Sinclair, of Wild Street, Shaw, in Oldham, previously admitted one count of theft, four counts of fraud by false representation and two counts of fraud by abuse of position.
He was sentenced to three years and eight months in prison at Lincoln Crown Court on Monday.
According to the Crown Prosecution Service (CPS), Sinclair exploited his position as a packaging manager by purchasing and then selling packaging materials to recycling centres without authority from his employer, and by diverting existing stock.
He also had invoices altered to avoid detection from the company.
Det Con James Norton, from Lincolnshire Police's economic crime unit, said: "This was a calculated and sustained abuse of trust.
"Over a prolonged period, Sinclair exploited his position for personal gain, defrauding his employer of £700,904.
"This was not a momentary lapse in judgement, but a deliberate course of conduct that caused significant financial harm," he added.
"This was not a momentary lapse in judgement, but a deliberate course of conduct that caused significant financial harm," he added.
Carl Price, from the CPS, said action was being taken to recover the criminally obtained funds.