The type and concentration of additives in polymer systems play a crucial role in determining the physical, mechanical, and chemical properties of these materials, as well as influencing their processing and performance in end-use applications. However, polymer additive detection, identification, and quantification are challenging due to the very low concentrations used and the poor solubility of some additives in solvents required for testing. In addition, polymer degradation products can interact with the additives during testing. To address these challenges, various techniques have been developed. Each method offers unique advantages and challenges, including sensitivity, specificity, and limitations in the polymer systems to which it is applicable. Understanding the advantages and limitations of these methods is essential for selecting the appropriate technique for the polymer additive system under analysis. This article reviews the primary methods used for polymer additive detection, identification, and quantification, including Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, gas chromatography (GC), mass spectrometry (MS), high performance liquid chromatography (HPLC), carbon/hydrogen/nitrogen/sulfur (CHNS) analysis, inductively coupled plasma (ICP) analysis, energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). This review critically examines the challenges of qualitatively and quantitatively evaluating additive content using these methods, while highlighting their strengths and limitations, and how combinations of techniques can be used synergistically to enhance capabilities. This review aims to provide foundational insights and a potential roadmap for researchers and engineers who are beginning to explore polymer additives.

Hurricanes generate a large volume of downed timber in the southeastern United States each year. Utilizing this timber as a source of wood fibers (WFs) for reinforcing polypropylene (PP) could help mitigate landowners' economic losses. This study investigated the effects of tree age and environmental exposure on the sizes, morphologies, and surface properties of WFs from downed timber, as well as the mechanical and rheological behaviors of PP composites reinforced with these WFs at different loading levels. Tree age emerged as the dominant factor affecting strength, while loading level played a key role in enhancing stiffness, and exposure duration had a relatively minor influence. The major findings discovered that fibers with high maturity contributed to enhanced mechanical performance, while fibers from older trees, containing high extractive content, were more prone to degradation under extended exposure durations. Overall, all composite exhibited significantly higher tensile, flexural, and impact strengths than neat PP. The rheological study further explored fiber-matrix interactions, providing critical insights into the fiber quality and the processability of the composites. The WFs derived from downed timber harvested within 12 months demonstrate great potential for use as reinforcement in PP.

Understanding the correlation between morphology and the fundamental behavior of blends is crucial for tailoring their properties. This study investigated the effects of phase morphology on mechanical performance, rheology, and non-isothermal crystallization kinetics of immiscible polypropylene (PP)/high-density polyethylene (HDPE) blends. Nanometer-scale HDPE phases dispersed within PP, co-continuous phases, and micrometer-scale PP phases dispersed within HDPE were formed at 75/25, 50/50, and 25/75 PP/HDPE weight ratios, respectively. Mechanical results indicated that the co-continuous morphology dissipated energy more efficiently than the matrix-dispersed morphology. Rheological results showed that nanometer-scale dispersion significantly enhanced the blend elastic modulus through the restriction effect at the interfaces. Non-isothermal crystallization kinetics were analyzed using Jeziorny-modified Avrami, Ozawa, Mo, and Kissinger models. Due to HDPE's heterogeneous nucleation effect, the crystallization temperature of PP was elevated, and the crystallization rate of the blend also increased with higher HDPE content. Furthermore, the blend with the 25/75 PP/HDPE exhibited a higher crystallization rate than neat HDPE, as the interfacial boundaries facilitated the alignment of HDPE chains. The higher crystallization activation energy calculated in the 75/25 PP/HDPE blend suggested that nanometer-scale dispersion imposed a more significant restriction on crystal growth compared to micrometer-scale dispersion.