Abstract
The interactive effects between additives and weld lines, which are frequent injection-moulding defects, were studied in high-density polyethylene (HDPE) and compared to weld-line-free reference samples. These materials were formulated around a D- and I-optimal experimental design, based on a quadratic Scheffé polynomial model, with up to 60 wt% calcium carbonate, masterbatched carbon black and a stabiliser package. Where reasonable and appropriate, the behaviours of the systems were modelled using statistical techniques, for a better understanding of the underlying trends. The characterisations were performed through the use of conventional tensile testing, digital image correlation (DIC) and scanning electron microscopy (SEM). A range of complex interactive effects were found during conventional tensile testing, with DIC used to better understand and explain these effects. SEM is used to better understand the failure mechanics of some of these systems through fractography, particularly regarding particle effects. A measure is introduced to quantify the deviation of the pre-yield deformation curve from the ideal elastic case. Novel analysis of DIC results is proposed, through the use of combined time-series plots and measures quantifying the extent and localisation of peak deformation. Through this, it could be found that strong shifts in the deformation mechanisms occur as a function of formulation and the presence/absence of weld lines. Primarily, changes are noted in the onset of continuous inter- and intralamellar slip and cavitation/fibrillation, seen through the onset of localised deformation and stress-whitening.
Highlights
(“stagnation”) or at an angle (“continuous flow”) [10]. These defects have been studied across a wide range of materials, ranging from virgin polymers [10] to those highly filled with fibrous reinforcements [11,12]
The matrix was selected as an injection-moulding grade of high-density polyethylene (HDPE) (Dow HDPE 25055E, Midland, MI, USA), while the primary filler was selected as an ultra-fine, surface-coated calcium carbonate with a median particle size of 0.8 μm [45] (OMYA Hydrocarb® 95 T-OG, Oftringen, Switzerland)
The carbon black masterbatch consists of a 28% loading of a furnace black with an average particle size of 16 nm [46] (Orion Engineered Carbons Printex® F 80, Luxembourg) in a styrene-ethylene/butylene-styrene (SEBS) copolymer matrix
Summary
HDPE is among the rare commodity polymers that may be modified—through the selective addition of fillers—to be useful in engineering-type applications [1] This has become all-the-more common in recent times as a result of innovations in the compatibilisation of mineral fillers—such as calcium carbonate—that have dramatically improved the mechanical properties that may be achieved in composites containing these materials [2]. Weld lines result from the meeting of multiple melt fronts: head-on (“stagnation”) or at an angle (“continuous flow”) [10] These defects have been studied across a wide range of materials, ranging from virgin polymers [10] to those highly filled with fibrous reinforcements [11,12]. Weld lines are rarely studied in the materials described in the prior paragraph, and more rarely still across a wide range of formulations
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call