence of kernicterus has dropped dramatically and there has been, over the last 20 years, no reported cases of kernicterus in newborns with G6PD deficiency. We are now looking at issues like comparing different assay techniques and determining a shorter period of stay in hospital. We believe that all Asians, especially Chinese babies, should be screened for G6PD deficiency, irrespective of which country the child is born.

Current directions in research on autism

One of the most active areas of current research in the field of developmental disorders is autism. Since the NIH State of the Science conference, held in 1995 (Bristol et al. [1996] J. Autism Dev. Disorders 26:121-154), funding opportunities for comprehensive research programs addressing genetic, neurobiological, and behavioral aspects of this complex disorder have grown exponentially. Although we are far from having a complete understanding of the causes and deficits that define autism, significant progress has been made over the past few years. In this review, we summarize recent developments across a number of different areas of research in the field of autism, including diagnosis; defining the phenotypic features in individuals with autism; genetic bases; and neurobiological deficits.

Volatile essential oil constituents of Alpinia smithiae (Zingiberaceae)

The composition of leaf and rhizome essential oils of Alpinia smithiae that grow wild in the Western Ghats of Kerala (South India) was analysed by gas chromatography. The major components were beta-caryophyllene, sabinene, myrcene and 1,8-cineole in both samples, but variation in the yield of oil as well as the major components between the two plant parts was observed.

A comparative evaluation of coefficient of friction and mechanical properties of commercially available Foley catheters

Three commercially available urinary catheters were evaluated for their coefficient of friction and mechanical properties, which are two important parameters as far as the intended use is considered. The apparent coefficient of friction was measured from the slope of the force versus normal load graph using an in-house fabricated setup. The mechanical properties like ultimate tensile strength, elongation at break and modulus were evaluated before and after aging in synthetic urine. The swelling behavior of the catheter samples was studied in toluene and found to correlate well with the mechanical properties.