Abstract
This study investigates the effect of post-consumer recycled (PCR) content on the application and removal torque of 28/400 continuous-thread polypropylene caps tested against 100% PCR high-density polyethylene (HDPE) detergent bottles. Three cap material variables were evaluated: virgin PP (0% PCR), 40% PCR PP, and 100% PCR PP. Torque testing was conducted using the VIBRAC 2100 Cap Inspector with an application torque set at 14 in-lb. Testing was performed in triplicate across three time intervals: 0, 30, and 60 minutes, over three runs, yielding 27 measurements per cap variable. An additional dwell-time test assessed the effect of stationary time on torque retention. Material characterization was performed using Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Fourier Transform Infrared Spectroscopy (FTIR) on all three cap variables. Results showed that 40% PCR PP caps produced the highest overall average torque at 9.51 ± 0.94 in-lb, outperforming both virgin PP (7.22 ± 1.36 in-lb) and 100% PCR PP (6.11 ± 1.06 in-lb). The dwell-time test revealed that 100% PCR PP caps experienced a 24% torque reduction compared to only 5% and 8% for virgin and 40% PCR PP caps respectively, indicating significant viscoelastic relaxation. DSC analysis confirmed PE contamination in both PCR cap variants through the presence of a secondary melting peak at approximately 128 °C, absent in virgin PP caps. TGA results showed increasing residue content with PCR level, from 0.17% in virgin PP to 1.14% in 100% PCR PP, indicating greater inorganic contamination load. FTIR confirmed PP identity across all samples with trace PE signatures in PCR caps at 720 cm⁻¹. These findings support the hypothesis that PCR content introduces material variability with measurable functional consequences for closure torque performance and seal integrity.
Publication Date
4-30-2026
Document Type
Thesis
Student Type
Graduate
Degree Name
Packaging Science(MS)
Department, Program, or Center
Packaging Science
College
College of Engineering Technology
Advisor
Chengfeng Ge
Advisor/Committee Member
Lexi Rich
Advisor/Committee Member
Christopher Donnelly
Recommended Citation
Kancharla, Sivani, "Torque Performance and Material Characterization of Post-Consumer Recycled Polypropylene Caps: A Comparative Study of Virgin, 40% PCR, and 100% PCR Closures on 100% PCR HDPE Detergent Bottles" (2026). Thesis. Rochester Institute of Technology. Accessed from
https://repository.rit.edu/theses/12614
Campus
RIT – Main Campus
