Technical Note: On modelling thermo-chemical degradation of poly(lactic acid)

A well-established model for simulation of the chain-scission process of polylacticacid (PLA) during thermal processing has been simplified and revised. The key assumption in the new model is that the total number of monomer units is invariant as reactions progress. Surprisingly, this seemingly obvious assumption appears to have been previously overlooked. The revised model no longer requires solution of simultaneous differential equations and, for isothermal conditions, an analytical solution is readily available. The present model is in excellent agreement with the more complex model and experimental results for PLA degradation reported in the literature. This simplified model has potential to be applied to other thermoplastics

Estimation of mechanical property degradation of poly(lactic acid) and flax fibre reinforced poly(lactic acid) bio-composites during thermal processing

Thermal degradation and chemical degradation are among the key issues affecting mechanical properties and ultimately utilization of natural fibre reinforced polymer (NFRP) bio-composites. In our previous work, mathematical models were used to identify thermal processing boundaries and to recognize an optimized window for NFRP bio-composites. In this study, a correlation relating the tensile strength of flax/PLA bio-composite to the processing temperature history is proposed. For the first time, an existing linear model, which corresponds to the tensile strength of natural polymers and their degree of polymerization, has been combined with reaction kinetics to predict the tensile strength of NFRP bio-composites as a function of processing temperature history. In addition, a non-linear model has been proposed which shows a significant improvement for longer periods of time, compared with the linear model. The model is based on the underlying thermo-chemical degradation processes occurring during manufacture of NFRP bio-composites. The model is capable of predicting the tensile strength of the bio-composite within 10% error

Preparation and thermal characteristics of eutectic fatty acids/Shorea javanica composite for thermal energy storage

In this study, two types of fatty acid based composite phase change material (CPCM) have been prepared by mixing-impregnation method. Myristic acid/palmitic acid/sodium palmitate (MA/PA/SP) and myristic acid/palmitic acid/sodium stearate (MA/PA/SS) were used as base eutectic PCMs and Shorea javanica (SJ) was used as a porous material to improve the thermal conductivity and thermal performance of CPCM. Thermal properties, thermal conductivity, and thermal stability of prepared CPCMs were measured using differential scanning calorimetry (DSC) thermal analysis, thermal conductivity analysis, and simultaneous thermal analyzer (STA). Furthermore, a chemical compatibility analysis has been done using Fourier transform infra-red spectrophotometer (FT-IR) and a fabricated test rig was used to determine thermal performance. It was seen that CPCMs with addition of 3 wt.% SJ presented a good improvement on thermal conductivity without any significant effect on thermal properties. No chemical reaction between initial eutectic fatty acids and SJ occurred as evidenced by FT-IR and CPCMs show a good thermal stability as well. Therefore, it is concluded that addition of Shorea javanica (SJ) into fatty acid eutectic CPCMs is appropriate to improve the thermal performance of CPCM and it can be acceptable for use as porous material for other PCMs

Using Community Health Workers to Improve Clinical Outcomes Among People Living with HIV: A Randomized Controlled Trial

AIDS-related mortality remains a leading cause of preventable death among African-Americans. We sought to determine if community health workers could improve clinical outcomes among vulnerable African-Americans living with HIV in Miami, Florida. We recruited 91 medically indigent persons with HIV viral loads ≥1,000 and/or a CD4 cell count ≤350. Patients were randomized to a community health worker (CHW) intervention or control group. Viral load and CD4 cell count data were abstracted from electronic medical records. At 12 months, the mean VL in the intervention group was log 0.9 copies/μL lower than the control group. The CD4 counts were not significantly different among the groups. Compared to the control group, patients randomized to CHWs experienced statistically significant improvements in HIV viral load. Larger multi-site studies of longer duration are needed to determine whether CHWs should be incorporated into standard treatment models for vulnerable populations living with HIV